ATM and other DIY projects

telescopes, telescope-control, mounts 50cm RC austrian method of construction
50cm RC telescope-control
Stoll-control versus Autoslew(2012)
example of first generation
new projects
project of Erich Kowald 2015
project of Erich Kowald 2011
project of Erich Kowald 2009
project of H. H. Wenk 2014
project of H. H. Wenk 2010
project of H. H. Wenk 2009
first project in germany
new Windows user interface
computer-controlled focusing
automated star occultation observation
computer-controlled satellite tracking
new main-mirror ventilation
piggyback dovetail clamp at RC
piggyback dovetail clamp at C14
residual light meteor camera
repairing a old russian maksutov objective
repairing a mount of type saturn
repairing a mount of type sideres
modernization of an ancient C8
focal instruments centering equipment for refractor
T-Mount improvement
electronic DSLR-viewfinder
DSLR / C-Mount camera neck
big 60° diagonal mirror
eyepiece focussing with it
adaptation of large focuser
simple Filter Quick Changer
computer-controlled shutter
mounting of our big ccd-camera 2
residual light eyepiece
modification of a Webcam
accessories panorama head control for nexstar8i
sidereal time clock
hand control cable for nexstar
chip for Canon-Nikon adapter
handyman workshop expansion
lathe tip for thin tubes
mirror lift tool
small air dryer
big air dryer
radio clock for occultations
visor leds for C14
radiolocation for a little team member
planetary trail
a very small planetarium
observatory maintenance

new entrance to the large observatory
red light mode for PC monitor
oberver dome for 50cm RC
observer dome air conditioning
wireless sensors for climate values
wireless weather station
automated obserber dome tracking
automated observer dome positioning
minimization of heat load
remote control with two monitors
sliding roof observatory
observer dome dehumidifier
computer cabinet heating
dome-rotary drive
Flatfield light box

If you look around in the literature and also in the internet, then the amateur self-made instruments (ATM) in the last 50 years has hardly developed. There are indeed bigger telescopes built today than 50 years ago, other materials are used, other motor-types and it has been added some electronic whistles, but basically come still the same old and supposedly proven designs back. It 's so simple , if you want to make a big telescope for observer-dome: instead of small amateur equipment to enlarge, you need large professional telescopes to build smaller and always look at the references. If you follow this rule , it will be noted that the typical questions like "reflector or refractor" or "open or closed tube" and "German mount or fork mount" have answered already for a long time. As for the references, so is not only the telescope in a alleged professional observatory itself, but also the result thus achieved. Faulty designs are characterized by a lack of results. Good telescopes, however, function immediately after commissioning. Another indication is the repeated successful reconstruction of a new construction. Then there is obviously a good thing and not just bloody prototyping. So "first look, build then"

Some readers of these lines now think about heavy mounts with huge worm gears and bearing elements, elaborate drive and control technology, difficult to manufacture optical tubes made of carbon fiber composite materials (carbon has few benefits in a observatoy) ... and they will now argue that "I can not afford it private". The right solution is in the correct design. With the appropriate design, you will pass without expensive materials and components and you can build yourself much easier. Not only the usual Dobson but a genuine observatory telescope. A compact telescope of best quality with excellent tracking and positioning precision without backslash. We ourselves have demonstrated the feasibility here. We are not big earners and have no sponsors.


1996-2000: Construction of the 20" RC telescope

In 1978 the construction of entirely selfmade 40" RC telescope by Rudolf Pressberger was completed (1989 opens second operation after transfer the telescope to the Purgathofer Observatory).

Once upon a time when other telescope hobbyists grind expectantly her 6" mirrors and a 10" telescope was considered as high-end telescope for amateurs while another amateur had completely unnoticed already finished a 40" RC-mirror system. His secondary mirror was as big as the primary mirror of other advances amateurs in those days. He used a self-designed and self-built complex grinding machine in its own home workshop. Not available in USA but in good old europe. With an aperture ratio of 1:2.5 at main-mirror were from 400kg glass blank remove no less than 100kg glass (including the hole). Mirror grinders probably must not specifically explain what that means. The verification of both mirrors of the RC system was carried out with a self-developed zone measuring method without Hindlsphere and without computer assistance. The achieved accuracy of the mirror polish is a world's unsurpassed to this day. On top of this, the mirrors were done in an extremely short time. Unfortunately, he could not afford a Zerodur blank of this size.

No less spectacular is the mechanical construction of the telescope. For fork mounts entirely new principles were applied. Otherwise can be such a superior telescope with professional features not build at such low requirements on the necessary equipment in the workshop of amateurs entirely himself. After relocation of the telescope to Purgathofer Observatory the simple tracking drive was replaced by a then revolutionary Goto-control of M. Stoll.

Without exaggeration, one can say that this telescope also 35 years after its installation still stands second to none in terms of many of its properties. Amateurs who wanted to rebuild its construction were always actively supported by R. Pressberger. So already created in 1987, the first replica 16" telescope. In 1995 and 1996 drew R. Pressberger the plans for our own 20" RC (still correct on paper and not with autocad): There is a technical development with new axle bearing and friction drive. This telescope, we present here. Many replicas have since emerged after these plans.

Test setup in garage Test setup in garage

Here is to be informed primarily about the homebuilt, but also the benefits of the design are explained. A summary of the technical data you can be found under instruments . With regard to the construction plans, please see the astronomical office (Vienna, Austria), a further reference you can also be found at History. We point out that to respect the copyright of the ingenious designer Ing Rudolf Pressberger (now its descendants) use of construction is allowed only for noncommercial purposes. The same applies to the telescope-control via PC by Dr. Manfred Stoll. While we can not provide exact installation instructions here, let us describe some instructions for manufacturing and and specify the necessary tools. Numerous resulting in the construction photos are also visually convey an impression and to show that the construction really professional telescopes is not rocket science. Due to the scope of the information, we will treat the subject in the manner of a "serialized novel". The individual parts are described in *.PDF-files. To read the installation of Adobe Acrobat Reader 4.0 or higher on your computer is necessary. At the beginning I give here a list of each chapter, as I imagine it :

Benefits of the design and requirements for the construction

  • Idea and concept
    part 1 part1: general benefits of the design
  • Benefits of the design
  • The optics: compare the PDF Reader file optical errors of Cassegrain and RC with PDF Reader file theory
  • Craft skills
  • Workshop requirements

mechanical part

  • making of optical tube
    • main mirror: cell, support equipment
      optical tube
      part 2 part2: the optical tube
      78 images from construction
    • spider ring
    • secondary mirror: cell, focusing mechanism
    • carrier construction arround the declination axis
    • Serurrier rods, aperture tubes, counterweight rings
    • assembling of the optical tube
  • making the fork
  • making the equatorial base block
    • bearing elements
    • assembling
  • the drive
    • friction wheels
    • transmission
    • motor and encoder unit
  • surface treatment: prime and painting as in the garage
  • final assembly

electrical part

  • concept of the telescope control
  • control computer and interface card
  • servo amplifier
  • electrical adjustment of the drive control
  • handpaddle
  • commissioning, polar alignment and calibration of telescope model
the control
part 5 Teil5: Teleskopsteuerung nach M. Stoll
Stoll-control versus autoslew(2012)Comparison of two professional telescope controls

If you are considering the construction of a stationary telescope at home, then forget everything you have previously heard or read about homebuilt telescopes best. Not because it was all wrong but much is yet obsolete, just as some cherished idea of the construction of telescopes. The enemy of good is better and the most expensive is not necessarily the best.

Order the optics, and obtain the construction plans, tools and raw material and begin to work. You will see it is not so difficult. And if you really even need an additional tip, you're not just us, but also the other Amateurs here in europe (Austria) with homemade Pressberger telescopes (look PDF Reader filepart1 by references).

The great movie about the construction of the telescope

The famous Viennese amateur astronomer, astro cinematograph and author Herbert Csadek has turned the "official film", a 3-part Super8 film about the construction of our telescope. His film was seen already at various astronomical events in Austria and abroad

The film was re-digitized in 2008 and is now available in higher resolution and the best quality available. An informative trailer is attached. We present this silent film with a length of 70 minutes here now exclusively as 450MB-large file in Windows Media format to download. Notes are inserted in the form of subtitles. A version in DVD format can be requested. and now it starts

Pressberger-type similar fork mount of the first generation

Decades ago, Wolfgang Neszmerak from Vienna built a small fork mount (together with friends), which largely corresponds to the Pressberger design. The plans for our telescope (and its replicas in Linz, Davidschlag and others) were not yet drawn. Thus, the design follows the basic concept of large-1m RC at Purgathofer observatory. However, some drawings already show newer design features. We have looked the images and commented they, and 2013 combined in a richly illustrated PDF Reader filereport (currently only available in German language).

Wolfman's telescope

2007: new Pressberger-type telescope projects in Austria (Europe, no kangaroos)

Mr. Erich Kowald has near Markt Hartmannsdorf erected a very noble observatory itself in Styria. The private observatory private observatory Posiberg is a 2-storey building in a massive construction, well insulated and plastered white with level control room and novel cylindrical wooden dome (sheet metal Disguised and manufactured to our own design). The approximately 4m wide dome can already house a big Cassegrain. It is currently fitted temporarily with a 10 "SC telescope.

Posiberg Observatory in Styria Austria (no Kangaroos)Posiberg Observatory in Styria Austria (no Kangaroos)Posiberg Observatory in Styria Austria (no Kangaroos)Posiberg Observatory in Styria Austria (no Kangaroos)
Southwest viewNorthwest viewdome insidecontrol room

Before he went, however, to the production of his own telescope, it has already made two fork mounts for their private 40cm-Newton for club colleague of the local astronomical society Astroclub Auersbach. He has gone out of Rudolf Pressberger's plans of our 50cm-RC, has the fork arms slightly extended and adjusted the fork length to the existing truss-tube of Newton. Friction drive and bearing of tube and fork are original Pressberger type. While the first of these two mounts was still equipped with a somewhat idiosyncratic gear motor with belt drive, at second mount, the original Pressberger self-made gearbox unit was used in both axes now. The following pictures give an impression of this second telescope


16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount 16 "Newtonian with Pressberger-type fork mount
1 total view DE friction wheel 3 DE bearing 4 RA gearbox 5 RA drive 6 DE gearbox assembling

This oneself has the construction in detail further developed as follows:

  • In right ascension additional levers facilitate the adjustment between the drive shaft and the 50cm friction wheel
    (see Figure 4 and 5)
  • Both transmissions were equipped with a additional mechanical clutch which can solve the helical teeth cogwheel seated on the friction wheel-drive shaft. Connoisseur of Pressberger construction know what is talked about here. The clutch can be actuated from the outside via a screw in the concentric drilled friction-wheel drive shaft (visible in Figures 4 and 6). It allows free pivoting of the tube by hand and facilitates the balancing of the telescope. In the GoTo mode, they may not be solved, of course, otherwise the control computer is lost the position of the telescope. Maybe it manages the Styrian colleagues by manually to follow the ISS by hand, we will see.
  • The friction wheel for rektascension RA has received a wooden dust cover. (see Figure 5)
  • The friction wheel for declination DE is provided with weight-saving holes which hintan keep distortion during hardening process of steel. (see Figure 2 and 3)
  • An graceful transparent housing protects the DE friction wheel from contamination and it provides a view of the beautifully crafted wheel. (see Figure 2 and 3)

In place of the servo motor/encoder unit in conjunction with the Stoll telescope control (used for our telescope), powerful stepper motors are used in Styria (see Figure 4 and 6). They are powered by a conventional cooking FS2 type control from germany with micro-step operation.

