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Old 09-05-2013, 02:13 PM
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PRejto (Peter)
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PRejto is offline
Join Date: Jan 2011
Location: Sydney, Australia
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Originally Posted by Terry B View Post
I don't have an ONAG but the process of focussing the guide camera should be similar to my spectrograph. Once it is par focussed with the camera you should not have to touch it again.
I just aimed at a really bright star with a bahtinov mask. Focus the main camera using a subframe and a very short exposure so that you have almost real time updating on the screen. Once you are happy with it then lock down the focusser. You then move the guide camera manually in its holder watching the screen in real time. With my STi I use a 0.1 sec exposure and this will still show the diffraction spikes from the mask. Once it is focussed, lock the position tightly. You should not need to touch it again as you just need to focus the main camera for each target.
Hi Terry, You are correct. Once the guide scope is focused you don't need to change it. I'm just not very fond of the focusing options built into the ONAG. It consists of a short tube held in a clamp that can be loosened or tightened down...there is no other way to focus other than sliding the tube in or out. The only way I could fine focus was to rotate the camera on the camera threads. Not ideal, but it works. Next time I do it I will try a mask as you suggest, but due to the distorted star shape coming through the mirror I'm not sure how the mask will look. Many thanks!
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