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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5542696 - 11/27/12 07:39 PM

I haven't actually used it but have friends who do very successfully. Whenever you use a moving mirror scope there's a possibility the mirror will not only tilt but will also slide back and forth ruining focus. With either internal or external focuser this can happen. It's important to check focus often with such scopes. FocusMax makes this easy and fully automated with proper software.

My LX200R is very sensitive to temperature changes. With an external focuser and fixed mirror not only does the focus change with temperature due mainly to a change in mirror spacing as the aluminum tube contracts in the cold. This changes the image scale. Something basic image aligning routines can't handle. A moving mirror system readjusts the mirror spacing when focusing so keeps the image scale from changing significantly. A plus for using the moving mirror focuser.

Rick


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Migelo
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Reged: 10/03/12

Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5545686 - 11/29/12 03:07 PM

Cool! This Robofocus seems rly cool! A lot of people say it's great. It was made specifically for LX200 so it can't do bad.

We'll be going with this option.

What about the OAG? The only one I've found that supports big chips is Monster OAG. Do you know any other?


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5545759 - 11/29/12 03:57 PM

Have you seen this?

http://www.sciencecenter.net/hutech/mitsub/oag.htm

Look for OAG-6. Also see this:

http://www.sciencecenter.net/hutech/mitsub/oag6.htm for KAF16803 CCDs.

I own a smaller version OAG-5 with optional helical focuser and it works great with my C-8 EdgeHD and Lodestar autoguider.

Many adapters are available with OAG-5 but I am not sure about OAG-6. Hutech's web site is not intuitive. Write an e-mail to them stating exactly your requirement and they will quickly respond with an answer you are looking for.

Peter


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5545905 - 11/29/12 05:50 PM

Other than using thumb screws for attaching (never trusted them) it looks like it would work and is cheaper. With my temperature changes they work loose all too easily.

Rick


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5545947 - 11/29/12 06:14 PM

I understand what you mean by thumbscrews. These thumb screws are pretty big and really tightens hard and very well. Hutech OAG allows to rotate for ease of framing DSO.

Another great feature of Hutech OAG is it's really easy to adjust the pickup prism up and down and allows you to easily position the prism so that the prism does not obstruct the imaging camera's CCD.

Peter


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5546004 - 11/29/12 06:46 PM

And it's 800€ cheaper, that's definitely a PLUS. =)

And if, let's say, those thumbscrews would get loose often, because of temperature variations, what are my options?

I wrote to Hutech and Apogee concerning adapters and Hutech responded if I know if that 3.25" thread is the same as on Celestron STC?


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5546041 - 11/29/12 07:04 PM

I believe Meade's and Celestron's 3.25" threads are slightly different. I believe that Celestron's 3.25" accessories can adapt to Meade's 3.25" scope but not the other way around. I know this because I sold my Moonlite focuser for C-11 which uses 3.25" to someone that has a 12" Meade with 3.25" rear cell. This person told me that accessories designed for Meade will not work for Celestron scopes with 3.25". Very very strange.

Peter


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5547892 - 11/30/12 09:13 PM

Very strange indeed!

All I can say right now is: Adapters, adapters, adapters and adapters!

Nobody (Apogee, Hutech and Meade) can't tell me if I'll be able to fit the OAG to the telescope and the OAG to the filterwheel.

In the end, the adapters will have to be custom made.


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5548049 - 11/30/12 11:33 PM

That's part of the problem with oversize openings at the focuser end. There isn't a standard for this. It's not as common as smaller openings like SCT or T-Threads. You may have to pay a bigger price for this but the rewards can be much greater by taking advantage of larger FOV.

Peter


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5548223 - 12/01/12 02:42 AM

Individual companies often don't know other companies gear but dealers that carry all of them often do. Check with Astronomics that hosts this site or OPT or other big dealer that carries these brands. Both have helped me find adapters when needed that individual companies couldn't.

Rick


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Hilmi
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5548281 - 12/01/12 04:33 AM

Astro-physics recommend these guys for custom adapters. Their site makes it easy to get what you need.
http://www.preciseparts.com/ppmain/adapterp.html


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Hilmi]
      #5549382 - 12/01/12 08:48 PM

Thanks for your suggestions!

Does anyone have any experience guiding a scope with a such large focal lenght? What kind of exposure time will I achieve?


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5549784 - 12/02/12 03:58 AM

I work at 3650mm and can expose a sub exposure as long as I wish but usually no longer than 30 minutes because it saturates too many stars.

It all depends on your mount. The Meade fork is not a great one and often needs an AO unit though some have managed to tame them. Most of my friends using them use an AO unit that moves a mirror or prism to make the fine adjustments their forks just can't manage. I use my LX200R on a Paramount. I fought poor mounts for over 50 years and decided enough was enough.