Furthermore, Erich Kowald has developed a simple to implement method for adjusting the friction wheel drive. Together with our method (it is based on an idea by M. Stoll but not described), there are now two ways to friction-adjustment avaliable.

The experience gained during the construction, Erich Kowald now benefit for his own telescope. Certainly which is not a newton but already a real 50cm Cassegrain as it should be for a professionally built observatory. With so much exercise in telescope making Erich can manufacture its telescopic fork in record time locally in its own way, great equipped workshop. In contrast to the telescopes of his two colleagues in the club, is also the optical tube manufactured from Pressberger-type. This instrument is thus a purebred Pressberger-like telescope, in design and size comparable to the telescope of the Kepler observatory in Linz and our own telescope. Therefore, Erich has the Harpoint Observatory paid a visit in June 2007. So he could see it in full size and Natura and not just on the screen as you draw 3D animation in the CAD program. Also in the tube, Erich has some specialties. So the spider with the secondary mirror is replaceable designed to easily replace them later against a primary focus camera.

Finally, we show three views of Erich's drawing of the Pressberger-like secondary mirror unit. These are screenshots of his detailed Cad-representation, using different angles seen (copyright Erich Kowald):

 Screenshot CAD-drawing  Screenshot CAD-drawing  Screenshot CAD-drawing
a b c

The difference between Figure a and b can be seen only on the colorful arrows of the coordinate directions (approximately in the middle). This is due to the symmetry of the construction. The eye of the beholder finds two solutions for the interpretation of foreground and background. Firstly, the secondary mirror cell white below appear to stand in the foreground. The second solution of the form perception recognizes the green subscribed focus gear unit as the observer facing. Who has the images viewed by the construction of our own telescope in the gallery exactly further recognizes the bending sheets of absolutely shifting-free focusing unit, further the adjusting device for the secondary mirror and the drag arm for the limit switches of the focus gear unit (at our own telescope there is one drag arm only). The Spider plates are standing away in the drawing

Some experts came together in Harpoint. People who understood why the construction of R. Pressberger works so well and who are ready to proceed to doing. As another visitor we welcomed Mr Hannes Schmidt with us, chairman of the association Astroclub AuersBach in Styria. He has written a nice visit report on the web page of the association.

The experts at the coffee under the big lime tree The experts in Harpoint
From left to right clockwise: Howdii, Andrew, Armin, Hannes, Erich, Christian.
My chair is empty, one had to take the picture yes.

A few weeks later I was able to pay a return visit to Erich in Styria (together with Howdii). The images shown here were created there.

Mr. Hans Heinrich Wenk from Losenstein (Upper Austria) was also interested on the construction of such a mount.

We wish the new Pressberger-type telescope makers a lot of success in the practical implementation and we hope that we can further report here soon.

Thus, there will be soon in Austria more then 12 observatory-telescopes that are wholly or largely designed by Pressberger. In Germany there are already one Pressberger-type fork mount. Follow us, people!

2015: News from the telescope making by Erich Kowald

Figure 1 shows the "Master" in his great homemade Observatory-dome. Most items of the telescope were already finished at the beginning of the year, except for the paint job. Painting work can be carried out much better in the warmer months. Now the telescope is completely finished and painted, ready for final assembly. For this purpose, the base in the Observatory dome are converted from small 10 "-Meade telescope (Fig. 1) to the large 20" DIY-teleskop. Figure 7 shows, for example, the welded part of the optical-tube in an attractive white. For "factory acceptance test" the telescope was assembled again in the workshop (Figure 8 to 10). Fig. 8 shows a number of additional holes in the carrier box of the tube. Allows fan mounted (see Fig. 9), counterweights and additional optics attached, or cables are pulled through. The extra mountable secondary mirror unit with the "Spider" was not used, the connection points are shown in Fig. 9 can be seen. The blue and white color contrast is a visually quite appealing appearance (here we are not in Bavaria but in Styria). Connoisseurs of Pressberger construction know exactly what the balls are used in Fig. 4 and Fig. 5. Figure 11 shows the self-made electronics for the hand remote control.

Erich Kowald in
his dome
Fig. 2
drive Units
Fig. 3
same servomotor
as in Harpoint
Fig. 4
Bearing journal
for declination
Fig. 5
Bearing journal
for Rektaszension
Fig. 6
telescope tube
round items
Fig. 7
telescope tube
Fig. 8
test Setup
Fig. 9
test Setup
Fig. 10
test Setup
Fig. 11
Remote control
DIY electronics

Final assembly in the dome is provided after the cold season.

2014: News from the telescope making by Hans Heinrich Wenk

The finished parts of the telescope and be proud builderThe telescope in its first version as Newton is now completed. The left four images show the parts corresponding to the famous construction of Rudolf Pressberger (ÖPFM). Additional crane eyelets for mounting in the dome are necessary because the counterweight for Declination drive gearbox and friction wheel is already installed inside the fork (In our telescope in Harpoint the counterweight was only later in the fork "filled in"). Just look closely: classy can look homemade telescopes.

The three right images show parts of the Newton-tube by HH Wenk. The mirror cell is largely classical models of the ATM scene. Engineered, however, the hat of the Newton-Tube: Instead of the usual short focuser other DIY, sitting here a computer-controlled ocular sled with Linear actuator. This reminds me of the first telescope of Rudolf Pressberger 50 years ago: Its very heavy 40cm-Newton had a similar slide, but with automated hydraulic counterweight balancing. Back to telescope H.H. Wenk: fine focus or offset compensation? The secondary mirror holder is electrified.

polar wedge: In contrast to Pressberger here the outer mounting slots and crane eyelets Drive Units with gearbox (preliminary stage) after Pressberger the look in the shaving mirror
polar wedge
RA bearing
central part of optical tube gearboxes
behind RA
front DE
mirror cell
2011: News from the telescope making by Erich Kowald

The first two rows of images show you the optical tube of 50cm Cassegrain telescope after its completion in the workshop. Only the painting is still missing. The principle of counterbalance close to focal instrument flange with counterbalance-rings is good to see. The massive instrument flange can carry heavy focal-plane instruments, without tilting. You can see also the cogwheel for the focusing of the secondary mirror. A ring of small coil springs used instead of a single large coil spring, will provide the backlash of the focus. Just to test the proper weight ratios, Erich has produced a concrete dummy's instead of the mirror. They are (with aluminum foil coated) on the images visible.

telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald
optical tube
optical tube
optical tube
diagonal mirror
optical tube
instrument flange
optical tube
diagonal mirror
mirror cell instrument flange
telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald telescope making by Erich Kowald
view by
diagonal mirror
optical tube
concrete dummy
CAD-drawing tapping Erich's workshop coil spring
one of a plurality
viw by
aperture tube

In the second series of images you can see the servo motors with their coupling flange to the angle encoders. Originally a stepper motor drive was designed with the german conventionally FS2 control or the unfortunately particularly poor "Little Foot photo elegance" telescope control (which had been developed by an bad guy in Germany, which now has its customers all left alone). These controls have neither a complete proper telescope model nor a real time refraction correction. Since it is better to dispense with so many fashionable Gimmiks and even take outdated hardware purchase, but to drive his telescope with the truly professional telescope control by Dr. Manfred Stoll (just like us in Harpoint). Outstanding features of this controller are unmatched in the amateur scene even today, even in the most expensive commercially available Goto mounts ("Autoslew" is the only exception known to me). The installations required on the old DOS computers were carried out by us. 2011 we encountered in the studio of Dr. Stoll in Vienna all together. He tested his isa-bus cards for the first time along with a servo drive, the motors and the flanged angle encoders. Meanwhile, the telescope control runs together with the entire telescope on a trial basis in Styria in Erich's workshop. The parameters of the PID motor controller is based on the values used by us. With the concrete dummies in place of the telescope mirror, these parameters can be adapted to the real conditions. The parameterization of the telescope model can of course only be made after the final assembly in the observatory. The last picture shows the principle of the servo controller (simplified).

servo motor angle encoder servo motor angle encoder a bigger angle encoder (not used) clutch for encoder flange for encoder declination motor unit assembled
Servo motor
Servo motor
a bigger encoder clutch for encoder flange for encoder declination motor
unit assembled
test run with Mr. Dr. Stoll test run with Mr. Dr. Stoll Stoll-type isa bus cards Mr. Stoll and A.Kreutzer operating principle
test run with
Dr. Stoll
test run with
Dr. Stoll
isa-bus cards
Dr. M. Stoll and
Andreas Kreutzer
principle of
servo controller

2010: News from the telescope making by Hans Heinrich Wenk

The pictures show the FAT (factory acceptance test) of the mount in his own workshop and the preparation of the support box from the telescope tube. The large friction wheel for the declination axis drive is provided for weight relief with many holes. Provisionally a counterweight is mounted in place of the declination motor unit. Furthermore flange can be seen for assembling this unit. The oblique milled cylinder (clamped on the milling machine) is welded to the fork and later used to attach the declination motor unit. The large friction wheel for the hour-axis drive is just screwed to the base of the fork. Another picture from the friction wheel shows the mounting of the drive shaft on the so-called "stag beetle" (the explanation can be found in our own gallery).

Test set-up mount Test set-up mount friction wheel hour axis optical tube support box oblique milled cylinder for declination drive some parts of declination drive hour axis drive
FAT friction wheel
(hour-axis drive)
screwed on fork base
optical tube
support box
oblique milled
cylinder for
declination drive
declination drive
individual parts
hour axis drive
supporting the
drive shaft

2010: first Pressberger-type mount in Germany

As we learn only now, Mr. Michael Mross from Südergellersen near Lüneburg (northern Germany) has built a Pressberger-type mount for his 50cm Newtonian telescope. On his website you can see some pictures of the construction of the telescope. The mount is driven by high-quality stepper motors from an ordinary FS2 control from Germany. According to the builder, in Lüneburg runs everything to his complete satisfaction. The Newton with the aperture ratio of 1:4 requires a 4.5m dome and Mr. Mross is currently working just about. The dome control ideas is to be transferred from us.

