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Old 16-02-2009, 09:57 AM
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Omaroo (Chris Malikoff)
Let there be night...

Omaroo is offline
Join Date: Aug 2006
Location: Sydney/Cooma
Posts: 7,628
Hi Daniel

Are you reaching focus and having trouble making it precise, or are you lacking in travel such that you'd never reach focus to begin with? Given that you have a Newtonian, maybe your focuser assembly is too long and you need more in-focus travel that you've got. The only way to fix this (if it is indeed the problem) is to either swap the focuser assembly for a low-profile (read: shorter) focuser or physically relocate your primary mirror up the OTA towards the secondary a bit.

Well, a camera is just another device at the end of the optics train that tries to do the best it can with the light received - whether it's in focus or not. A camera isn't unlike the eye - you still need to focus it to see a clear image.

Do a search here on IIS for the "Bahtinov Mask". It's a simple device that you temporarily place on the end of your scope that, when pointed to a bright star, will show whether you are at focus or not by taking fast 1-second images and looking at them on-screen. As you move focus in either direction you will see the shape of the six-spiked diffused star change, and when everything is symmetrical you have reached focus. It's the fastest and easiest way in my opinion to get as close as you can to proper focus.
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