Anonymous
Unregistered
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I'm having a major problem with the focuser on my Celestron 9.25 SCT and was wondering if anyone has run into this exact same problem before I pack my scope OTA up and ship it back.
Here's the problem: Whenever I get an object centered in the eyepiece (25mm eyepiece) and then go to focus, turning the focuser clockwise, the object jumps all the way to the right side and very edge of view of the eyepiece. I turn the focuser counter-clockwise and it comes back into view.
It gets worse.....When I try to use a more powerful eyepiece such as a 15mm or a 9 mm, the object completely disappears from view all together and I literally have to track the object down again by moving the scope and re-locating the object. This can't be normal!! 
I must add here that the direction of turning the focuser whether clockwise or counterclockwise doesn't have any effect on keeping the object in the eyepiece.
So, I am left with 2 options.... send the OTA back....or buy a JMI or some other focuser, although, I am not quite sure that this will correct the problem I have.
Any suggestions from all my knowledgable friends here at Cloudy Nights? 
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LivingNDixie
TSP Chowhound
Reged: 04/23/03
Posts: 17757
Loc: Trussville, AL
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http://www.jimsmobile.com/list_search.htm
I would go for the nonmotorized one myself, this would eliminate mirror shift all together... Hope this helps
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Preston
Meade 10in LX200R GPS UHTC
blog (updated 02/15/2013)
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Starman1
Vendor (EyepiecesEtc.com)
Reged: 06/24/03
Posts: 17639
Loc: Los Angeles
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Angel,
Sounds like you've contracted a major case of mirror flop (image shift). If this problem just developed (wasn't there when the scope was new), here are some possibilities:
1) focuser is loose. Check the screws that hold the focuser to the cell on the back of the scope. If they're tight,:
2) plastic ring that presses against primary mirror and presses it down onto the outer baffle sheath (that moves up and down on the inner baffle) has come loose. This can be checked by removing corrector plate (with secondary) and reaching into scope to try to hand tighten this ring. If it wasn't loose, then:
3) the pin that attaches to the baffle sheath under the mirror may have come loose. This is user serviceable if you are mechanically minded. You will have to remove the focuser from the scope and check for play in the pin to which the focus screw attaches. If it's wiggly, that's the culprit. You can tighten it by removing the corrector and the primary mirror from the scope, removing the movable baffle and tightening the focuser pin. If it's not loose, then:
4) the primary baffle may be cracked, allowing a lot of lateral movement in the outer baffle as it slides up and down on the inner baffle, or:
5) the entire baffle assembly with mirror has come loose from the back of the tube (the rear cell). This can be checked by removing the corrector and checking for lateral play in the baffle tube. Or:
6) The thick grease in between the two baffles has finally been scraped off the baffle interface. You can redistribute this grease by running your focuser from one end to the other 10 times or more and/or removing the focuser, then using a pencil + eraser against the back of the mirror to spin the primary mirror around several times to redistribute the thick interface grease, and reattaching the focuser.
All of these things can be checked by you if you are comfortable doing them. If not, a return to Celestron is in order. Because, though some image shift is undeniably a part of SCT construction dynamics, this amount is way outside the normal and does indicate a problem.
If you decide to do it yourself, I'd be willing to help you with steps on how to do it if you'd send me a private e-mail on this site.
Sorry to hear of your problem, but just be aware this is merely a fixable mechanical problem, and can be overcome (though you might be without the scope for a brief time).
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Don Pensack
www.EyepiecesEtc.com
12.5" Teeter/Zambuto, 5" Maksutov
Sustaining Lifetime IDA member
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Rusty
Postmaster
Reged: 08/06/03
Posts: 19246
Loc: Brooker, FL
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Yeah, I'd agree - a little flop with Celestron SCTs (or for that matter, the smaller Meades) is "normal", but not to the extent you've endured.
I think this is a candidate for return...
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N11GPS Fastar//TOA-130S//MK66 Std//AT6RC//Vintage C5//Megrez II 80mm APO//SolarMax 40
NJP Temma II//Sirius EQ-G
Too Many Astro-Cameras//Mallincam Color Hyper Plus
Two not-spoiled Golden Retrievers - Casey and Nelson
Lot 19 Deerlick Astronomy Village (Canis Major)
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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I forgot to mention that this was a problem from the first time I used my scope. I've had all kinds of problems with it since I first received it.