Note: The telescope by Michael Mross is another successful example that the Pressberger-type fork mount is also suitable for Newtonian telescopes. The reason for the choice of Newton by Mr. Mross is to the acquisition cost of the primary mirror. I would like for more people interested in design, also seriously consider a Cassegrain optical tube (especially at an aperture of 50 cm and more). The more expensive Cassegrain mirrors are offset by lower costs for the smaller dome part again. The susceptibility to vibration is less, a visual insight much more convenient. The rising heat from body of the visual observer does not pass so easily into the optical beam path. The longer focal length of the Cassegrain is certainly not a disadvantage especially in this stable mount. The optical tube of Pressberger also has ingenious design features, such as the mount. He is far superior to many other constructions in terms of instrument load, the mirror storage, minimizing weight, the secondary mirror focusing unit and not least because of the very good collimation stability (compensation of mirror tray).

2009: News from telescope making in Styria

Erich Kowald continues to build its 50cm-Cassegrain in Styria. After the fork the optical tube is now completed in the rough construction. The entire telescope is built according to those plans that Rudolf Pressberger has drawn exactly to our own telescope mirror set. However, his optical system required a different distance between the two mirrors. Nevertheless, he was able to use the gauge (manufactured by Rudi) for our own telescope (for adjusting of mirror distance and alignement). He compensated the difference with the help of an adapter, which was produced in a single setup on the lathe.

People, may I introduce: Here is it, a original Pressberger-type optical tube.

The following images show, from left to right and from top to bottom:

  • Using of Pressberger's gauge in the production of the optical tube: The Serrurier truss were welded with the help of this gauge.
  • the front of optical tube. In the foreground you see the cogwheel of the brilliant secondary mirror focusing unit.
  • The complete optical tube with attached primary mirror cell.
  • Pressberger's gauge is attached below the focal instrument flange of the main mirror cell. The triangular plates of the rear main mirror support are inserted (Howard Grubb type).
    Two zinc bolts to hold the primary mirror lateral support elements are visible.
  • Production of 50cm friction wheels: The holes are drilled.
  • The secondary mirror cell is bolted to the Spider Ring

Bild135kB: Teleskopbau von Erich Kowald 2009

2009: New Pressberger-type fork mount under construction in Upper Austria

In Losenstein Mr. Dipl. Ing Hans-Heinrich Wenk is building a fork mount after Pressberger for his 35cm Newtonian telescope. The primary mirror of the telescope is grinded by himself. However, the mount is exactly the same as at our own telescope in order to can later upgrade to a 50cm Cassegrain. For this reason, the support box of the optical tube is already designed for this expansion. Only the mirror cells and spider ring must then be rebuilt. This proves Hans-Heinrich, that may change later to a larger optics (contrary to popular belief) even when the mount is a fork mount. Statement of the images look in tooltip (mouse set on the thumbnails).

Parts of right ascension bearing. The ball is still chrome fork in rough construction other milestones:
  • Newtonian focuser self-made and motor-driven (control via PC or by hand box)
  • friction wheels bigger then primary mirror
  • gearboxes after Pressberger
  • Stepper motors in both axes (FS2 as a control)

Sectional drawing for 35cm Newton Declination bearing pin Declination bearing
right ascension tap bearing (Pressberger-type) polar wedge: The slightly oversized oblong holes in the base are used for coarse adjustment self grounded 35cm parabolic mirror

2006: Windows user interface controlling the 50cm-RC

As a notorious DIY guy one can not only act with boilersuit in the workshop. Also on the seating area in living room with laptop on coffee table you can home-crafting your software or writing your homepage. We have already presented several times smaller software projects here (look the german version og this homepage). Now a greater chunk is added. It is about the management of our 50cm RC telescope. Until now this has always been done with the hardware and software of Dr. Manfred Stoll and runs on a 486 PC (the latter corresponds to the technical levels of the early nineties) under the old DOS operating system.

Now some readers will so ask the question why we do not use for such a large, high-quality telescope something more modern control. Since there are to buy so many beautiful GoTo telescope controllers that can be adapted to any scope. Furthermore, there are known DIY solutions, for example by Mel Bartels. Well, I have all looked on the internet and even comparisons with some high-end products made usable only with the most expensive mounts that are offered for amateur astronomers. I am still of the humble opinion that there is, at least for stationary mounted telescopes and the purse of the amateurs until today (2009) is hardly anything better than our old telescope control, fact! See also PDF Reader filehere (currently only available in German language)

This is actually not surprising, since the Stoll telescope control originally comes after all from professional use. It was developed on a process computer for the 1.5m Zeiss RC telescope at Figl Observatory on top of the Schöpfl mountain in Lower Austria (University of Vienna) and was one of the first truly well-functioning computer control systems for large telescopes in Central Europe. As you can well imagine that even the underlying standards was somewhat more exacting than what the amateur astronomer can expect today and therefore the benefits are hardly achieved before by the telescope control systems for amateur telescopes. But make sure you also have a telescope that is actually worthy for this control (of its mechanics). So much for history. For details on the telescope control by Dr. Manfred Stoll look PDF Reader filehere (currently only available in German language).

Now we found a way to break the old DOS limitations. Our telescope now controlled by a actual-type PC, which corresponds to the present state of the art. A Windows program that does not function as an alternative to the previously used control but cooperates with the Telescope Control by Dr. Stoll. All the advantages of the old telescope control remain available. On the other side suddenly open all interfaces that provides current information technology so. Without going into details, here's the screenshot of a single central operator mask of the new program. Those who have firmly decided to recreate our telescope (or already have such a telescope, controlled by hardware and software of Mr. Stoll) can get all information for free. All others should rather not look so precise, even in this one window shown here, features are already visible that are missing in most of today commercial controls of GoTo telescopes.

Screenshot of the new control software Screenshot of the new control software

The functions implemented until now are another mosaic on the way to comprehensive observatory control system, which we are specially put together for our observatory stone by stone. We take this quite deliberately no consideration for the ASCOM Initiative.

Computer controlled secondary mirror fine focusing

Focus motor with gears and limit switchesScreenshot of the old control softwareOur 50cm RC is equipped mechanically with a backlash and shifting free secondary mirror fine focusing driven by a stepper motor. This is a precise focus control without the slightest image shifting enables but the simplest construction. This mechanics comes naturally from R. Pressberger. My software has been converted from an old Atari ST computer on PC. The interface acts with a commercially available USB card (DIY kit), which has taken over the same time other control functions (tracking observer dome, fine movements). About two digital inputs on the control card, focus changing is also possible by using handpaddle. A motor step counter shows the current focus position on the screen. Every single step corresponds to less than 1 /200 mm focus change. Apart from the middle of the focus setting range, any permanently stored three focus positions are approached . After disorders (eg computer crash or power failure during the observation) provides an initialization the correspondence between true and indicated focal position restored. One extension of the software (eg for future filter wheel) and the combination with the camera control software, nothing stands in the way.

 Screenshot of the new control softwareSo an extension of the software has been made in the context of our comprehensive "observatory control system" some time ago. Although you can now save only a single focus position with the <Save> key, but this is actually so no longer required. Now we choose the particular Focal Instrument out from a list, which is mechanically rigidly connected to the instrument flange (the list can be edited as a text file). Immediately the temperature of optical tube is displayed to the current focus position where the picture in focus would be sharp (you will need manually focusing only once and then read the focus value along with the temperature and editing in this text file). If the focus motor manually operated, these temperature display changes. Conversely, we can also select or type in the currently prevailing temperature. A click on the <Fokus Nachstellen> button is enough, and we have focused the thermal expansion of the tube accordingly done. Rather than read the temperature from a thermometer and hand pretending we can also let them read cyclically from the weather station to the PC. The check box <AutoFokus> is then unlocked. With autofocus, the focus is maintained automatically at any temperature change. Conclusion: This annoying focusing in each observing night and at each change of instrument belongs now a thing of the past: Imitation people imitate!

Telescope control: automated observation of occultations
Screenshot occultationsThe calculation of occultations by the Moon, with inclusion of the topocentric coordinates is sufficiently well described in the literature. Thus, it is not difficult to write a computer program for this task. Now the reader will ask, why this is necessary. Since there are enough planetarium programs that can do this. Who also have that an interface for automating a telescope control? Obviously not. Our own tool communicates via a file interface running independently with our observatory control system. Now an automated observation of occultations is possible. In between, one can observe quiet other objects, the acoustic CountDown prevented via voice output that you missed an event. When the moon moves through a star- rich area, then observable occultations sometimes come in every few minutes. For this case, the Goto - automatic system is provided. So you get occultations sequentially presented downright from the telescope control and hear exactly when to tense look through the eyepiece. For the next ocultation of Plejades we are prepared.

On the screen shot can be seen that the calculated stellar occultations different selection criteria will apply (horizon height, magnitude and type of coverage).

  • Wolfgang Wepner Mathematisches Hilfsbuch für Studierende und Freunde der Astronomie
  • Oliver Montenbruck Grundlagen der Ephemeridenrechnung
  • O. Montenbruck, T.Pfleger Astronomie mit dem Personal Computer

2007-2008: Satellite tracking by computer controlled motion
By an extension of our observatory control system, we can now track satellites with known orbital elements (TLE) in the large telescope. Using computer controlled motion in both axes with variable speed during satellite overflight. The deviations between the actual orbit and the predicted path are being compensated by manually guiding. In contrast to other colleagues with similar projects we are currently (2008) working without any finder scope. The visual tracking corrections are made by the DSLR camera viewfinder wich the images are recorded. Thus, the observation of the international space station ISS is even possible during the day.

Screenshot orbiting satellitesScreenshot geostationary satellites

Details on the applied methods and the interface between the host and the telescope control, we will publish later. However, we have written two technical articles, which describe the basic methods for observing satellites with telescopes (currently only available in German language). From the results obtained, the reader can check by viewing our gallery.

