Astro-Tech 10" RC & SBIG 8300
Posted 10 May 2013 - 06:49 PM
Posted 10 May 2013 - 07:24 PM
collimation issues, yes. probably you can't get perfect collimation at all OTA angles due to sag. check my astrobin for what i've done with it so far. OAG is a must in my opinion.
Posted 10 May 2013 - 08:40 PM
Posted 10 May 2013 - 08:50 PM
Posted 10 May 2013 - 09:02 PM
Posted 10 May 2013 - 09:10 PM
I think Astronomics is selling those tip/tilt focusing rings. I knew the focuser would probably need to be replaced. I'm spoiled by automated focusing.. lol. Thanks!
If you go with the Moonlight, I believe the focuser includes collimation adjustments.
Posted 10 May 2013 - 09:34 PM
Posted 11 May 2013 - 12:01 AM
I know some have complained that maintaining orthogonality is a problem because the primary is not attached to the back plate, but I didn't have any issues. I did have a problem with the fact that the system has no adjustment to ensure the focuser is square to the optical axis, hence the adapter from Teleskop Service in Germany. I understand you can skip this accessory if you get a Moonlight focuser since an adjustment is built in.
I found the scope to be a good value, and I was able to get sub 2" FWHM stars across the field of an 8300 chip without a flattener.
Posted 11 May 2013 - 12:03 AM
Posted 11 May 2013 - 12:34 AM
ram's recent thread about using a howie glatter collimation laser on an ATRC includes some comments from some that think it's too easy to accidentally rotate the moonlite, which will really upset any collimation adjustments you've done.
i can't really speak to either as i don't have the TS ring, and have not tried to collimate my moonlite. hopefully it's straight on from the factory.
having said all that, i know i still need to refine the collimation of my setup.
Posted 11 May 2013 - 09:58 AM
If you need to rotate your camera to find a guide star, do it with the camera mounting itself (which will vary from camera to camera--I strongly recommend threaded adapters at longer focal lengths, not just a 2" nosepiece).
Posted 11 May 2013 - 10:16 AM
Posted 11 May 2013 - 10:30 AM
Posted 11 May 2013 - 02:07 PM
I prefer attaching my camera by t-threads whenever it possible. That's probably my only complaint about the Moonlite I have on my 8" f/4 scope I have. It's a 3 point compression ring.
I know that all current drawtubes for their 2.5" focusers offer threads at the drawtube end; I think the 2" models may as well. It's not a T thread but it provides a square and solid attachment so you can go all the way to the camera with appropriate threaded fittings. I use a self-centering T adaptor with my older Moonlight.
Posted 12 May 2013 - 09:34 AM
In general, I would not recommend my AP flattener with this scope. While it is a good match as a flattener, it uses all of the available back focus and then some--I had to actually bring in the mirror spacing slightly past the optimum value to reach focus. This introduces a small amount of spherical aberration, but not enough to matter (I only needed a few extra millimeters). Most field flatteners do not use up so much back focus, and so would be a better match.
I would definitely recommend something threaded rather than compression rings. If you can't find something stock, Precise Parts can put together exactly what you need. They do very nice work. The 8300 has such small pixels, and you are working at such long focal lengths, that you need everything just right to avoid obvious astigmatism in all four corners. Based on my experiences with a much larger chip (and with an FLI ML8300) it is very doable, though. I found I needed the TS tip/tilt plate with the larger camera, but probably could have gotten away without it with the 8300.
Honestly, I never had problems with the focuser/imaging train sagging. It is a finicky setup, though (as is anything at this focal length), so you need to get the compilation right and make sure everything is rock solid from the back plate out. I even, at one point, had an issue with my FLI filter wheel messing up the orthogonality of the camera because one of the holes attaching the back cover wasn't machined out quite far enough and a screw head was sticking out a fraction of a millimeter causing the camera to be slightly "canted" rather than seated properly in the dovetail. That one took a while to find!
Posted 12 May 2013 - 09:49 AM
Best of luck! I think this can be a really good imaging setup for you. Just don't expect everything to be perfect right out of the gate. Imaging above 1,000mm focal length requires careful adjustment and optimization to get good results. That's why I cringe a little every time I see a new imager starting out with a 12" SCT on a fork mount and wanting to know what accessories they will need. Long focal lengths are finicky.
Posted 12 May 2013 - 09:57 AM
One other related thought... would a Howie Glatter laser with the holographic grid pattern be useful with the RC? I have read some on the collimation of the RC about the hall of mirrors... Thanks!
I have one, but don't find the holographic projector particularly useful. I prefer to just use the regular spot. Your mileage may vary, though. I use a Cheshire and the "hall of mirrors" reflections of secondary spiders to get the primary and secondary collimated, then use the laser return spot to ensure the focuser is square to the optical axis. Final tweaks under the stars.
Posted 12 May 2013 - 09:01 PM
Yes, I did realize that I would be oversampled by quite a bit for my area. I planned to try binning at 2x2. I have imaged at 1750mm before and know the challenges that lay ahead. My setup was different when I imaged at 1750mm. I used a LX200 10" f/6.3 w/AO7. The DEC drive on my LX200 was dying back then. But, I think my current setup will outperform my old one. I have a CGE Pro now. I moved three years ago. Now, I live at the base of a mountain, which at this point, is my biggest concern. I do have a 8" SCT that I plan to use to test out how doable guiding at 2000mm is here. I usually get around 2.6-3.0 in FWHM. How flat is the AT10RC?
I have a cheshire/sight tube and laser. Does the tak collimating scope have big advantage over regular collimation aids? I'll be burying myself in reading up and understanding RC collimation before I get the scope. I have a 8" f/4 newt that can be pretty finicky. But, most of it's issues are tube flexure because my camera and filter wheel are heavy and the tube would flex. The tube would flex enough just slewing to different angle that you could see it easily in the images. I just replaced that scope with a carbon fiber version with the same specs... I'm waiting for clear skies to put it through it's paces. I think the RC will round out my imaging scopes nicely. Thanks again for your time!
Posted 13 May 2013 - 11:30 AM
The AT10RC is flat enough that I would consider a flattener "optional" with an 8300 sized chip or smaller. You'll be able to detect an improvement with a flattener, but you can certainly get away without one. It's on the edge of acceptable, though.
I haven't used the Tak collimating scope so can't speak to its effectiveness. I can tell you that it isn't required, though. Your cheshire and laser are sufficient. Ritchey's are finicky about collimation, but the AT tends to hold its collimation well so I wouldn't expect a problem with just the tools you have.
Posted 13 May 2013 - 05:28 PM
Posted 20 May 2013 - 11:58 AM
I'm not using an SBIG model 8300 on this scope, but rather the QHY9m (but its still an 8300 based camera). I may switch my STT-8300 over to it and off the AT106.
I'm hoping not to have to use an OAG because I have never really had good luck with them. Instead I am going to use my AT106 (704mm FL) as the guide scope. Its a good solid mount on a Paramount MX, and the only thing I will need to watch for (hopefully) is sag in the image train between the two scopes.
Anyway, just thought I would put in my $0.02 on this scope and camera option. I think I will really like it once I get it setup properly.