I got the scope in January from Astronomics but couldn't use it until February due to ice, snow and really bad weather. I used it once in February and never could get good views with it or get the motor drive to work properly.
The second time I got around to using it wasn't until June due to some health problems (now resolved  ) and it was the same as the first time. No good views, major focal shift, and couldn't get the go-to to work and align properly. (it was always 15 degrees off to the east)
The third time I went to set up my scope, two of the bottom cups on the tripod legs just fell off for absolutely no apparent reason. Obviously, I didn't get any observing done until I went out and bought some JB Weld and glue-welded the bottoms back onto the tri-pod legs.
By now, I am starting to think ..... "lemon" 
So, I take my scope with me to one of my Astronomy meetings with the St. Louis Astonomy Society and let them have a look at it. This was in June. They determined that it was out of collimation so that is why I wasn't getting "good views". It was cloudy out so we couldn't collimate. I tried to collimate the scope 3 times on my own but still noticed the focal problem and was still having go-to problems. By this time I am extremely aggravated.
2 weeks ago I take my scope to a Star Party at Carlyle Lake with the Astronomy Society and try to help me collimate it using an artificial star. Immediately 3 guys told my that there was something seriously wrong with my scope and to send it back. They said that the mirror had an astigmatism and that the focal shift was WAY off and shouldn't be like that. Well, I had already paid for another dark sky party for the following weekend, so.....
(this bring us to current date)
I went to the Springfield Dark Skies Party this past weekend and had 4-5 guys work with my scope and guess what...
it was a collimation issue, and they didn't see any astigmatism as everyone had seen before after the scope was collimated. (This was verified by all including myself by the crystal clear views I was now seeing!)  So I did a little happy dance and then jumped for joy when they were able to correct the go-to problem and get my scope running perfectly like it should have done "out of the box"!
Now, this leaves me with the problem of the focuser.....that was there from the beginning.
What a story eh? 
I am tempted to send it back to Celestron (I already have the shipping # from them) but we are now in PERFECT weather here and my scope is running and the views (when I can get them centered) are awesome.
I was hoping for an easy fix....but I am not sure if I can adequately take my scope apart and repair it myself as I would like to think that I can. I am mechanically and technically inclinded to do it, but I am also afraid that I may make matters worse.
Can a JMI focuser or something similar work for now? I can always send it back this winter. Perhaps? 
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Ken....
Pooh-Bah
Reged: 01/22/04
Posts: 1375
Loc: Nashua, NH, USA
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Angel, I just put a William Optics focuser on my 9.25 to solve the minor focuser shift I experience. Your shift sounds much worse, however, and not normal. Since your scope is still under warranty, I'd be leary in recommending you try to repair it yourself.
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Ken....
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Starman1
Vendor (EyepiecesEtc.com)
Reged: 06/24/03
Posts: 17639
Loc: Los Angeles
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Angel,
Image shift is a part of life for SCT users, but usually it's 1 to 4 arc-minutes at the worst. If it's a lot higher than that (and it sounds like it is), and the scope is essentially new, there is either an assembly problem (some examples I point out in my previous post) or a gross mismatch between the outer baffle and inner baffle. If it's an assembly problem, Celestron should make good on it. If it's a +/- tolerances issue between the baffle tubes, Celestron should make good on that, too.
Yes, you could add a Crayford focuser to the back, do gross focusing with the mirror focuser and fine focusing with the Crayford (which should have little or no image shift), but this is a way of mitigating what I think everyone would agree is a construction problem with your scope. Everyone with an SCT puts up with some image shift, but not to the degree that you experience.
Though it's hard to part with a new scope, I agree with the poster who said to send it back. When you get it back, it will still have the same fine optics, but not have the image shift magnitude. It is really not your problem--it is Celestron's.
And they will make good. I know several people who work there, and they do care about the quality of what they produce.
When you get it back, if image shift bothers you a lot, you may still end up adding the SCT Crayford focuser to the back, but at least the image shift will be tolerable for focusing at high power.