Active primary mirror ventilation in our large telescope
The housing to accommodate the fans are cut from aluminum sheet 1.5mm and bent into shape in a vice. Form and function form a unit with the aesthetics of the telescope Fine dust filter flow embeds the fans. This also a decoupling of motor vibration is produced Here, the air flow this cross flow fan is indicated. The narrow air outlet opening has been adapted to the gap between the mirror cell and tube supply box with a flow baffle Here you can see the narrow gap between the mirror cell and supply box. The air is directed directly to the surface of the main mirror Installation is very simple one of four fans The connection cable between the fans are passed through the seal tube between support box and mirror cell Test set-up in their own small electronics lab Simple design of the speed control. At the observatory control system computers off can be switched to manual operation The interface, the speed control for our observatory control system software is produced by the PWM output of the USB control card K8055 Fan for the main mirror cell: circuit diagram of speed control: With widely available standard components instead of a microcontroller that anyone can replicate. Only the BU508 holds up to 1800V and is thus admittedly oversized. The was just the way around Cabling in the tube Test in practice: The time course of cooling of the primary mirror by turning on the fan has been documented with our wireless weather station Screenshot of the fan control in manual mode

A part of our project "dome air conditioning" refers to the active ventilation of the primary. Our main mirror with a weight of 40kg pure Astro-Sital has a high heat capacity. This circumstance delays the temperature compensation of the mirror with the ambient temperature at rapid changes in the evening or morning. Although there is no relevant deformation of the mirror surface (as opposed to Pyrex or Duran), laminar air streaks can ascend along the mirror surface in the optical path of the telescope. Although this air streaks escape with our open tube, they still deteriorate the seeing of the telescope. To avoid this we need cooling the dome on hot days in the early afternoon. Similar problems arise with rapid temperature drop at night during the observation. The main mirror temperature can not follow fast enough. The temperature difference between the mirror and the surrounding area has increased again during the night.

If we want to observe with the large telescope after sunrise in the morning (for example, the ISS during their overflight), commonly occurs on the reverse case. Too cold mirror relative to the ambient temperature may cloud over when the dew point is reached.

In both cases, the active mirror ventilation can help. In contrast to most other telescopes (with active ventilation), our fans are not behind the primary mirror. 4 strong cross-flow fans (Papst) blown cleaned air by 1cm wide lateral slots between the mirror cell and the support box of optical tube on the front of the primary mirror, directly radially beyond the optical mirror surface. The fan is elastically mounted to the support box of optical tube and operated with 24V 0.6A each. No vibration is visible in the eyepiece, even at high speed. Fan Speed ​​is set via our self-developed observatory control system, depending on the telemetered data from wireless weather station sensors (mirror temperature, dome indoor temperature and outdoor temperature). Alternatively, switched to manual control, and the fan can be adjusted by a simple potentiometer, operated without computer.

with the application of the mirror ventilation and ventilating in the dome two intersections in the temperature curve are significantly:

  • Outside temperature is below the temperature inside the dome
  • Internal temperature of the dome chamber falls below the temperature of the main mirror

As soon as the outside temperature has dropped in the late afternoon with the temperature inside the dome, the door of the observation gap and the front door to the observatory opens. Normally, two to three hours later is the case prior to start of observation. The dome (a rotatable roof with a square cross-section) is placed in 45 degrees position against the square base. This results in 4 large additional openings to the outside to support the exchange of air.

A strong fan blows the now cooler outside air into the interior of the room.

Now the temperatures from inside the dome and from the main mirror are to be compared. If the interior temperature of the room is less as those of the main mirror, the fan for circulating air in the cabin is directed to the rear side of the mirror cell. There, the four cross-flow fan, the mirror ventilation have their intake. The primary mirror ventilation is set in motion at high fan speed (manually or computer-controlled). Are the temperatures approximately equal, the fan speed can be reduced

Application of the mirror ventilation together with the dome air conditioning:

This procedure is then used when either there is no prospect that on a hot summer day, a temperature compensation between the telescope and the outside air can be done by ventilating alone, or if an early start of observation is still required in the twilight, and therefore the time for airing runs short . Then, in hermetically closed dome we use our air conditioning. under the evaporator of the air conditioning (it is located on the wall) is created cooled air to the floor. From there you will be captured by our great fan and blown up to the main mirror cell of the telescope. The four cross-flow fans carry the cold air directly to the mirror surface

Active ventilation during the observation:

If a temperature difference of more than 1 to 2 degrees Celsius remains between the primary mirror and environment, then the fans are also used during the observation. This is possible because the vibrations of the fan in our sturdy tube shows no adverse effects. The air flow in front of the mirror swirled so the resulting air streaks and blows it with a turbulent flow from the tube. Turbulent air flows in the optical path of the telescope does not interfere with the seeing, if the moving air practically has the same temperature as the environment. In this way, the strong temperature gradient in the observation night is acceptable.

More pictures of the construction can be found here

piggyback dovetail clamp at RC
 Preparation of the surfaces with the 60-degree dovetail cutter Production of the 60-degree sliding surfaces on the milling machine of our telescope making workshop30. The rails after production on the milling machine the functioning is visible here. All surfaces are milled. Anodizing is still missing. the functioning is visible here. All surfaces are milled. Anodizing is still missing. the functioning is visible here. All surfaces are milled. Anodizing is still missing. 4 stainless M5 screws holding the rail rock solid on the telescope tube The small refractor can be mounted on the northwest corner or in this case at the northeast corner. The counterweights are accurate to mount opposite the refractor The counterweights stainless steel consist of modules with 1kg or 2kg. They are eccentric bolted to the prism shoe. In order for a By pivoting is possible through the telescopic fork. Thus, it looks after assembly. Discreet and unobtrusive

The optical tube of our 50cm-RC offers along the four beveled edges of the support box a view to the sky. Because the support box has a material thickness of 4mm, also weighty additional optical instruments can be attached there. For all four edges, therefore, a suitable 4cm wide and 25cm long dovetail plate rail was manufactured and attached with stainless M5 screws. Due to the high manufacturing accuracy of the supporting box all 4 rails are largely parallel. The two south-facing rails are provided for attaching counterweights. These are eccentric to the beveled edges of the support box arranged so that a pivot past the telescopic fork is possible. The additional counterweights of collapsible modules with one to two pounds of weight made of stainless steel. The two north-facing prism rails can then carry the additional optical instruments. We are thinking of cameras with telephoto lenses, small refractors, electronic viewfinder for monitoring of the visual field or laser for small lidar experiments. Because of the equatorial mount, the additional instruments do not affect to the two arms of the fork. The choice of two different mounting points makes it possible to optimize the viewing height of the additional instruments and the orientation of the observation slit of the dome, depending on the observation hemisphere (east or west) . The automated dome-control (described PDF Reader filehere currently only available in German language) is adjustable for additional instruments. Our old 4 "refractor (TeleVue Genesis) was tested as an additional instrument first. He could help in finding the International Space Station near the horizon, if their orbital elements have again such a large mistake that ISS despite precise positioning of the telescope to the predicted start point satellite tracking, does not appear in the visual field of the RC. For the actual tracking of satellites normally we need no viewfinder. The main application of the additional refractor is the comparison of set objects at different magnification and visual observation. During guided tours, our visitors get to this way a better feel for the dimensions of the celestial objects shown and the performance of the big telescope. Fact that the refractor has the same painting as the large telescope is pure coincidence. But the picture also shows that one can easily get a head beating. Together with an attached digital SLR camera and the counterweights on the opposite edge of the telescope, the more load on the fork mount is about 12Kg. However, this does not impair the already high positioning and tracking accuracy, although we have made no adjustment of the telescope model in the telescope control (also because you recognize a properly constructed telescope ). In our gallery is furthermore the production of the parts seen in our telescope making workshop .

piggyback dovetail clamp at C14

Similar to the rail system described above for additional optics at the 50cm telescope, we have now created such a of mounting to the C14. We wanted it to use commercially available components and have experienced such a nasty surprise. Here is our test report on the application of "Starway dovetail clamps Vixen GP Level"

the repaired dovetail clamp mounted between the telescope tube rings

Construction of low-light meteor camera

the whole meteor camera The heart of meteor camera is a 3-stage image intensifier of the first generation. Its 18mm photocathode needs to be protected from strong light. We have built a slider, similar to the film magazine slide of old medium format cameras. The slider is opened only in the dark. Before the slide sits a mounting flange which makes it possible to use different lenses from Nikon F mount to the System-64-telescope approach. On the other side of the residual light tube, the image of green fluorescent screen must now be mapped using a relay optics onto the CCD black-and-white video camera or webcam. Unfortunately, is lost in a lot of light. The opening ratio of the relay optics should be as large as possible. We use the lens of a super8 film camera with 10mm focal length and an aperture ratio of 1:1. The professional (and correspondingly expensive) option would be a fiber-optic coupling. But this is a demand for a specially adapted CCD.

our camera with fisheye optics With an 8mm fisheye lens we have used the meteor camera as an all-sky camera. The meteor camera is mounted on a wooden tripod and placed in an open area. To protect against dew the camera is surrounded by a cylinder of thin acrylic glass. A small heater is allowed to flow from the bottom heated air through these cylinders. With seeing by rising heated air is no concern for the fish-eye lens. If the moon shine on the direct moon light from the residual light tube must be kept away. This is done by a semi-circular shade bow, which is aligned with the moon's orbit. For the transmission of the video signal standard video transmitters are very good at 2.4MHz or 5.8MHz. With a satellite dish, we transmit the video signal to the VCR in the living room. The high voltage generator of the residual light tube is operated with 12V DC voltage. Also, the video camera, the video transmitter and the heater. The whole assembly can therefore be independent of the mains also set up in a field.

Unfortunately, our residual light tube has considerable sensitivity lost with time. So now we no longer use them.

Repairing a old russian maksutov objective
The design-related, more or less on most devices existing strain of the optics is reliably eliminated. Further improvements to facilitate the application. The changes are described PDF Reader file here (currently only available in German language)

Repairing a mount of type Saturn

With a little technical skill and experience with telescope drives you will make from an old "Vixen Saturn" a precision mount that can hold not only in stability but also in terms of tracking accuracy with the mounts available today. The changes are described PDF Reader file here (currently only available in German language).

Repairing a mount of type Sideres

Sideres is the name of a big German type mount that is made in Germany. The reason for the renovation was an acute incident: The tracking did not go because the drive was rusted. The original state of the mount was restored by the refurbishment activities. It came to light hidden design and construction defects. These deficiencies have also been eliminated. The planned expansion of the mount on Goto-operation has not yet been tackled. The changes are described PDF Reader file here (currently only available in German language).

Modernization of an ancient C8

On our observatory all started in the 80s. With a classic C8 telescope in orange-gray finish. The 30-year-old telescope has now been brought down from the attic and equipped with a newer mount. This mount is a "one-armed bandits", which goes by the name "Nexstar8i". A PDF Reader filereport (currently only available in German language) provides further information about the required adaptations, a comprehensive practice test and shows alternative application possibilities. A self-written program for remote operation, see PDF Reader filehere.

Single arm fork mounts are not suitable for large telescopes, although some manufacturers offer that. However, until the size of a C8 telescope it is acceptable.

Focal instruments

Electronic Viewfinder for DSLR Cameras

Old DSLR cameras have no live video display on the rear LCD screen just as you would expect from small digital cameras. The current generation of DSLR cameras, alternatively to the optical viewfinder come up with a live image display. This does not mean at all that one can also see so deep-sky objects with the camera on the telescope. We have developed a removable electronic viewfinder for DSLR cameras, which can. He works with an external monitor, it saves so the neck sprains and protects his intervertebral discs. On top of that our viewfinder can be easily reconstructed. A detailed description can be found PDF Reader filehere (currently only available in German language).

