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Old 05-05-2012, 07:19 PM
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CapturingTheNight (Greg)
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Focal plane shift?? Help please.

Hi all,
I am seriously tearing my hair out on this one. Set up the scope to take some quick shots of the moon tonight and for some unknown reason it seems like my focal plane has moved considerably. I have not used the scope for about two and a half weeks but nothing has changed or is different in my setup. I use a Bintel 10" F/4 imaging newtonian with the standard 2" crayford focuser. I attach a DSLR camera and multi purpose coma corrector. The focal point of the setup used to be well within the range of the focuser but now I can not acheive focus. It just starts to get focus when I run out of travel in the focuser (all the way out).
Is there anything that anyone can think off that might have happened since I last used the scope? The sledgehammer in the corner of the shed is starting to look tempting.
Cheers
Greg
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  #2  
Old 05-05-2012, 08:11 PM
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ballaratdragons (Ken)
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Sounds like you may have forgotten to add in an extension tube.

Did you ever use one?
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Old 05-05-2012, 08:16 PM
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tlgerdes (Trevor)
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Been here, done that.

Loosen your drawtube lock screw off another 2 turns, it is catching on the drawtube. It reduces the drawtube travel by about 7mm.

This is a known issue with the GSO focuser and caught me in my first week.
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Old 05-05-2012, 09:25 PM
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CapturingTheNight (Greg)
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Quote:
Originally Posted by ballaratdragons View Post
Sounds like you may have forgotten to add in an extension tube.

Did you ever use one?
Never needed one for direct imaging before Ken. I do need to add one if I want to do visual observation. All solved now though (I think) - see below

Quote:
Originally Posted by tlgerdes View Post
Been here, done that.

Loosen your drawtube lock screw off another 2 turns, it is catching on the drawtube. It reduces the drawtube travel by about 7mm.

This is a known issue with the GSO focuser and caught me in my first week.
Thank you for your thoughts Trevor, but I had already tried that. It was certainly not catching on anything. I think I just found the reason after calming down and having a think about it more. When I collimated the scope I must have pushed the primary mirror further up the tube than where it normally rests. I seated the whole primary right back down to the bottom of the tube, recollimated and bingo- the focal plane is now back to where it was. Phew! Thanks again guys.
Cheers
Greg
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Old 05-05-2012, 09:29 PM
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ballaratdragons (Ken)
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Excellent outcome Greg

Yeah, good point about collimating all 3 collimation screws by going forward only
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