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drexelpbp
member
Reged: 01/21/08
Posts: 37
Loc: Phoenixville,PA
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Hi
I just purchased a Celestron C8 on Astromart. Its the Carbon Fiber model. It arrived about a week ago. It appears to be in excellent condition - like new.
Last night was the first night I was able to use it. I found two significant problems:
(1) I could not get it to come anywhere near focus
(2) While attempting to focus the image moved all over the place.
Given that I am a complete neophyte with this type of scope I was hoping that someone could give me some advice and point me in the right direction.
Thanks for any help you may be able to provide.
Gary 
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werewolf6977
Lord High Smasher
Reged: 12/15/03
Posts: 7401
Loc: Hanover, Ohio
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Do you have a star diagonal? They add length to the optical train. About the image moving, that's called mirror flop. What ep were you using? MIrror flop is more noticeable at higher magnification. At least that was so with my N8.
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Pete
6" Apogee/LXD55 - "The Beast"
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garyc11
Carpal Tunnel
Reged: 11/20/04
Posts: 2777
Loc: Niagara Falls,NY
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first thing i would do is check the collimation
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CGE 1400
CPC 1100
MallinCam Hyper Plus Color
Celestron 100 ED
CG5-GT
Celestron C-8 Newtonion
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 6494
Loc: Mandeville, LA USA 30.38 X 90....
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What you are seeing while focusing is actually called image shift. It's inherent in most SCs due to the configuration of the focuser relative to the mirror.
Mirror flop happens when you slew the scope from one side of the meridian to the other. Gravity will shift the primary mirror.
One thing that you might want to do while focusing is get the scope lined up on a bright star like Vega. Then focus very slowly. I've read more than once that the only problem was observers were actually focusing too fast and going right past the focus point.
An SC has a lot of focus travel. It should focus, diagonal or not. Also, use a low powered eyepiece.
David
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A few scopes and mounts.
Proud Member; PAS NOLA,
Life expectancies would go WAY up if green vegetables smelled like bacon...
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sang33ta
professor emeritus
Reged: 07/08/08
Posts: 539
Loc: UK
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DON'T PANIC!
Try focusing in your widest eyepiece (highest number). Some days when the air is bad you can't get focus, this is normal. I recommend a 40mm or 32mm for initial focus.
The moving image may just be your mount locks are not tight or your tripod/mount is too weak for your scopes weight.
Of course if it's wobbling it's gona be mighty hard to focus so these two problems go hand in hand!
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Hioptic 152mm f12.5 Maksutov
Celestron Advanced CG5-GT Mount (Mr Noisy!)
Meade 4000 Super Plossl Set
Casio QV-2900UX
Got fed up of waiting for Meade ETX-150 so put this together for £500/$1000 
Edited by sang33ta (07/26/08 11:03 PM)
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drexelpbp
member
Reged: 01/21/08
Posts: 37
Loc: Phoenixville,PA
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Thanks for your response Pete.
I was using an astro tech 1.25" mirror diagonal and a Baader Hyperion EP. Do you think I should try a different diagonal?
Thanks
Gary
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sang33ta
professor emeritus
Reged: 07/08/08
Posts: 539
Loc: UK
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Try focusing on a land object during the daytime it will be easier. How many mm is your eyepiece?
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Hioptic 152mm f12.5 Maksutov
Celestron Advanced CG5-GT Mount (Mr Noisy!)
Meade 4000 Super Plossl Set
Casio QV-2900UX
Got fed up of waiting for Meade ETX-150 so put this together for £500/$1000
Edited by sang33ta (07/26/08 11:43 PM)
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