DSLR / C-Mount camera neck

watec videocam at focus planewatec videocam at focus planecamera neck partscamera neck with shapley lenscamera neck on the latheimaging source DBK at focus plane

While our professional CCD camera 2 already had a rigid connection at the big telescope, we had the smaller cameras attach to the focuser (as do most amateurs). This has now come to an end. For the DSLR Canon EOS5D2 and for small CCD cameras with C / CS-Mount, we now also have a rigid connection to our telescope made. The mounting flange to the telescope is made of aluminum and has a diameter of 24cm and a wall thickness of 2cm. Because a solid aluminum tube is screwed with a 9cm diameter and 5mm wall thickness. The tube could also take a focal reducer or a field flattener. At the end of the pipe different adapters are possible: On the one hand, an intermediate piece with T2 ring and Canon EOS lens mount, on the other hand, an intermediate piece with manual filter slider (he was here already described) with 42mm lens thread to which the C / CS mount adapter is recognized. The images show the aluminum components before the anodizing with black anodised color (our anodising station we will take only operates in winter). The optical length of the tube and the spacers are dimensioned such that at a temperature of 5 ° C and the center position of our motorized secondary mirror focusing the focus position of cameras is achieved. With selection of the focal instrument in the software of the observatory control system remaining inaccuracies in the production are compensated. The focus motor adjusts the focus correctly. This self-written software does the temperature compensation of focus, so that the focuser usual annoying focusing omitted...

Big 60° diagonal mirror

parts of the zenital mirror housing inside parts of the zenital mirror black anodised the diagonal mirror To improve the insight on the telescope position and thus avoid dislocations of the cervical vertebrae of the observer, we needed a 60-degree deflection. But we wanted to use 2 "eyepieces without vignetting. Commercially since nothing is appropriate available only DIY remains. As a visual element, we use a large plane mirror, as it is usually used as secondary mirrors for Newtonian telescopes. He has an accuracy of Lamda/10. The housing we have made of an aluminum-shaped tube with 10cm edge length and aluminum plate material with 5mm wall thickness. Telescope side, the diagonal has a system-64 connector on the eyepiece side a 2 "plug sleeve. The different size on both sides prevents vignetting in our 1:8 beam path

eyepiece focusing on the 60° zenith mirror

helical focuser short distanceFor visual use of our 50cm RC telescope, the system 64 focuser trademark Lichtenknecker we flanges along with our 60° diagonal mirror. Although the focuser has a large adjustment path of 12cm, but he is hard to use for visitors. The fine adjustment we make electrically with our secondary mirror focusing. The focus can be adjusted so that, although very accurate, but only by about 1cm. The combined use of mechanical rough adjustment and electrical fine adjustment has proved too cumbersome in practice for visitors. So we held out for ways to improve upon visual experience.

helical focuser long distanceIn the ATM scene has already been several attempts to use-the adjustment mechanism of photographic lenses for focusing of eyepieces. The fact that the front lens of the lenses or after the conversion the eyepieces rotate during focusing, does not matter (apart from ocular reticle) in contrast to the photographic experience. With "cored" miniature lens versions you can only focusing one and a quarter-inch eyepieces. Nowadays, you can also buy ready small helical focuser.For 2 "eyepieces, the diameter of small format lenses is not sufficient and the adjustment path is usually too low. You have as approaching already on the mechanics of medium format macro lenses. The tube of the" Russians ton "and similarly structured optics would be also suitable in principle, is but again too big (and who sacrifices his already like Russians ton). We have implemented a different solution. In Scavenge crate from a photo flea market, we found parts of the "Leica Focoslide". There is a camera sled with ground glass and arming screw, a former accessory for macro photography with the Leica-M. Because of his straight right diameter and an adjustment path of almost 3cm, this helical focusing mount is threaded with multi-course movement from watchmakers brass, quite excellent for focusing of heavy two-inch eyepieces.helical fokuser + eyepiece + mirror After some fine mechanical adaptation work in our workshop the focusing mount with the inscription "Leitz Wetzlar" now replaces the simple 2 "eyepiece clamp clip of our large 60 ° zenith mirror. This allows the common question asked by visitors to our observatory "where one focuses here?" yet easier to answer: turn the eyepiece

Adapt an old focuser of the manufacturer Lichtenknecker

bevel gear drive clamping disc The old big System64 focuser of Lichtenknecker has 12cm extension length and fits with its 85mm outer diameter loose in the aperture tube of our 50cm telescope. The hand wheel and the clamping screw is in this case lowered into the bore of the main mirror. To get at this adjustment, we used a small bevel gear drive. The bevel gear made of model components is housed in the aperture tube. Despite its size and the massive construction of the focuser is only suitable for visual use, since it does not work free of tilt and is clamped at only one point. We also need it only for coarse focusing, since we have to fine-tune our completely without tilting the secondary mirror focusing.

simple filter quick changer

Filter slide for 3 filter sizes Inserted filter drawer A simple, manual filter drawer is made of aluminum and brass. It is equipped on both sides with T2 thread. He takes on filter with 1.25 "and 2" eyepiece thread, but also filter with the Nikon 52mm filter thread. There are 3 different filter slide, which can capture a single filter, respectively. With the help of the slide they are placed in the beam path. Sealing lips made ​​of black silicone provide sufficient light leaks.

Electronically controlled mechanical shutter for CCD camera of the German manufacturer OES

the camera with shutter and filter drawer front of shutter shutter with DIY electronics The mechanical shutter with 2cm diameter comes from a dismantled video lens. He was there used as a two-blade shutter to aperture control. Tests have shown that a minimum exposure time of approximately 20 msec is achievable by controlling voltage pulses. Normally, the unit is controlled with its own computer-plug. Thus, the manufacturer of the camera OES LcCCD-11 it has provided. We do not use the computer plug and use our own electronics for the pulse treatment. It is mounted on the camera and controlled via the 50-pin connector. The supply voltage for our home electronics is derived from the camera connector (right angle plug in the picture). During the exposure, the red LED lights. An additional TTL output allows the further rotation of the filter wheel (socket with green LED). The switch at the top left disables the shutter for making dark pictures. On the top right, you can also connect a classic cable release, but this is just a small gimmick of the developer. To the left of the fan is actually a bicycle valve visible. So that we can fill the camera inside with dry nitrogen. We use a leftover gas bottle from my old photo lab from hyper sensitize of chemical films. My DIY electronics worked well, it is a pity that the whole camera is now outdated.

mounting of our CCD camera number 2

the additional housing with new flange (left), the original flange (right) milling the flange the new flange before anodising Our large CCD camera of the American manufacturer Roper Scientific (formerly Princeton Instruments) comes standard with a 35mm shutter and Nikon bayonet. We call them our second camera. The heavy camera (4kg) so to hang from the telescope is not very convenient. We therefore replace the front panel of the camera by a milled aluminum flange of 16cm diameter, which also accommodates the new 45mm wide-shutter (Uniblitz) by Vincent Associates.

In the first "field trials" it has come to a freezing of the camera optical window already at moderate cooling (-10° C). To remedy this situation was constructed an electrically operated air dryer, which constantly circulates the air in front of the camera window. The corresponding air channels provided with a light trap embedded in the camera flange. Now no problem cooling is possible below -20° C. Usually we cool the CCD to a temperature of -40° C, even in summer. The lowest temperature that we obtained with good high vacuum in front of the CCD, is -55° C.

the complete cooling and drying mechanism the complete cooling and drying mechanism The camera also get a protective casing for holding our additional water cooling. We thus replace the existing secondary optional water cooling. Thereby, the dew condensation is prevented at the internal condenser, and thus preventing possible moisture on the camera electronics and the cooling water temperature can be lowered to values of below 0° C. The cooling water hoses are thermally insulated for the purpose. In the orginal manufacturer available optional liquid cooling, the cooling water temperature is limited because of the dew. If the camera is used outside the dome without liquid cooling outdoors, the additional housing can be opened and the built-in camera fan provides for heat removal from the 3-stage Peltier element (about 90W max). The heat transfer to the surroundings plays here (in contrast to the dome room) does not matter.

camera equipped for outdoor use with tele lens and little air dryer Alternatively, for connection to our large telescope, a lensboard with NIKON mount and rear lens Filter sliders can be attached to the new camera flange. It can be used the same Filter sliders, which are also in the filter drawer for use.
Our experience with the operation of the camera we were able to assist an astronomical institute in taiwan. At this university Lulin Observatory, there were the same problems with the too small shutter and with dew on the camera window. This camera is used there on a twice as large telescope.

Residual light amplifier eyepiece

the screen enlargement residual light amplifier eyepiece with power supply The residual light amplifier eyepiece consists of the 3-stage image intensifier which is also used on the meteor camera. Cathode side, it is equipped with a 2"eyepiece holder and a magazine slider to protect the sensitive photocathode. A projection lens of a video projector serves as oversized viewfinder magnifier and enlarges the small fluorescent screen of the image intensifier to seemingly 10cm diameter. Disturbing is the length and weight of the arrangement and flickering of the secondary electrons. What characteristics of an image intensifier gen1 are useful for astronomy? The H-alpha spectral line (for the eye not visible) can be transformed with the appropriate photo-cathode in a green light. It works like this: The emitted electron from the cathode are accelerated with high voltage and stimulate the phosphor screen of the anode at a green light. The electron optics provides the pictorial representation on the screen. In our 3-stage tube, this is done three times in a row. The advantage over CCD is the real-time behavior. You do not have to wait for an exposure time. You see the object immediately on the luminescent screen. In the practice can be mentioned the following advantages:

  • Gaseous nebulae are in H-alpha light visible visually (especially with H-alpha filter)
  • because of that the horse head nebulae is bright and clearly visible to everyone in full moonlight
  • In brighter galaxies dark clouds and spiral arms are much more evident
  • In large galaxies like M33, the star-forming regions are actually visually apparent
  • no dark adaptation required
  • Several observers can simultaneously look at the fluorescent screen from 50cm distance
Unfortunately there is a serious disadvantage: Because it is an image intensifier of type gen1, the sensitivity has in course of time greatly diminished. The photocathode gradually loses its ability to emit electrons and thus the sensitivity to light.That's a pity. Today, recognized for these applications a EMCCD (Electron multiplying charge-coupled device). In contrast to the old gen1 tubes EMCCD are too expensive for amateurs like us. The americans are also very strict on the sale of militarily usable items. Now we could take European products here in Europe, but our politicians are the americans very obedient. Since the affair NSA did not change this.