Through the years, I've seen a huge range of image shift in SCT's, but never so bad it literally took the object out of the field of view--even at very high powers.
Keep in mind the warranty period may expire, so you are better off sending it back sooner than later.
Wish I was there to take it apart for you, but if the problem ends up being a mismatch in the baffle tubes (which I suspect), I'd just end up sending it back, too.
Good luck!
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Don Pensack
www.EyepiecesEtc.com
12.5" Teeter/Zambuto, 5" Maksutov
Sustaining Lifetime IDA member
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BluewaterObserva
Postmaster
Reged: 05/18/04
Posts: 5748
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Buy the JMI focuser.. enjoy your scope. Not that it can't be made better, but those stock focusers will never hold a candle to the JMI products. Once you experience the difference, it will put a way big smile on your face.
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bierbelly
Postmaster
Reged: 01/23/04
Posts: 6179
Loc: Sterling, VA
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Quote:
So I did a little happy dance and then jumped for joy when they were able to correct the go-to problem and get my scope running perfectly like it should have done "out of the box"!
Angel, where have you been? Haven't heard much from you until just recently? Anyway, what did they do to fix your goto mount problems? I have the same problems, but no definitive fix as of yet.
Oh, BTW, at least one of the cups has fallen off of my tripod legs too. Guess they need some updated glue technology in China.
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12" DSH
8" f/4 Vega MakNewt
6" MN66
TV85
Edited by bierbelly (09/21/04 02:20 PM)
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Anonymous
Unregistered
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When you guys say buy the JMI focuser, which one are you talking about? Do you have the link? Are you talking motor focus?
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BluewaterObserva
Postmaster
Reged: 05/18/04
Posts: 5748
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Both the motorized and the manual versions, are way cool.
The NGF-miniC are the manual models for SCT's. The Motofocus for the SCT's can vary quite a bit by the size and exact model of the sct. The 8" version is the MFC8......
They are extremely impressive pieces, tested several times before they are released for shipping. (I'm biased some, even though I don't currently own any of their focusers, but I know and hang out with all those guys a fair amount) Including or maybe even especially Jim of Jim's Modile Inc.
You would be amazed at the QC they have on these products before they ever get to you.
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Anonymous
Unregistered
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I suppose you can bottom out with these focusers and hit the base of your fork mount
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Anonymous
Unregistered
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How bout this one? Its a lot prettier http://www.astronomics.com/main/William_Optics_2_rotatable_for_SCT_w_125_adapterWASCTF.asp/catalog_name/Astronomics/category_name/29WMUDQ0R33K9KPQCF8XVS44K4/product_id/WSCTF
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Rusty
Postmaster
Reged: 08/06/03
Posts: 19246
Loc: Brooker, FL
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I have that one - and use it for higher power viewing, but Angel's problems are one of mirror flop, and it's excessive for that scope....back it goes! 
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N11GPS Fastar//TOA-130S//MK66 Std//AT6RC//Vintage C5//Megrez II 80mm APO//SolarMax 40
NJP Temma II//Sirius EQ-G
Too Many Astro-Cameras//Mallincam Color Hyper Plus
Two not-spoiled Golden Retrievers - Casey and Nelson
Lot 19 Deerlick Astronomy Village (Canis Major)
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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michaeloconnell
Pooh-Bah
Reged: 08/18/03
Posts: 1065
Loc: Ireland
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I'd a similar problem on my scope.
It's mainly due to the way the focuser works as it tries to move the primary mirror from an off-center position.
I rang Meade and they said they would not accept a return unless the image shift was 2/3 the FOV in a 26mm eyepiece. Mine was more like 1/3 the FOV. As yours is a Celestron, try and return the scope. If you can't return it, here's what I did to mitigate the issue:
1) Turn the focuser clockwise until it reaches a hard stop ie. end of the focusing run. Now turn it anti-clockwise until it does the same. This helps to distribute the grease along the baffle tube. Do this 20 times. Do this before returning it and check your image shift. It'll probably be a bit better but not fixed. If it's still not correct, contact your dealer.
2) Part of what's causing the problem may also be backlash. I got the EZFocus kit and found it helped a little also.
