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MichaelW
Pooh-Bah
Reged: 06/03/06
Posts: 1398
Loc: Cartoon City, Nirvana
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So is the Moonlight zero image shift focusers a good choice? Is there a different one you would recommend? I will be adding a motor focusing to it.
Do you need something special for mirror locking?
I will be using the SCT for imaging primarily. If I lock the mirror in a position is there enough travel for prime focus and barlow use with an imager camera. And if I through regular viewing into the mix does this change things?
Thanks for fielding my newbie questions.
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Michael W
Backyard Astronomer @ Washoe Zephyr: 
Arizona Sky Village: 
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 11083
Loc: Los Angeles
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I presume, from your post, that your SCT does not already have a mirror lock or a microfocuser.
You should determine the focal position of the rear-mount focuser by first adjusting the mirror focuser on the scope's rear cell. Then, microfocusing can be accomplished with the external focuser.
JMI, MoonLite, William Optics, Clement, Van Slyke, and others offer this external focuser.
It may prove necessary to add an under-the-tube counterweight system to balance the scope with this much rear-mounted weight.
As for locking the mirror once you've found the proper position, the solution is not easy. It entails the addition of a threaded screw on the rear cell of the scope that can press against the mirror to hold it in place. The installation of said screw usually requires a complete dismantling of the tube, an easy task if you know what you're doing, but not a job for the faint-hearted or mechanically inept.
What I suggest is to not install a mirror lock, and stop your exposure before the telescope crosses the meridian. Resume shooting once the scope has passed the meridian and the mirror has "flopped" (or, shoot through the meridian and discard that shot when stacking).
The advantage of not locking the mirror is that coarse focus can still be achieved with the rear cell focus knob, and fine focus with the external focuser. You WILL need a focus lock on the external focuser, though, as they tend to slip from the weight of a camera, etc.
One last note: there is no such thing as a too-heavy wedge. If you can, get a better wedge than the standard Meade or Celestron wedge, like a Milburn or even heavier. Your photography will be a lot easier, and gentle breezes won't make you fearful of having to start over.
Best of luck to you.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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Rusty
Postmaster
Reged: 08/06/03
Posts: 16512
Loc: Brooker, FL
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You didn't say which SCT you have, but the Meade 12" and 14" have mirror lock provisions and the new ones come with a microfocuser. Others' mirror locks would have to be user-installed (NOT a task for the faint-hearted). Mirror flop isn't a very big issue unless your image duration takes the scope past the meridian.
However, with mirror lock, the technique is to rough focus with the stock focuser with the outboard focuser in the center of its range, lock the mirror, then fine focus with the outboard, so any outboard focuser will have enough range.
You may find that a motorized focuser is easier to use (no finger-induced vibrations, and you can focus while watching the laptop screen). However, as good as the Moonlight focusers are, you may find the extra $140 for motorizing one is outside budget constraints. A reasonably good substitute would be the JMI NGF series...
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N11GPS Fastar
TOA-130S
MK66 Std
Vintage C5
Megrez II 80mm ED Triplet APO
SolarMax 40
NJP Temma II
Sirius EQ-G
ST8XE/CFW-8(LRGBHa)/AO-7/DF-2/STV Dlx/ST237a/350D (Unmodded)/Mallincam Color Hyper Plus/DSI III Color/DSI II Pro
Two not-spoiled Golden Retrievers - Maggie and Casey
Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering. - Arthur C. Clarke
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MichaelW
Pooh-Bah
Reged: 06/03/06
Posts: 1398
Loc: Cartoon City, Nirvana
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Thanks! Good information that I did not know as I have never owned and SCT before. I am looking at the Celestron 9.25 or 11 but leaning heavy to the 9.25 as my camera weighs so much. So is it safe to assume that a new C9.25 would have a mirror lock? So the zero image shift focuser doesn't replace the factory focuser but works in conjunction with the factory focuser. Hmm, cool. I never knew that. I'll have to look into the bevels and counter weights. Thanks again.
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Michael W
Backyard Astronomer @ Washoe Zephyr:
Arizona Sky Village:
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JerryWise
Postmaster
Reged: 12/26/03
Posts: 7006
Loc: Lexington, SC
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Quote:
..............So is it safe to assume that a new C9.25 would have a mirror lock? ............
I've had a number of Celestron OTAs/scopes including a new C-11 and none have mirror lock. The Celestrons have a well machined mirror support assembly. The mirror lock is a nice feature but for me it isn't necessary. I don't use the one on the Meade LX200Rs either. Just rough focus with the mirror focuser then fine focus with the FeatherTouch works fine. (Or fine enough for my skills.) 