Modification of a Webcam

mounting the CCD board 2 concentric threads Also, we used for a long time a widely used webcam among amateur circles, the TOU-CAM PRO Phillips. However, the egg-shaped housing is not very practical. We have the camera board therefore packed in a more solid housing which is provided with both a tripod thread and with an additional C-mount lens mount. The original lens of Phillips 12mm thread can also be used. Therefore, the following combinations are possible:

  • 1-1/4 "eyepiece holder with IR cut filter for use at the telescope
  • C / CS-mount video lenses or lenses from 8mm film cameras
  • NIKON camera lenses via adapter C-Mount/Nikon
  • Original lens and other small video lenses with 12mm thread
  • Eyepiece projection with original lens and 1-1/4 "eyepiece tubes
  • Digital camera accessories lenses for NIKON Coolpix cameras-along with original optics (Fish-eye and extreme wide angle with high optical quality)

The images show the mounting of the camera board in the new housing and the two concentric lens thread. Applications are described in instruments. An additional Peltier cooling of the entire electronic system is easy to implement with the new housing. Tests with a cold spray , however, have found only a modest effect of cooling. From the widespread restructuring of the electronics for longer exposure times, we have also taken the distance. At best, you can then use the thing yet as a Guider, but for deep sky shots there are much better cameras, also you can build yourself. The enthusiasm in some Internet forums for a noisy image of M57 with one hour exposure time (taken with a converted webcam) is not comprehensible way for us. And if you so much solder (Turn off the read-out amplifier at the exposure, direct cooling of the CCD, 12-bit ADC, etc.) from the "ugly little egg" will never slip a "proud swan" .

Refractor centering device

Our refractor centering device can be very easily prepared from yourself in a small workshop. You only need 3 LED on a ring in an eyepiece plug sleeve. It uses the reflections on the lens surfaces of LEDs arranged concentrically to the optical axis: The test optics is then centered when you watch form from the optical axis reflexes a concentric pattern. If this is too vague, you can supplement with an alignment telescope arrangement. The whole thing is described in detail PDF Reader filehere (currently only available in German language). To center our great RC telescope, however, more is needed.

T2-Mount improvement

For the small and light DSLR cameras, it is perhaps not so noticed. In the heavy cameras with full-frame chip, it comes already more frequently: We talk about tilting of the camera on the lens bayonet. How you can take action against it, we show PDF Reader filehere (currently only available in German language).


Pan head control for Nexstar mount

For our "armed bandit" Celestron Nexstar8i we have developed a control program for remote operation some time ago. Parts of our observatory control system were adopted here, so that its elegant operation partially shows up here again. We have not been presented in this page, there already exist many similar programs for controlling the Nexstar mount via PC and partially also available as a freeware. They are all based on the published Celestron transmission protocol to the serial port of the mount. We have used the remote operation so far only for visual use of the telescope (visitor mode at the starry night tours).

Our PDF Reader filesoftware has now been complemented by a panoramic head control. Other Nexstar-operation programs do not have this. Despite the azimuthal-up the Nexstar Mount is now also available for photographic starry horizon panoramas (with azimuthal tracking). With parallactic sub-base spherical panos from the starry sky are possible (programmed but not yet tested). These two functions are not available on commercially Pano heads for normal photography. Additionally, implements all conventional Pano head for panoramic photography functions (see example picture) as they also available at other motorized pano heads.

Since the software (as mentioned) is not yet fully tested, it is not generally available for download.

sidereal clock

After the PDF Reader filerenovation of the Sideres-85 mount, we need a sidereal clock again to use the pitch circle of the hour axis. A short PDF Reader filereport describes our software clock for this purpose quickly programmed, as well as those hardware clock that I built over 30 years ago. The software clock can be downloaded as freeware. All this is currently only available in German language.

a chip for Canon Nikon adapter

A well-known advantage of the Canon EOS lens mount is the large diameter and the smaller Backfocus compared with other manufacturers of DSLR cameras, like Nikon, Olympus, Leica R, Pentax, M42 etc. Among Backfocus I mean the distance between the contact surface of the lens mount on the camera and the film plane today the sensor surface (also called flange focal distance). This advantage allows the use of adapters for connection of external lenses with different lens mounts. If the adapter just as "thick" is like the difference in the back focus (fairly accurate 2.5mm for Nikon), then let the foreign lenses also on the Canon to the distance "infinity" focus, the distance scale is thus obtained without an additional lens in the need to adapater.

The Novoflex company provides such an adapter, albeit at a handsome price. Significantly less expensive adapters are made in China. They are mechanically quite solidly constructed, but have a thickness of only 2.15mm. When using this adapter the distance scale of the lens moves a little and you can all lenses attached easily turn the setting "infinite" beyond. In some cases, this can even be advantageous. The length change due to temperature makes it necessary for tele lenses.

Of course you can not expect miracles with the use of lenses with foreign bayonets. On a mechanical iris diaphragm function (and thus to a metering at full aperture) you will have to do without just like an auto focus. But at least with working aperture exposure metering is possible without restriction in Canon. Not so with the entry level DSLR from Nikon.Unlike Nikon, you can only use Canon electronic focusing aid of the camera when the electronics of the objective lens reports the data to the camera. You know those focusing aid of Canon EF lenses when switching to manual focus. The focus sensor of the EOS 5D and EOS5DMk2 works even without AF assist light very well (in bright ambient light even to the aperture 8). Without electrical contact with the lens, it does not work.

the adapter is ready for use Nowadays, there are ready to buy adapter with these electronics. We had the adapter itself still combine with the electronics. We have milled a small groove in the lens adapter.

the 2 parts before assemblingmilling the pin awayHowever, a disadvantage of this solution is not to be concealed. The self-fortified electronics board is slightly wider at one end and can collide with a pin in some Nikon lenses (AI-S cams) protruding into the camera body. This pin has a function with only a few camera models (Nikon FA, 301, 501). It has nothing to do with the automatic diaphragm function. Newer Nikon lenses have the AI-S pin only for backward compatibility. The pin can therefore be removed without detriment to the usefulness of the lens to Nikon housings. Be it reversible by unscrew the rear dust shield directly to the mount of the lens or definitely file off by, saw off ground away etc. You should anyway always carefully check whether the recognized age-old lenses not to far into the mirror box of the Canon camera and thus may interfere with the mirror movement.the adapter is ready for use

Practical experience
The electronic focusing aid is an adequate substitute for the missing microprism or split image focusing screen of the camera viewfinder at normal photo opportunities. Such tools do you know of the chemical Photography of earlier times. In this way we were able to successfully use high quality Nikon telephoto lenses and macro lenses to the EOS5D and EOS5DMk2. For the focus on the astronomical application at the night sky denied even the electronic focusing aid of the camera. With "Live View" you can to focus on bright stars quite well. Another possibility into focus with electronic support even when using the camera in the focus of the telescope, is our self-built electronic viewfinder for EOS5D, which in contrast to "Live View" is also suitable for faint celestial objects. The knife-edge method is still unsurpassed For the very accurate focus of stars. We have tested the commercially available focusing aid "Shure Sharp", which works according to this method. A Review for the camera EOS5D yourself, see here (currently only available in German language).

handyman workshop expansion

The tools required for the construction of the great telescope have already been listed in the specifications - PDF Reader filesection1. This is about the question of how to get inexpensive device for their own workshop and many necessary tools itself can customize for the operation of machine tools. The extensively illustrated - PDF Reader fileReport is a treasure trove for ATM interested especially with ambitions towards metal processing. He is one of the most read on our page (currently only available in German language).

mirror lift tool

mirror lifter Our main mirror with a weight of about 40 kg (88 pounds) can be taken safely with the help of the mirror lifter on the 15cm mirror bore and raised. This makes possible the convenient removal and installation of the mirror in the mirror cell (necessary eg for mirror cleaning with other telescopes). The hole for hanging crane hooks our DIY dome crane or a handle may be attached.

the little air dryer

inside the little air dryer the little air dryer Our air dryer is operated with two Peltier elements, which emit heat over a copper cooler on a liquid cooling. It can be attached to the cooling circuit of our CCD camera number 2. A small CPU fan provides air circulation on cold side of the peltier elements. Dry cool air is supplied through a 10mm silicone hose to the drying device. With a second hose to the intake port and air recirculation mode is possible. The device is intended for portable use of the CCD camera number 2 outside the observatory and can also be operated with a lead acid battery.

Basic considerations for drying of CCD windows are described PDF Reader filehere (currently only available in German language).

the big air dryer

adapted freezer box air pump and air fine filter Useful only for stationary use in observatories a system which consists of a freezer box with appropriate hose connections is (recessed into the door), an air pump (for inflatable boats) and an air fine filter (expanded from an old removable disk drive). Thus large amounts of dry and dust-free air can be produced. Except for focal-plane instruments, the system is also suitable for dry keeping of telescope optics and avoid Mirrorseeing.

Radio clock for measuring Occultations of Stars

We want to provide videos with exact time marks. These time stamps can be made subsequently an exact temporal allocation of occultation events. In principle, it is sufficient to show a clock in the video, and then to document the occultation event on video without interrupting the recording process. About the fixed number of frames per second, the time allocation is determined by count of frames between clock and event. Previously you looking to the eyepiece of your telescope, had to use a stopwatch and consider the human reaction time with a personal equation.

But which clock you shall show in your video? Since there is a wide range of possibilities. Grandma's kitchen clock is definitely too vague and my private atomic clock I foolishly just not in the house. Joking aside, this would also be exaggerated. We need for occultations really only achieve a precision up to 1/10 sec. Due'll additionally interpolate between the individual images from the video. Our range is between radio-controlled clocks and watches with exact GPS time and video time inserter. Latter would be ten times more precise than necessary, but are expensive. The time from the Internet is usually not as accurate: The time from an NTP time server would be accurate enough (because runtimes signal included), but on a home PC is commonly found only the simpler SNTP and you can compare more with the kitchen clock from grandmother, honestly. Do not believe that your smart phone has a more accurate time, although there is a GPS receiver installed.

Back to our solution. We use a radio controlled clock with LCD display. There are, unfortunately a little problem. The LCD displays react very slowly at night when cold, radio controlled clock with LED indicators are hard to find and radio controlled watches with conventional mechanical clock hands are rather large and unwieldy, and the pointers may be twisted.

The solution is to display the time signal transmitter pulses by an LED that flashes every second and is recorded with the digital display of the clock. The "rough time" you see in the LCD display and the "fine time" with the LED. Since the clock is seen in the video several seconds, a subsequent compensation calculation and interpolation is possible.

our occultation clock Here in Europe, we use the time signal transmitter DCF77 in Germany. You have to look at the clock module, only the output of the receiver. Then the LED is controlled by a transistor. The receiver is only activated once per hour in many radio-controlled clocks to save power. You must seek this circuit and then disconnect the conductor. Thus, the receiver is always active. You can also make him be activated with an external switch. The LED is also used to receive control. She shows you receiving disorders at by irregular flashing. So you can better align the clock to the transmitter.

