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Astro-Tech 10" RC & SBIG 8300

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#1 Bill W.

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Posted 10 May 2013 - 06:49 PM

Is anyone using a Astro-Tech 10" RC and a SBIG 8300 w/8 position color filter wheel or something similar in weight? I was wondering if those people were experiencing the sag/collimation issues. I am interested in the AT10RC but that is my biggest reservation with the scope. It would complete my scopes for imaging rather nicely... :D Thanks!

-Bill

#2 pfile

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Posted 10 May 2013 - 07:24 PM

that's me

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.

#3 Bill W.

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Posted 10 May 2013 - 08:40 PM

That's what I am worried about. I hate chasing my tail with issues like that. The skies aren't clear around here for weeks at a time. I thought I read where someone was making a plate for the back to help stiffen everything up some.

-Bill

#4 pfile

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Posted 10 May 2013 - 08:50 PM

well the problems are surmountable, but i guess "you get what you pay for" applies here. these scopes are really cheap compared to the competition... as such you will probably have to put in a little sweat equity. well and some actual equity since many people consider the stock focuser to be inadequate (though there are those that think it's fine). i have not yet invested in it, but the teleskop-service tilt/tip ring seems to be an essential tool for really collimating this thing properly. more $$$ :)

#5 Bill W.

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Posted 10 May 2013 - 09:02 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!

-Bill

#6 jrcrilly

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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!

-Bill


If you go with the Moonlight, I believe the focuser includes collimation adjustments.

#7 Bill W.

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Posted 10 May 2013 - 09:34 PM

Thanks John. I would go with Moonlite. He's not too far away from where I live and makes a great product.

-Bill

#8 Jared

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Posted 11 May 2013 - 12:01 AM

I have one of these RC's that I have been using with a FeatherTouch focuser and one of the adapters ensure the focuser is square. I have used it with ab SBIG STL series camera (heavier than your 8300 camera) and with an FLI Microline (lighter). It took some careful work collimating, but I did not have a significant problem with flexure--and that was with the STL which would pose more of a challenge.

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.

#9 Jared

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Posted 11 May 2013 - 12:03 AM

A flattener is a requirement for chips larger than the 8300. And is a "nice-to-have" even with an 8300 based camera. The only way I could get sub 2" across the field was to focus 1/3 of the way out from the center of the field.

#10 pfile

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Posted 11 May 2013 - 12:34 AM

re: the teleskop tilt/tip, if i remember right sl63amg (photon) believes that the TS ring increases the stiffness of the mirror assembly by virtue of the fact that it's providing some tension when it's in place. so it might provide some benefit that the moonlite itself can not.

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.

#11 Jared

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Posted 11 May 2013 - 09:58 AM

I will also add that I would NOT recommend using the rotation feature of any of the common focuses with a long focal length scope like the AT10--Feathertouch, Moonlite, or stock focuser. Just leave the focuser rotation locked down. Moving it is enough to screw up your orthogonality a little bit--enough to be visible in your images. That could also be contributing to what some people report as sag in the system.

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).

#12 Bill W.

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Posted 11 May 2013 - 10:16 AM

Thanks guys! Jared, I've read some of your posts on the RC. Your post are what has made me reconsider the scope as being doable. I never rotate my camera so that won't be an issue. What focuser were you using? 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 ended up buying a self centering adapter and it works somewhat better. I would still prefer the t-threads. If you can get good images using a STL I am very encouraged to possibly be able to get decent results from my 8300.

-Bill

#13 Bill W.

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Posted 11 May 2013 - 10:30 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!

-Bill

#14 jrcrilly

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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.

#15 Bill W.

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Posted 11 May 2013 - 10:10 PM

Thanks John. I'll have check out my Moonlite.

-Bill

#16 Jared

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Posted 12 May 2013 - 09:34 AM

I have the Feathertouch 3" focuser on my AT10. In my case, I had an Astro-Physics flattener for my AP130 that I wanted to use with the AT10, so I bought the FT 2.7" adapter so I could thread in the flattener. I already had a custom adapter to mate the STL camera to AP flattener. Interestingly, I found that I shouldn't thread the flattener on all the way or it would mess up orthogonality (seeing a theme here?), so I need to thread it on most of the way and then use the AP lock ring to tighten things down.

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!

#17 Jared

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Posted 12 May 2013 - 09:49 AM

One other thing I will mention that you probably already realize... Unless you have better than average seeing conditions, you will likely find the 5.4 micron pixels are somewhat over sampled on this scope. You're going to be getting something like 0.54 arc seconds per pixel. This would be great for 1" or 1.5" FWHM seeing conditions, but is slight overkill at 2" or worse. Not a major issue, but you should be aware. You may find that binning 2x2 actually yields better results on most nights (though I'm not certain how well the 8300 works binned--I recall some issues with micro lenses when binned).

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.

#18 Jared

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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!

-Bill


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.

#19 Bill W.

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Posted 12 May 2013 - 09:01 PM

Thanks so very much Jared for your time in posting your experiences with the scope. It is appreciate! I will no doubt end up getting the AT10RC. I will usually do some research and decide on what I want. Then, think about it for a bit and come back and rehash through the details. I'm very much not an impulse buyer. I am a very methodical person so I do think I can overcome this scope being finicky because I am the same way... lol. I do plan to go with a threaded attachment point for the camera to the focuser.

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... :D 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!

-Bill

#20 Jared

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Posted 13 May 2013 - 11:30 AM

You should do fine guiding with the 8" or the new scope--just expect to work through a few kinks. The CGE Pro is a nice mount. With either scope, I'd recommend OAG rather than guide scope.

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.

#21 Bill W.

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Posted 13 May 2013 - 05:28 PM

Thanks Jared. I figured I'd probably have to go to an OAG. The 8" f/4 guides great with a guidescope but it's only 800 mm.

-Bill

#22 Roy Salisbury

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Posted 20 May 2013 - 11:58 AM

I just got my AT10RCF a few weeks ago and this last weekend was my "first light" with the scope. Initially the collimation was pretty far off (relatively speaking) and I got a Hotech SCA laster colimator that other said would work... but that failed. So I did it the old fashion way of defocusing the star and doing it visually. While not really spot on, it was better then what got shipped. Initial images were ok, but I know it needs a lot more work.

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.

Roy






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