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Migelo
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Guiding Schmidt–Cassegrain 300/3000
      #5526197 - 11/18/12 01:55 PM

Hi!

What kind of guiding would be the best for a Schmidt–Cassegrain 300/3000 telescope?

OAG or a separate guiding telescope?


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5526483 - 11/18/12 05:02 PM

OAG with any moving mirror scope. Mirror locks rarely do the job. I had to modify mine beyond recognition so it no longer can be focused that way. Took help from a friend with a machine shop and several months of work. Still, when I guide I use the guider chip in the STL-1100XM.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5534055 - 11/22/12 02:37 PM

So this would be cool for a KAF 9000 sensor?

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p4353_O...


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5534099 - 11/22/12 03:33 PM

That chip is 52mm diagnonal while the OAG you link to is good only to 42mm diagnonal as I read the page. It would work with a 11K or smaller chip but not those larger than that.

A couple other considerations. Can you even use a 52mm diagonal? My 14" (356mm) LX200R only supports about a 42mm diagonal chip due to its 45mm baffle tube well in front of the CCE. Larger would vignette corners more than I'd want to flat field out due to the high noise that would create in the corners. I doubt any 300mm SCT can support that chip. The 12 micron pixel is a good match however to that focal length at 0.8" per pixel. Might make up for the need to crop out part of the chip.

Meade now has out a line of SCT's (LX600) using an internal Crayford type system to move the main mirror. They claim it does fully lock the mirror from moving. I have not heard if it works as advertised. If you have one of those then you might try the separate guide scope method and see if it works. Keep in mind flex in such a system at that focal length is very difficult to control. Takes a super focuser on the guide camera even with a very light camera and/or a separate support for the camera along with very solid mounting of the guide scope. Only threaded mounting of the imaging camera will be sufficient as well.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5535105 - 11/23/12 09:28 AM Attachment (22 downloads)

Thx, seems I'll have to look out for another OAG. =)

The telescope is LX200 and I calculated that with the baffle tube radius of 22,5mm we'd waste about 4,9% of the chip. See the attached picture, full calculations are here but to understand the calculations, you should check out the attachment: Calculations

How much more would go to waste due to vignetting at the corners.

EDIT: Corrected the result.

Edited by Migelo (11/24/12 05:07 PM)


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5535604 - 11/23/12 02:15 PM

Vignetting starts at the very center of the image and increases at an ever increasing rate toward the edge suddenly getting greater at some point less than the diameter of the baffles. How far those are from the objective and the f ratio of the system has to be taken into account too in any math model. Other bottlenecks need be included.

22.5mm for the baffle radius is the same as in my 14". The corners of my 11K chip are about 42mm diagonally. I get a drop off of about one magnitude at the corners due to vignetting. If the night gives 23rd magnitude in the center it will drop to 22 at the corners, maybe a bit more. Flat fielding hides this but if you look closely you'll see the increase in signal to noise ratio. Where this becomes objectionable is a very personal thing. No hard and fast rule on how much is too much. Some might find this too much but I've rarely found it important.

Assuming that you feel the same then your scope too would handle a 42mm square out of the 52mm square which would waste about 35% of the chip (1-42^2.52^2).

You have to weight the added cost of wasted silicon of that chip over say the 11K vs the somewhat longer sub exposure time needed with the 11K's smaller pixel size to reach sky limited exposures. Once sky limited then the total exposure time is the same for the same image scale achieved after the fact with software binning. Or maybe you have another use for the chip that doesn't waste the silicon.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5535667 - 11/23/12 02:48 PM

But I could've just cut the image at the corners and get smth like the paper used in Battlestar Galactica, albeit the cut would be more noticable:


If I did that, I wouldn't lose so much of the chip.


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5535928 - 11/23/12 05:39 PM

And are you sure about that information on the baffle tube?

I got this:

12" LX200:

Main baffle tube OD is 2 1/2"
Main baffle tube ID is 2 3/8"
Secondary baffle length from inner surface of the corrector is 1 -21/32"
Secondary baffle OD is a shade under 4" say 3 -63/64"


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5535968 - 11/23/12 06:05 PM

I can only speak to what I measured in my early 14" LX200R when I had it apart. The tightest bottleneck was about 42mm.

If this is just the LX200 model you will need a field flattener. Those usually reduce which would further restrict the usable field of view.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5535980 - 11/23/12 06:14 PM

This sucks! We'd be wasting a lot of that expensive chip.

This is a 12" telescope. I'll look more in this matter.


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5536543 - 11/24/12 01:12 AM

35% would be below my standards, yours may vary but your method of calculation is far too arbitrary. Vignetting varies across the field. Even 100 pixels from center it will start to drop off as that part of the chip sees the aperture slightly oval and thus smaller in area. With my LX200R the drop is about 1 magnitude at 42mm diameter circle which is invisible to the eye once flat fielded. Beyond that the eye starts to see a drop in signal to noise ratio that I find too much. Others may find that point inside or outside that circle. To get that I use a 3" focuser (my mirror is truly locked making an external one necessary) and all connections up to the camera are that size. When I use a 2" vignetting was worse. I quickly upgraded to 3". Well 3.1" to be more exact. Now the vignetting is solely inside the OTA.