The visible connector in our picture allows the synchronization of a computer. In addition, even the DCF77 telegram pulse is available there. The switch turns the receiver on. The button resets the clock. A piezo buzzer creaks to the rhythm of the DCF77 telegram (second).

supplement 2009:

In ordinary radio controlled watches the DCF77 receiver are built for narrow-band receiving. Although this increases the insensitivity to noise, but has the disadvantage of a long settling time of the pulses from the DCF77 transmitter. We could determine this time delay by comparing measurements of various receivers with an oscilloscope. It is considerably larger than the transit time of the signal from transmitter to receiver. In our clock it is 25 milliseconds. This value should be subtracted from the measured time.

Visor LED's of C14 Telescope

One LED of the visorThe light emitting diode may be adjusted by rotation and by pushing laterally in height. A second LED is located at 25cm distance. The power is supplied by two AA batteries and adjust the brightness with a potentiometer. The LEDs come with a lock pin plugs (protection from bend). During the renovation of the telescope, we have replaced the old LED visor by a commercially available red dot finder. Reason: The batteries had expired.

a electronic direction finder for the four-legged member of our team
the cat finder RANA, the four-legged member of our team gladly goes on long walks at night while we are working in the observatory. Towards the end of the observation then is the question often arises, "Where is the cat?". If after an observation weekend imminent departure and the train leaves according to the schedule in an hour, then this question can also be quite annoying. For these cases, we have developed 20 years ago a electronic direction finder for cats according to the pattern of bio-telemetry used in wildlife research. The RANA gets strapped on a backpack a small transmitter. This sends a short tracking signal every 5 seconds in the 70cm band. For radiolocation in close range caused an audible beeper. The search receiver has a special directional antenna with a very directional characteristic. This type of antenna is called HB9CV. Despite the smallest transmission power, the range is about 1km. Unfortunately we could not build the transmitter then smaller and lighter.

Nowadays, such devices on the Internet are available, applicable for pets and model airplanes and helicopters. Cats can use these devices on collar wear. The Cat finder Elpet developed by Mr. Ruedi Schenkel in Switzerland with digitally encoded transmission signal is a further development. Compared to other providers, it sends without interruption 1 year long with the same single button cell.

Workshop Tip: clamping of thin-walled tubes
 a internal thread must be cutclamping of thin-walled tubesthe three-jaw chuck usedIf thin-walled tubes are subjected to severe working in the so-called "flying clamping" on the lathe, then there is a danger that one flies the workpiece around the ears. The revolving lathe in the tailstock does not help always, if eg an internal thread must be cut at the flying end of the pipe. You might consider using as a lunette into consideration. Nevertheless, there is still the risk that the pipe at least slips in the chuck lathe.

Here a little trick. The experienced lathe operator knows anyway that in such cases, the pipe must be clamped together with a nuclear disk. Their own production we can save ourselves if we instead use a second lathe chuck in miniature design. This is placed inside the tube and clamps itself against the inner wall of the tube. Just in those three places where the small lathe chuck attaches inside the jaws of the large lathe chuck clamp on the pipe from the outside. As can be seen in the figure, the aforementioned internal thread at the other end of the tube can be produced without problems.

The workpiece shown is a new eyepiece tubes for the over 100 year old 12 "Alvan Clark refractor, in the west dome of the University Observatory in Vienna, produced for the amateur group.

Observatory maintenance

2012 new entrance to the large observatory

On the observation terrace is now leading the way to the observatory. You're coming to the telescope via a small bridge. Both the steps and the platform in front of the door of the observatory made ​​of steel gratings. You is sure-footed and the stages remain mostly in the winter snow. Access to the equipment room under the bridge is now possible at any time. The material was supplied by Steiner from Purgstall prefabricated according to our measurement method. Adaptation and assembly was done in self-made. This is facilitated by the use of aluminum extrusions with T-slots. This version allows even the subsequent change of the stair slope between 40 ° and 60 °. In order to adapt also the banister staircase to the changed slope, had to be changed his pipe bend. Christian K. from our team perfectly mastered the technique of hot bending of aluminum tubes and posing proudly in front of his work.

Red light mode for PC monitor

The PC monitor next to the telescope affect any visual observation by its dazzling. After red light software has proven to be insufficient, we were looking for a hardware solution for the problem and found. The following PDF Reader filereport describes both "electric" and a "visual" solution, which we have preferred the latter. (currently only available in German language)

oberver dome for 50cm RC
the dome All "Astro-nomads" who want to be with their Hobby "settled", will also need a protective building for the telescope. At least with advancing age of the Observer if you feel the intervertebral discs, you're glad to have a Observer dome. You do not want more mount and remove your telescope from the tripod. Here we show a protective building that can even grow with the telescope within certain limits. It was certainly a long way from the original version kept very simple (see two images below Historical) to today's high-tech observatory. Not everything we would do it again today. So it is recommended that the position of the foundation pillar plan for the ultimate telescope mount. The fork mount needs a different position than the German mount. In this PDF Reader filejournal article not only plans and design details of our observatory are shown, but also fundamental considerations and comparisons made between the various forms of telescopic protective buildings. The automation of the dome drive is described PDF Reader filehere. Spherical panoramic images of the inside of the observatory see here

observer dome air conditioning
Compressor unit of the air conditioningDIY control unit They should ensure the temperature of the telescope before start of observation. Moreover, they can also to dehumidify the dome space and an alternative to the supply of process cooling (cooling water) are used for focal-plane instruments. This versatile, partly self-built plant was designed in collaboration with a company for refrigeration specifically for the operational requirements in an observatory. Models can be found in many new or modernized professional large observatories. Once enough are present practical experiences, we want to introduce concept, construction and application in more detail here. PDF Reader filemanual

wireless sensors for climate values
Data Logger WS2500PC and battery-powered temperature / humidity sensor. 70cm transmitter and receiver module In order to gain empirical data for the optimal adjustment of our dome air conditioning, there are now several measurement sensor for detection of temperature and humidity. The temperature of the large primary mirror is measured directly on the mirror and can always be compared with the indoor and outdoor temperature. The goal is to minimize the usually necessary cooling of the telescope by the use of the dome air conditioning. By detecting the moisture in the mirror cell and the dome interior, it is possible to avoid dew in the dehumidification mode. Other sensors are the same for cooling in the icebox of the "big air dryer" and the new 20 liter cold water tank next to the immersion evaporator of the air conditioning. This plant will be used in the future for secondary cooling of focal instruments. The electronics of the CCD camera 2 can be monitored for temperature and humidity for safety. All values are measured by commercially available partially converted Wireless weather station sensors and sent to a independent working datalogger. Via a serial RS232 interface the collected data can be queried and sent for analysis to a PC. We hope this information to be able to optimize the use of the dome air conditioning. To be continued.

wireless weather station
Weather station solar sensors and Meteosat antenna Converted sensor for measuring the night sky brightness and rain funnel to measure the conductivityThe measurement technique originally intended only for the optimization of the dome air conditioning was expanded to a complete wireless weather station. On a stainless steel-made antenna mast itself several commercially available sensors for the detection of wind, rain and daylight brightness are now mounted. Solar back up power supply. During the day, they load on backup batteries, which also ensure the function at night. The data transmission is by radio on the 70cm band, fed from double-layer capacitors for energy storage. Another such sensor was rebuilt. Now, instead of the temperature and humidity he detects the brightness of the night sky and the electrical conductivity of the rainwater. The very simple circuit to itself has been developed and has already been copied. To be long-term studies of the artificial sky glow at night, the so-called "light pollution" is possible. To display serves a weather station type ELV WS3000TV. A total of 21 readings with their trend curves of the last 72 hours are available on the TV screen. Previously, the station added our Meteosat receiving system, which provided us many years with current weather Satellite images on the TV screen. Now we get the weather images from the Internet. The densification and continuous archiving of all data in the PC for the purpose of long-term studies assumes the data logger described above.

For the measurement of light pollution we are now connected to an international network, with standardized instruments, the so-called Light Meters

automated obserber dome tracking
Screenshot for dome trackingThe "dome", the rotatable roof of our observatory is driven by a self-made screw-angle gearbox of a three-phase motor. This three-phase motor is connected to a commercially available small inverter (nowadays a cost effective solution off of what is offered in the Astro equipment trade). Speed and direction of such a drive can be easily controlled with two push-button switches and a potentiometer on the wall. For the dome rotation we have provided two speeds: a very slow rotation for tracking the dome in accordance with the tracking of the telescope and fast rotation for the orientation of the observation gap at the entrance aperture of the telescope, after the telescope has been positioned for a new celestial object. The rapid dome movement, ie the orientation of the observation gap on the entrance aperture of the telescope after its positioning on a new celestial object you doing still manually (later we also automates, see below article). The slow rotation for tracking the dome are you doing under computer control with software from us.

After it is even the slowest rotation speed with the inverter still too fast for one sidereal tracking, we just do what you'd do well with a manual dome: We operate the dome drive only temporarily. Every 10 minutes, the computer determines the new azimuth of the selected object in the 50cm-RC and puts the dome motor short time to move to the open dome gap on the line of sight of the telescope realign. A technical measurement and feedback of the dome position to the computer is not necessary in this method. At a constant rotational speed, the duration of the dome rotation is proportional to the rotation angle. The angle of rotation in turn corresponds to the required azimuth difference. The speed ramps of the inverter (soft start and stop) do not play a role in the minimum speed. So we can computer control the duration of the switch-on interval set proportional to the rotating azimuth difference, which arose after 10 minutes due to the Earth's rotation. The proportionality Angle_of_rotation/time is determined once the stopwatch and go as parameters into the software. Mechanically induced errors on this consideration, all add up after a long time to be noticeable differences. They can be neglected: If we re-align manually the dome gap at each repositioning of the telescope, these errors fall away. The control of the inverter is via USB card (kit K8055), which has taken over the same time, other control tasks as part of our observatory control system (focusing, fine movement). The Windows software has self-developed.

