Here I reflect on the learning after over 1000 hours of observing and over 6 months at DSO operating remotely.
- The computer system, remote switch and all the electronic has worked flawlessly, 100% availability. Remote update of Windows, software… have also been painless. I have used Google Remote Desktop exclusively, without any worry.
- I have had one mount loss, and recovered manually in about 30mn. The fact the mount has no encoder (absolute or otherwise) is a total non issue, and for future remote setup, I do not think I will need absolute encoders unless I get into asteroid/satellite tracking, which would, by the way, also necessitate a fork mount (to do away with the meridian flip). To the specific of the mount loss: it is due to a bug in APCC Pro. APCC Pro should just be extra features on APCC. However those are 2 different software than can (but should never) coexist on the same computer. I had been using Pro for a while, but one evening I had not started the mount software before hand, so when I launched NINA it auto started APCC (rather than APCC Pro). As those 2 software do not share the mount position file, APCC used an old and incorrect mount position file, not consistent with physical reality. To regain internal consistency, APCC then proceeded to corrupt every possible setting: time, observatory position, scope position, etc.. without any warning. Even the side of the pier was incorrect. To recover, I moved the scope using manual controls, looking at it on surveillance camera. This is dangerous thing to do as this can lead to a pier collision and possibly twisting of the cables going through the mount. However I managed to move the scope to the sky, without collision and without inducing twists (I checked months later). Then once looking at the sky again I blind solved and resync the mount. The irony is that then APCC Pro’s safety checks (which had left me down in the first place during the crash) kicked in and prevented the recovery (error between solved and expected position too big). The quick solution is to iteratively add a series of corrections, all under the safety threshold, then do one last plate solve. A major problem with this procedure is that the mount can be told its true pointing position (Dec, RA), but not the physical side of the pier it is on (and each pointing direction has 2 sides of pier possible). The solution to this second layer of problem is to move to Park 3 (ie: looking at Polaris in the Northern Hemisphere) and cycle the mount, restarting from Park 3. Since I have uninstalled APCC and things have been going well – no more lost mounts.
- Mount: tracks below 1 arc sec most of the time. The added counterweight to reduce the inertial moment helped a lot. Read this if you need the full explanation.
- Data sharing: I use syncthing, a very light and efficient system. This works flawlessly.
- Collimation: for the longest time I could not decide if I was more a laser “Glatter” or Catseyes kind of guy. I am now definitely on the Catseyes Autocollimator side, and I follow instruction on the highly recommended Vic Menard “New Perspectives on Newtonian Collimation“. My rational for this is: if anything anywhere is wrong, you do not get an autocollimator read – so at least you know. Correlatively if you get a good autocollimator read, you are aligned. By day and by night.
- Wind: big Newtonian tubes are very sensitive to high wind pushing on the tube and messing with guiding. It is just a fact of life and maybe I did not fully measure this drawback when getting into the project.
- Camera: My current 1600MM is just not doing justice to the scope and the observatory conditions. I am moving to a QHY 168M.
- Collimation stability. This has been the main problem I experienced on my setting. I indulged some musing on the topic on CN forum , and here is the gist of it: I have a Newtonian Astrograph using a thin (.78 inch) Zambuto 10″ fused quartz parabolic f/4.5 mirror. The mirror is supported by an Aurora Precision EQ cell. The astrograph is located at DSO, operating remotely every clear night, all night. I have over 1000 hours of observing on that scope, in a wild variety of conditions. The imaging results from that scope can be seen here, while I discuss the optical design of the astrograph here and the mechanical design here. Further I distribute all the observation raw data open source here. Because everything is available open source for that scope, from CAD design files to the raw fits images taken every night, what I say can be verified with actual available data, and if I err, people can call me on that (and some certainly have). For completeness: I collimate with Catseyes autocollimator using the Vic Menard “New Perspective” book. So to the topic at hand: currently my mirror is not glued to the cell. If I let the mirror pretty loose in the cell, I experience movements of the mirror (with an effect akin to a mirror flop in a SCT) when I track low on the horizon or when I park the scope head down. If I keep the mirror tight in the cell, I experience astigmatism -lots of it. If temperature was constant, there might be a sweet spot where the cell is tight enough to maintain collimation but without excess that would warp the optical surface. However, temperature at the observatory ranges from 0 F in the dead of winter to 100 F in the Texas desert heat, so this sweet spot does not exist. So for me thin mirror + EQ Aluminum cell + not gluing is not working. To be fair, if you do not park the telescope inverted, do not track low on the horizon and have access to the scope to tweak collimation every evening before your observation run, it probably works just fine. Another problem with the cell & not gluing is the need for clips to the front of the mirror which degrades the image, as documented here. Maybe not an issue for visual, but definitely a problem for imaging. A solution may be to do away with thin mirrors, but then I would suggest to go all the way down that road with “conical” mirrors like Royce used to make for Newtonians. After all this is how Planewave does it for this size of mirror (photo here) on their astrographs and those are very stable in all positions. Now let’s say you already own one of those thin mirrors and want to support it properly. This is a very difficult problem I am afraid. Currently I am building a new carbon fiber cell, and will silicon the mirror to it. The mirror will also be siliconed to the edge support, and there will be no front clip. I plan to post the CAD design when done and tested. The rational for Carbon fiber comes from the CTE comparison (Coefficient of Thermal Expansion): Carbon Fiber (30 × 10−7/K) Fused quartz (5.5 × 10−7/K) Aluminum (240 × 10−7/K). For CTE calculation of Carbon Fiber and anisotropy discussion, see here. I am also exploring the possibility to glue a conical piece of glass to the back of the mirror, so it could be supported like a conical mirror.