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

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 report (currently only available in German language).

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.

Southwest view	Northwest view	dome inside	control 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

:

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):

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 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!

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.

Fig.1 Erich Kowald in his dome	Fig. 2 finished 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 painted	Fig. 8 test Setup workshop	Fig. 9 test Setup workshop	Fig. 10 test Setup workshop	Fig. 11 Remote control DIY electronics

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

The 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 RA bearing RA-gearbox	fork RA-frictionwheel	central part of optical tube	gearboxes behind RA front DE	Newton mirror cell	Newton hat	Newton mirror

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.

optical tube without counterbalance	optical tube with counterbalance	optical tube with diagonal mirror	optical tube and instrument flange	optical tube with diagonal mirror	mirror cell	instrument flange
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 encoder	Servo motor encoder	a bigger encoder	clutch for encoder	flange for encoder	declination motor unit assembled
test run with Dr. Stoll	test run with Dr. Stoll	Stoll-type isa-bus cards	Dr. M. Stoll and Andreas Kreutzer	principle of servo controller

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).

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

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 http://www.starmystery.de 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).

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 here 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 .

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 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.

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.

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 here (currently only available in German language).

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 here (currently only available in German language).

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 report (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 here.

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.

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 here (currently only available in German language).

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

For 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.

In 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. 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

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.

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.

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.

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 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.

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.

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
  

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" .

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 here (currently only available in German language). To center our great RC telescope, however, more is needed.

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 here (currently only available in German language).

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 software 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.

After the renovation of the Sideres-85 mount, we need a sidereal clock again to use the pitch circle of the hour axis. A short report 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 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.

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.

However, 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.

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).

The tools required for the construction of the great telescope have already been listed in the specifications - section1. 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 - Report 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).

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.

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 here (currently only available in German language).

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.

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.

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.

The 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.

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.

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.

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.

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 report describes both "electric" and a "visual" solution, which we have preferred the latter. (currently only available in German language)

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

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.

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 telescope 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 remote logging tool and a video security system. Previously, we had yet again out into the cold to rotate the dome. Today also this function is fully automated, see-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.

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 here, the dome tracks the sun all day long, while the telescope itself is not in operation.

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.

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 drawbacks.

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.

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 fully-automatic dome positioning and used successfully. (currently only available in German language)

For image calibration of CCD images of a uniformly illuminated surface, so-called Flatfields 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 light box in addition to optical fibers. The light source is now a single halogen lamp.

(currently only available in German language)

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 here (currently only available in German language). We want to use this planetarium for visitors to learn the constellations in the sky.

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.