Virtually all my posts here (labeled full image) use the full 42mm diagonal of the chip. Only by measuring noise in the corners or by checking limiting magnitude there do you see the vignetting after proper flat fielding. Beyond that however things go bad quickly, hence my choosing the 11K to best cover the usable field at reasonable resolution (1" at 2x2 and 0.5" at 1x1 when conditions permit -- not very common unfortunately).

Besides vignetting you have field curvature to deal with unless that is a newer model with ACF optics. Otherwise a flattener/reducer would call for a smaller chip with smaller pixels for the same resolution and true field of view. Even with those optics I have noticeable curvature in the corners so doubt it could support anything larger even without the vignetting.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5537415 - 11/24/12 03:43 PM

Well, my calculations included only the part of the chip that would get no light at all.

So, today we went to that telescope in the observatory and checked it out.

The last part that is attached to the telescope is:



It's attached to this:

Had to make it in SketchUp, all pictures were blurry as hell!

And as you said, the diameter is 45mm:


So, if we could make/buy that part just with 52mm instead of 45mm, would it be ok?

This is a newer version with ACF optics.

Thanks for helping me out.


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5537776 - 11/24/12 08:12 PM

That would be about the inside diameter of the 2" focuser that added to my vignetting. I no longer have it so can't measure it. Obviously won't fit the 9000 chip size, even 52mm would be pushing it for that chip.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5539256 - 11/25/12 06:56 PM

If we can somehow make 52mm work, we'll take it, but it seems messy.

Which camera would you suggest? With your 11k, how many times is it usable?

And to get back to the original subject, do you know of any OAG that works well and would fit this CCD or any of those you suggest.


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5539455 - 11/25/12 09:37 PM

MegaMOAG is usually the choice with large chips. http://www.astrodon.com/products/hardware/megamoag_off-axis_guider/

I use the 11K every clear night for something. Haven't been many of late, snowing right now.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5540358 - 11/26/12 01:56 PM

That thing costs 1400€ in EU.... xD

I got a reply from Meade about what we're talking about:
Quote:

Dear Mr. xxxxxx,

if you use the biggest possible rear cell thread (should be 3,25" for the 12" with a step down ring to 2") it should work. Only setback will be the inner diameter of the main mirror baffle tube, which is 2 3/8" for the 12" LX200.
Actually 53mm is quite big so we have no real experience or test photos.


kind regards,
xxxx xxxxxxx




So this means the narrowest part is 60.33 mm wide. That should be enough for the chip with a diagonal of 53mm. The part I don't get is:

Quote:

(should be 3,25" for the 12" with a step down ring to 2")



Does that mean that the narrowest part is actually 2" wide? I'm confused what a "step down ring" does or looks and what is it's purpose.


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5540503 - 11/26/12 03:20 PM

I think they mean to keep everything at 3.25" until you reach the camera. I'm at 3.1" with the 11K all the way to the camera. When I stepped down to 2" before the camera I had considerably more vignetting from the light cone as well as reflections off the walls of the 2" focuser tube. Keeping things wide prevents anything hitting something and reflecting into the camera. I still can get a reflection from the mounting hole for the 2" filters which can be a pain. As I mentioned before vignetting is only part of the problem!

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5540538 - 11/26/12 03:37 PM

Ok thx.

So the configuration for this large CCD would be:

-LX200(12")
-3.25" rear cell thread
-monster OAG (or any other large OAG)
-FLI CFW-5-7 Filter Wheel
-FLI PDF (or any other large focuser)
-PL09000 camera

This should be fine, if I'm not mistaken.
How can I calculate if I'm going to run out of backfocus? I just want to be sure, even thought I know that SCT have the most focus of all.


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Rick J
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5541415 - 11/27/12 12:50 AM

Unless you are using 3" filters they shouldn't come before the focuser. Also putting the focuser after the OAG means as you need to refocus the camera you'll need to refocus the guider as well.

Put the focuser first, then the mega MOAG then the filterwheel then camera.

Unless your main mirror is totally locked like mine why not use the normal focuser. I know several using focusmax with a RoboFocus unit on the moving mirror focuser with OAG and getting excellent results. It approaches focus from only one direction so backlash isn't an issue and the OAG compensates for all mirror slop.

I went my route simply because I don't guide at all unless imaging outside of the area of my TPoint map. That made the totally rigid mirror a necessity. If I were guiding I'd have not locked the mirror and let the far cheaper RoboFocus unit alone handle focusing.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5542340 - 11/27/12 03:30 PM

Thanks for the positioning tip! Our filters are square 50mm so thanks again.

I just found out that FLI PDF is not made to work with OAG. (fli support told me that).