Is the way, who believes that the dome tracking only one of the two possible directions of rotation required (from east to west) is mistaken. There are regions in the sky, as the dome for tracking must also turn in the opposite direction. That with the "slow speed", however, does not apply to follow-up through the Zenith. In theory, can be infinitely large, the speed here. Practically, one right Observatories domes in the zenith at each rotational position the view of the sky free, so does not need to be rotated.

automated observer dome positioning
Screenshot for dome positioning Even once we have dealt with this issue. The tracking of the dome described above worked without a dome position detection. Back then it was just concerned with the annoying turn of the dome during an ongoing CCD image to be run by the computer. The accuracy of this procedure has completely enough for a purely sidereal tracking of the dome, but not when the telescope is slewing to a different region of the sky. Now we change that with a self-developed measurement technology detection of the dome position: Once the telescope has a new goal now dome and telescope set in motion at the same time (sometimes even in different directions) and take a short time later at the destination. Also the speed of the dome we change now with the software. Our control also controls special cases that go beyond the capabilities of other dome controls. More detail is provided in a PDF Reader filetechnical report. This automation is a further step towards the mode "Remote Observing".

minimization of heat load
control consoleWith a telescope aperture of 50 cm you have to avoid all sources of heat in the dome space emit more than a few watts of power to the ambient air. In one corner of the dome, the PC workstation to service the telescope and Focal is instrumental. To keep the heat in the dome space as small as possible, the computers are relegated to the small equipment room below and the previously used CRT tube monitor (80W) replaces (15W) with a 15" TFT flat screen. The screen and a new keyboard with switchable illuminated buttons are connected together with the mouse over an electronic switch with the relevant computer (telescope control computer or camera control computer). A switchover takes place via hotkey (shortcut key). Tests have shown that a fault-free operation of the display is also possible at -18 ° C. In the picture above visible, the elegant semi-circular foot free corner table is homemade. At this workstation, we take the whole observatory technology in operation at the beginning of the observation. Upon visual observation you are doing well as the positioning of the telescope and the dome rotation. In photographic observation we no longer need the workplace, since we use remote operational from the control room in the house. To monitor during pivoting of the telescope, the drooping camera cable, air and coolant hoses you have 2 video cameras to control and can avoid the tangle cable with it. Installation of the vent pipeThe small equipment room below the dome room was equipped with a powerful hot air exhaust. A sewer pipe with 25cm diameter drawn from heated room air in a nearby basement with the help of a powerful fan (he comes from the radiator of a VW car). The heat comes from the devices (computers, telescope servo amplifier, dome drive, cooler, etc.). In this basement room also housed our dome air conditioning compressor. In this manner any air heated by the telescope is kept and can thus no longer affect the seeing.

remote control with two monitors
the two screens Over a network cable the house is connected to the observatory buildings (one could also via WLAN achieve the same). This is not only possible to access the data of all computers in the network, but also mutual remote control of the computer to one another using VNC program. This remote access freeware is used commercially for remote maintenance of servers via Internet. The remote-controlled programs do not need special properties, almost any existing Windows program can be controlled remotely. Contrary to the assertions of the company Software Bisque (and other providers who want to astronomers persuade only their own products), there is in the way general remote access freeware no additional problems with the data security and the alleged problems in terms of performance is limited to: a slower response of the mouse pointer and small delay in updating the screen. Only the remote software from Microsoft itself has given us occasionally causes problems, but you do not even have to use.

In this way, we control everything about our self-programmed observatory control system from the "living room". The recently applied client-server architecture of the PDF Reader filetelescope control system offers a degree of safety in the operation from a distance. Both the correct execution of a remote instruction and technical problems as in case of failure is reported back to the control system and visualized by this. This functionality is complemented recently by a PDF Reader fileremote logging tool and a PDF Reader filevideo security system. Previously, we had yet again out into the cold to rotate the dome. Today also this function is fully automated, PDF Reader filesee-here. Only the opening of the dome we must have still done manually. It can not be automated, for mechanical reasons. Global control via the internet is not intended currently. (all articles currently only available in German language)

The absence of people in the dome room, the heat load is reduced even further and improves the seeing. The computer in the living room is now a particularly power-saving model (ASUS EeeBox) with ATOM processor. This little computer has a power consumption (measured by us) of only 12W, with no external USB accessories. It operates silently and is also suitable for the operation around the clock. If required, an external graphics card (USB to DVI-VGA-HDMI adapter of Delock) is connected to a second screen. Up to 6 screens would be operable in this manner. Star chart, operating window of the control system and recorded images from the observatory can be next to each other is clearly presented on multiple screens.

sliding roof observatory
sliding roof observatory A small protective building, ideal for commercial SC telescopes. Despite their small size is sufficient space for the Celestron C14 on an old German mount (Sideres). The specifics of the design of the roll-off roof are described in the following PDF Reader fileArticle. A spherical panoramic image of the inside of the observatory as well as more pictures click here. Currently, the second observatory is rarely used by us. It is available to selected visitors. A revision of the mount is complete. Later, maybe they should be equipped with pre-existing, high-resolution angle encoders. After a more suitable control (which also meets our high standards) is still being sought. The optics of the C14 should be subject to revision: Here the conversion of the secondary mirror cell is planned.

observer dome dehumidifier

For smaller devices (such as our C14 in the rolling roof building) to prevent in most cases dew formation on the device, it suffices to pull over a solid bag. Thus prevented a too rapid warming during the day. That would be too cumbersome with our large 50cm RC telescope. The mass of the telescope has a significant heat capacity. This results in a rapid rise in temperature to excessive formation of dew on telescope. Although the moisture can not penetrate the sealed mirror cell, but woe to open the mirror cover. It is therefore advisable to keep the whole room dry. Corrosion on the telescope is suppressed. We use a commercially available air dryer from the hardware store. This device works like a refrigerator with automatic defrost. In the defrost cycle, the compressor turns off for a while. At low temperatures, the ice thawed but not from the evaporator during the defrost phase. We have therefore attached a defrost heater to the evaporator. This consists heating cables 1.5m eaves, which is powered by a 12V transformer for halogen lamps with about 70W. A heating thermostat ensures that the defrost heater is activated only at room temperatures below 3 degrees. Since the completion of the dome air conditioning our dehumidifier is used in the small observatory.

Alternatively, you can the telescope dry in the sunshine during the day with solar energy: The dome slit is opened for this purpose and our dome control described PDF Reader filehere, the dome tracks the sun all day long, while the telescope itself is not in operation.

computer cabinet heating

computer box Heater below the computer Base plate with heater heater element from a hairdryer Turning on the computer in the observatory at temperatures below zero may cause problems when booting the hard drives. For this reason we have built the computer in a box that temporarily controlled with a heater (hairdryer) is preheated. After the preset time, the heater turns off and the computer can boot. Then the computer generate enough body heat to keep in a closed box, the required operating temperature. In summer, the heater is turned off and the box door remains open. The computer cabinet is located below the dome space in its own small equipment room. The heat sources are kept away from the telescope. Only the screen, keyboard and mouse are housed in a corner of the dome space, and can be assigned to each machine via switch. They work flawlessly, even without pre-heating at low temperatures.

Alternatively, you can try to find a cold-resistant computer. Test several hard drives at low temperatures, or use solid state disks to boot. Swap out all the components that make the problems at low temperatures. Industrial computer with extended temperature range are not assembled differently.

dome-rotary drive

If one pays attention to the electric drive when you visit a dome observatory, is usually found a gear motor attached on the rotating ring, which disruptive protrudes into the dome interior. If you press a button, then the dome is suddenly set in motion. We managed to avoid these two rod and toothed beltselfmade worm gear

Mechanical design: Appropriately uses a ball-bearing rubber roller for the drive on which resting the rotating assembly of the dome with a part of its own weight. We use a total of four support rollers. The three non-driven support rollers are made of iron pipe with inserted ball bearings. You have to be strictly observed in this division of iron rolls and rubber roll, using only rubber rolls is completely false. In this way, unnecessary flexing is avoided and the approx 300kg heavy dome is easy to turn. If you have used rubber roll anywhere, you'll have the dome can barely turn. To the driving roller a homemade worm gear is attached. A claw coupling the worm is connected to a vertically arranged drive rod. In this way the drive motor can be installed under the ground. A toothed belt provides the necessary distance of the motor from the wall. So nothing protrudes into the domed room inside where you can kick off your head.

three-phase induction motor inverter housing

Electrical design: We use a 4-pole three-phase asynchronous motor (induction motor) with 125W. This is supplied with a small inverter from the single-phase 230V here in Europe. Harmonics generated by the inverter could interfere with sensitive measuring instruments (photometers or CCD cameras). That is why we have good line filter mounted in front of the inverter and made a double shield of the motor cable. Leave you no other drive to persuade when you have power grid connection. Without electricity network connection with batteries use direct current motors.

Realized Effect: The dome rotation speed can be infinitely adjusted from the "Slow speed" to the "carousel", in each case with gear gentle soft start and soft deceleration. Frequency can usually quite easily be controlled by the computer. We have now developed a PDF Reader filefully-automatic dome positioning and used successfully. (currently only available in German language)

Flatfield light box

the new version with single light source and optical fibres inside the light box (original state) the light box the light box mounted in our observer dome For image calibration of CCD images of a uniformly illuminated surface, so-called PDF Reader fileFlatfields are required. We provide the flat field images just using a light box in the observatory mounted. It depends on the uniform illumination of the light box, also depend on the spectrum of lighting. While for simple amateur CCD cameras (eg SBIG or Starlight Xpress or DSLR) is sufficient a discrete spectrum, the requirements for high-sensitivity, back illuminated CCD's are already higher. Here you need the continuous spectrum of a black radiation equipment. We had to equip the lighting of our PDF Reader filelight box in addition to optical fibers. The light source is now a single halogen lamp.

(currently only available in German language)

A very small planetarium

the mini planetariumthe mini planetarium In the age of planetarium programs on your home PC seems to have a real small planetarium obsolete. But the impression to see a spatial reproduction of the whole heavens, remains one denied by the flat screen. Even if the sky is only printed on the small dome of our self-made planetarium, for the one who puts his head under this dome, the effect is still amazingly real. It can be adjusted to the sight of heaven for latitudes from 50 ° N for each day of the year. Of course, planets can be represented by adding them with 2 small magnets. Place this planetarium at night on the lawn, you need only to make a single step aside in order to compare the stars in the dome of the mini-planetarium with the stars in the sky. For this you can the stars light up effectively in the planetarium. You can reach this with an indirect illumination by UV light. For this purpose we have assembled the horizontal circle with dimmable UV Leds. The printed stars fluoresce with this lighting. The planetarium dome itself is a commercially available kit from cardboard. By painting with clear coat do you do it suitable for outside use. You put the dome just on the horizontal circle. Here you count in the date and time correctly. This horizontal circle is our idea. Operation and construction are described in detail PDF Reader filehere (currently only available in German language). We want to use this planetarium for visitors to learn the constellations in the sky.

planetary trail

The planetary trail serves to demonstrate the size relationships in our solar system. The sun is symbolized by a yellow Styrofoam ball of 20cm diameter. The planet for our path are painted on laminated A4 sheets at a scale of 1 to 7,000,000,000, together with the orbits of its moons. The distances to the neighboring orbits of the planets and the Sun are indicated on the panels. The sun ball and planetary tables have a 1 m ground rod made ​​of stainless steel. In this way the Planet can be set up along the way from the Sun to Pluto within one kilometer quickly.We have used the path at visit by elementary school classes.




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