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Jerry
LX200ACF 14", Tak FS 152 & TOA 150
AP-1200 & Mach1
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astroborg
member
Reged: 02/04/04
Posts: 46
Loc: DC Suburbs, VA, USA
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Jerry:
I just got a Feathertouch for my Brandon 94 refractor. I see you and I both have C9.25's - are you happy with the Feathertouch on your SCT?
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-Rich
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Rusty
Postmaster
Reged: 08/06/03
Posts: 16512
Loc: Brooker, FL
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Quote:
Thanks! Good information that I did not know as I have never owned and SCT before. I am looking at the Celestron 9.25 or 11 but leaning heavy to the 9.25 as my camera weighs so much. So is it safe to assume that a new C9.25 would have a mirror lock? So the zero image shift focuser doesn't replace the factory focuser but works in conjunction with the factory focuser. Hmm, cool. I never knew that. I'll have to look into the bevels and counter weights. Thanks again.
The difference in weight between the C11 and the 9.25 is only a few pounds, so I'd suggest the larger ensemble.
A counterweight rail and counterweights would have to be considered essential if you're hanging a heavy camera on the rig, and the 9.25" has no advantage over the 11" in that regard. Actually, I'd consider them essential for all viewing or imaging.
The 11" is, well, 11" - and the 9.25 is a bit smaller.
Now you also have to consider your camera and the focal length of the scope. a NexStar or CPC scope (both alt-az mounts), you'll need a wedge to prevent field rotation.
So, if the scope is still on your wish-list, I'd recommend favoring the Celestron CGE or the Orion-marketed Atlas EQ-G 11"; the former is considerably more expensive, but is a mount even more robust than the Atlas. Both are equatorial mounts, and better-suited for astrophotography, and the CGE is much better than the Atlas.
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N11GPS Fastar
TOA-130S
MK66 Std
Vintage C5
Megrez II 80mm ED Triplet APO
SolarMax 40
NJP Temma II
Sirius EQ-G
ST8XE/CFW-8(LRGBHa)/AO-7/DF-2/STV Dlx/ST237a/350D (Unmodded)/Mallincam Color Hyper Plus/DSI III Color/DSI II Pro
Two not-spoiled Golden Retrievers - Maggie and Casey
Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering. - Arthur C. Clarke
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Anonymous
Unregistered
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All the previous advice is great, I'll add one more thing - robofocus. If you're primarily into imaging then it is just about indispensable, IMHO. Critical focus is one of the most important steps to good imaging at SCT focal lengths, and with Robofocus and appropriate software you'll get critical focus every time.
Robofocus is a stepper motor unit with control box & software that interfaces with just about any focuser (SCT focuser, R&P, Crayford, Clement, etc...) and allows for computerized critical focus, as well as automated focus. I personally use Focusmax for this, which is free.
My setup is a Van Slyke Crayford outboard focuser, a locking SCT focus knob from Hutec ($40, easy install, works quite well), and Robofocus. I wouldn't have it any other way for imaging.
cheers,
john t.
http://www.lunacie.com/re.aster
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conus
Carpal Tunnel
Reged: 10/12/03
Posts: 2978
Loc: OC, Calif
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Quote:
The advantage of not locking the mirror is that coarse focus can still be achieved with the rear cell focus knob, and fine focus with the external focuser.
This is the problem I ran into. I sold my C9.25 last year and was just about to replace it with another that I could use, not only for the planetary imaging I'd already been doing, but also to get my feet wet with longer exposure stuff. My plan was to have the OTA shipped to Woden Optics for flocking and to have the mirror locked down, when I realized I wouldn't be able to do both kinds of imaging. The focal point positions would be so different, particularly since I wanted to use another Feathertouch, that moving the primary would be necessary when switching back and forth. I've just about decided against any compromises, but the alternative is going to be expensive. It's going to mean two telescopes.
I definitely want another C9.25 for lunar and planetary stuff. It's big enough to resolve the sort of detail I want, without being so seeing dependant that I'm limited to fewer nights of imaging. For DSOs I'm pretty sure I'm going with Vixen's 8" f/9 VC200l-- a sort of classical Cassegrain with a flattener added to the primary's baffle tube. It sells for around $1700.00 and provides wide, flat fields of view. The mirror is locked! There's no corrector plate, no image shift, includes a flip mirror and weighs only 13.2 pounds. Vixen makes a reducer for it and every aspect of this scope is collimatable. I've seen images taken with it that looked like they were made with Ritchey-Chrétiens of similar aperture.
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Steve R.
12" Orion XTi
Fujinon 10x42
Oberwerk 12x60
My toUcam Images
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