The learning curve however is steep. Most would recommend starting with a far shorter focal length scope say mounted atop the LX200 until you've mastered the basics before moving to 3000mm. Even though I had 50 years of manual and then automated guiding with film that was at 1200mm or less. When I moved to the Paramount and LX200R I first put a 600mm 150mm reflector on the mount to learn the differences from film. After several months of using that system every clear night I moved to the 14" f/10 without difficulty.

Sub exposure time should be sky limited if possible. That buries read noise in the sky noise. Once that happens there is little if any gain in going longer and you'll just saturate stars losing color differences. Dither many subs and align them then stack using a good sigma routine to remove noise and you'll have a much better image than a single exposure of the same total time would give.

The worse your polar alignment and the further the guide star is from your field of view, the shorter the sub exposure must be to eliminate rotation of the field around the guide star. A lesson I learned the hard way with film where one and two hour exposures were necessary. CCD allows you to break this up into many sub exposures greatly reducing the strain on the system to work perfectly for and hour or two.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5550326 - 12/02/12 01:15 PM

Meade fork?
AO unit?


I have experience with Refractors and Newton Reflectors, but not much with STC, so excuse my ignorance. =)

And yes, CCD imaging with stacking sure rocks!


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550538 - 12/02/12 03:27 PM

The LX200 can come on their LX200 fork mount or just the OTA and you supply the mount. You never said which yours is. Not willing to fight their fork I went the OTA route.

AO is adaptive optics. These units guide by moving a small mirror (smaller units than for your size chip can use a prism). Moving 100 grams of mirror rather than 50kg of scope and mount can greatly improve guiding accuracy due to less inertia. And if the guide star is really bright so you can use a 0.1" guide exposure it can even correct for slow seeing effects when used on a long focal length scope such as yours. Most use it for improved guiding of sloppy mounts. My seeing isn't of the type it helps and the Paramount can easily handle what very little guiding is needed due to its extreme accuracy I never went that way. However most I know using the 8" and 10" LX200 forks (no one I know has the 12") found they needed AO to tame them. One with a 10" has managed to tame his to his satisfaction. I don't know if an AO unit for the 9000 chip exists however.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5550591 - 12/02/12 03:50 PM

I have meade fork mount permanently attached in the observatory.

And I've decided to go with the Apogee F16803 camera instead of the F9000. Astrodon's Don told me of the residual image problems with the 9000 chip and if a new, faster scope were to be purchased in the future, 16803 is an all around better fit.

Which AO guiders do they use?

I've done a bit of reading on the AO guiding and this 6 months old thread is a bit discouraging: http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5454950/Main...


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550615 - 12/02/12 04:05 PM

Available AO units:

http://www.sxccd.com/sxv-ao-lf
http://www.sbig.com/Adaptive-Optics/

These AO uses transmissive glass instead of small mirror to save back focus.

SX AO is probably the best buy for high quality, great SX customer support and works with any autoguider and cameras.

SX user manual:

http://www.sxccd.com/handbooks/Starlight%20Xpress%20SXV%20AOL%20unit.pdf

Peter

Edited by Peter in Reno (12/02/12 04:10 PM)


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550620 - 12/02/12 04:15 PM

Same chip size, just smaller pixels. So no I don't. SBIG is working on one for it's 16803 cameras but don't think it works with other brands as their prior units use electronics in the camera for control, I'd expect that to be the case here as well. Might be another year before it is out. They say less but are notorious for not meeting projected availability dates.

I'd not heard much on the 9000 and its RBI problem. IR flooding can eliminate it but does reduce overall sensitivity from what I've heard.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5550632 - 12/02/12 04:22 PM

SBIG is out of question given it only works with their cameras so starlight express is the only one.

That thread mentioned that it's hard to find a suitable guide star for effective AO guiding, how that? I would imagine the narrow field of our f/10 scope doesn't help either.


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Peter in Reno
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Re: Guiding Schmidt–Cassegrain 300/3000 [Re: Migelo]
      #5550641 - 12/02/12 04:30 PM

If you have a sensitive autoguider camera like Lodestar, it will help find guide star. I use OAG with my C-8 EdgeHD at 2000mm focal length and I never had to hunt for a guide star thanks to high sensitivity Lodestar. I am not sure how well this will work at 3000mm focal length.

Imaging at 3000mm focal length will be very challenging unless you have a very good mount with smooth tracking like Astro-Physics, Paramount, ASA, etc. If you want to stick with your Meade fork mount, then AO may be the way to go.

One of the issue I see with AO is back focus. If you use a focal reducer which has a typical back focus of between 95 and 120mm, it's going to be difficult with AO, OAG, filter wheel and camera to meet this back focus.

You will need to do extensive research to meet your goal before purchasing expensive accessories.

Peter


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