So you say RoboFocus will do a good job? (we're not going to have a totaly locked mirror on the SCT)


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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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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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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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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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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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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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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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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 new [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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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5550652 - 12/02/12 04:44 PM

We're not going to use any focal reducer, because it would cause huge vignetting, so backfocus won't be a problem.

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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550666 - 12/02/12 04:54 PM

Maybe go in baby steps. Start autoguiding only with OAG and go from there. Make sure the OAG will work well with AO in the future so you won't have to buy a different OAG just to work with AO. If you are satisfied with this results then you are set. Otherwise AO may be the next step.

I also suggest to get the highest sensitivity autoguider camera if you choose to use OAG. Lodestar may be the best. SBIG also has a pretty high sensitivity autoguider camera called STi but it uses a noisier Kodak CCD and you may see more hot pixels than Lodestar but hot pixels may be removed with dark subtraction.

Peter


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5550675 - 12/02/12 05:02 PM

That's a nice idea.

So I'll take that OAG-6 OAG and this lodestar camera for guiding: http://www.teleskop-express.de/shop/product_info.php/info/p2915_Starlight-Xpr...

and see how it goes. If needed, I may purchase an additional AO unit.

Does that moving prism in the OAG-6 do bad stuff if used with AO?


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550688 - 12/02/12 05:10 PM

I am not sure what you mean by moving OAG's prism doing bad stuff to AO. I am not familiar with AO, I only mentioned SX AO from reading reports. Once you moved the prism to the desired spot, you can lock it and it will never move. Just don't let the prism go too far down that could obstruct part of the CCD camera. The lower the prism the better so that it's closer to on-axis and the stars would be rounder. Stars at off axis tend to be elongated.

Peter


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5550714 - 12/02/12 05:25 PM

I was just wondering if in the case that the prism is not parallel with the AO moving parts, it could lead to some errors, just wanted to cover all the bases. xD

And noted the prism-not-obstructing-CCD-camera part.


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5550726 - 12/02/12 05:32 PM

From what I have read, Maxim should take care of the mechanical imperfections (parts not parallel with each other) by running a calibration. SX software for AO does not have calibration so the autoguider must be squared with AO. I don't think you have to worry about this with Maxim. I would consult with Maxim and SX about this.

Peter


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5550802 - 12/02/12 06:29 PM

The guide camera in that thread is not very sensitive. Works with a separate guide scope but can be a big hassle otherwise. With a decent guide camera, like the LodeStar and 12" aperture you won't have an issue for guiding. Finding one for correcting seeing which takes =<0.1" is often a problem however. This is where The Sky I think you mentioned as having will help as it can show you the ring your guider can reach around your chip. This makes it very easy, especially if you have a rotator.

While I don't guide very often the guide chip in my camera is even smaller than a LodeStar into that prism and I've never had an issue finding a guide star even working behind the filters and you are working ahead of the filters.

The SBIG AO unit is for much smaller chips. At 60mm the other one is marginal. Contact them to be sure it will work. Your chip is 52mm corner to corner and while its clear aperture is 60mm you need considerably more to give room for guiding. How far you can go before bumping the mount with it I don't know. Likely not very far. Since you are permanent you can get very good polar alignment so if it can handle the periodic error that should be sufficient.

Rick


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Migelo
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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Rick J]
      #5551774 - 12/03/12 10:16 AM

As it seems, I'll be going with the StarlightXpress AO unit, because it's about the same price as MonsterOAG and OAG-6, here in Europe.

It's an OAG with AO, so I'll be getting 2 for the price of 1.

What is your opinion?

@Rick: What do you mean by "The Sky I mentioned"


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5551806 - 12/03/12 10:46 AM

I think you should double check whether OAG comes with SX-AO. I believe SX-AO and OAG are sold separatly.

Peter


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5551814 - 12/03/12 10:52 AM

It does come, it says so on the site and I've just used Skype credit to call StarlightXpress and they also confirmed it.


http://www.teleskop-express.de/shop/product_info.php/info/p2922_Starlight-Xpr...

It says, right to the picture: Off Axis Guider included

StarlightXpress said that the prism will cause some obstruction if streched all the way, because the AO unit was intended to be used with the 11000 chip.


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Migelo]
      #5551837 - 12/03/12 11:03 AM

That's good to know. The picture showed a thicker OAG. SX also has Ultraslim OAG to allow to include filter wheel. Adding filter wheel to the thicker OAG may cause parfocal issue between main and guider camera. See picture of SX-AO with Ultraslim OAG and filter wheel at:

http://www.sxccd.com/sxv-ao-lf

I wonder which OAG comes with SX-AO. You might want to contact the vendor and ask if it can come with Ultraslim OAG.

Peter


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Re: Guiding Schmidt–Cassegrain 300/3000 new [Re: Peter in Reno]
      #5551861 - 12/03/12 11:17 AM

Did just that and they said the slim version of their OAG is to be used with their filter wheel.

The AO unit comes with their standard "thick" OAG.


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