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Originally Posted by avandonk
Eric the only way to get perfect focus is by test exposures. The problem then is if the temperature changes or the scope or lens is still cooling down you lose perfect focus. I have been battling with this from day one. That is why I built the stepper focuser. This allows me to calibrate the lens or telescope for true focus position as a function of temperature. It is a lot of trouble initially but saves a lot of time in the long run. I found that by the time you notice focus going 'off' during a series of sequential exposures and then get dark adapted and refocus anything up to an hour is lost.
This is what makes astrophotography 'fun' so many variables you have to try to control. Everybody has their own 'methods' of coping.
I am afraid there is no simple or correct answer.
Bert
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Cheers Bert. thanks for the idea. Any pics of your stepper focuser?