Old 28-01-2013, 11:37 AM
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Location: southern highlands, Australia
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Achieving focus on a 12'' dob

Hi everyone,

Lately I have gained interest into astrophotography mainly from my recently purchased Canon 550 D.

I have taken some shots on a still tripod and stacked them with some pleasing results although an eq mount would ofcourse be better, though being a student its an expensive realm.

So I bought a t-mount and 2'' adapter. Attached it to the camera and slid it into the focusser only to get a a big blurry image of the moon. I tried focusing outwards and the image became more blurry. Focused inwards and the tube would not go any further in.

I have heard that, moving the mirror up would solve this problem. though I really don't want to be hacking away at the tube.

So if there is any other means of being able to achieve focus,please let me know.

thanks in advance, Orestis
PS- would a 1.25 '' adapter cause vignetting , because I have a small 5'' reflector I could try it on.
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Old 31-01-2013, 08:14 AM
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Shiraz (Ray)
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Location: ardrossan south australia
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you might try a 2x 2 inch Barlow, which should get to focus without moving the mirror (1.25 is too small). will give you additional magnification, but that should be OK on the moon and planets. Barlow will also help with your "bunch of Plossls" - they will work a bit better with a reduced light cone angle (higher magnification though). I have one of the GSO 2 inch Barlows - something like that should be suitable. If you know anyone with a Barlow, try it out before purchase just to be sure that it will work with your scope geometry and focuser design - and that everything fits.

Last edited by Shiraz; 31-01-2013 at 07:50 PM.
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