3) You could get a zero-image shift focuser. For 1.25" eyepiecs I higly recommend the Borg helical non-rotating focuser and 1.25" adapter (parts 7315 & 7316). Although it needs the 1.25" adapter, this does not mean it's a 2" focuser. The focuser by default is threaded for SBIG camras and the 1.25" adapter is thus required to insert it in a diagonal. This fits between the diagonal and the eyepiece thus not creating an issue of clearance at the base.
Let us know how you get on.
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Michael
www.astroshot.com
...too many scopes, few clear skies....
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LivingNDixie
TSP Chowhound
Reged: 04/23/03
Posts: 17757
Loc: Trussville, AL
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Angel,
All SCTs have mirror shift the question is how bad is it. I haven't seen your scope so I can't say but alot of ppl upgrade to the focuser that I put in the link, yeah I know it was over $100 bucks. Try and fine someone who has an SCT near ya and do a comparassion and see how much shift the two scopes have. Also the earlier link I posted doesn't take you to the focuser. The focuser JMI makes is a NGF-C and its replaceing their NGF S and SE models
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Preston
Meade 10in LX200R GPS UHTC
blog (updated 02/15/2013)
Edited by LivingNDixie (09/22/04 01:29 PM)
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LivingNDixie
TSP Chowhound
Reged: 04/23/03
Posts: 17757
Loc: Trussville, AL
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Quote:
How bout this one? Its a lot prettier
I would get the JMI that I linked too, but thats just me...
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Preston
Meade 10in LX200R GPS UHTC
blog (updated 02/15/2013)
Edited by LivingNDixie (09/22/04 01:28 PM)
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Stelios
Pooh-Bah
Reged: 10/04/03
Posts: 1484
Loc: West Hills, CA
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Quote:
Can a JMI focuser or something similar work for now? I can always send it back this winter. Perhaps?
Absolutely it can. I have a JMI motofocus. It is pricey, but it's very good too. A few things about it you should know:
1) It will completely eliminate mirror shift. There will be zero vibration as well. It has a fast mode (for rough focus) -- just keep the button pressed and it accelerates -- and the (normal) very fine focus mode.
2) It comes with adapters that will allow you to operate it with both 1 1/4 and 2" diagonals, a nice plus.
3) It is built like a tank. You can drop it from the top of the Empire State Building and unless it lands on the buttons it will work fine.
Now the cautions:
4) The focuser only has about a bit over 1/2 an inch of travel. So you do need to "roughly" focus with your scope's focuser first. You may need to use the scope's focuser again if you insert a barlow or anything (bino-viewer?) that markedly changes where it focuses. However normal changing of eyepieces will be more than easily handled by the JMI.
5) You will need to build a holder for it (some velcro will do), else it will keep dropping (unharmed -- remember like a tank -- but annoying) as you GoTo another destination and the scope stretches the cable.
Overall it's simply great.
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APM/TMB 115/805 APO
9.25S - GT
Naglers: 17T4, 13T6, 3-6 zoom
UWANs: 28mm, 7mm
Pentax 10XW, 10mm Radian
Misc EP: 50mm Parks, 42mm GSO, 2x TV Barlow
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michaeloconnell
Pooh-Bah
Reged: 08/18/03
Posts: 1065
Loc: Ireland
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Can a Williams Optics SCT diagonal fit onto the JMI NGF-C?
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Michael
www.astroshot.com
...too many scopes, few clear skies....
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Bluemeanie
scholastic sledgehammer
Reged: 01/26/04
Posts: 903
Loc: Scranton, PA U.S.A.
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Quote:
Can a Williams Optics SCT diagonal fit onto the JMI NGF-C?
YES! I comes with an adapter so all of your SCT threaded stuff can go into the focuser. I have a JMI-C and love it!
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Walt
- Obsession 15" f/4.5 #1282 w/ Argo Navis, Feathertouch Focuser
- Meade 2080GEM (8" SCT)
- Vixen ED80SF - Celestron CG5-GT Mount
- Coulter CT-100 - Meade DS2000 Mount
- Coronado Halpha PST
- Denkmeier Binoviewer w/ dual PXS
- Canon 300D, Celestron Neximage
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