Quote:
Originally Posted by RobF
More temp shift with some designs than others Ben. If your ED80 has metal tube then you'll need to focus more frequently during times of the night temp is changing the most.
With my refractor the need to focus can reduce a lot if the temp stabilises through the night. Depending on length of your subs and temp fluctuations you might want to vary between focus on filter and focus on time options in SGP. All the better if you have a reliable temp readout to trigger refocusing.
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I looked up local temp forecasts and the temperature variation was pretty minimal last night (a degree at most). Can’t imagine the temp would be vastly different in my backyard a few kms away from the weather station? Wonder whether the shift in focus had more to do some kind of backlash in the system caused everytime autofocus runs? The weight of the camera and filter wheel might have put some strain on it all although V curves were consistent. The difference was always 250-300 inwards although I reverse the auto focus direction in SGP for my refractor. Not sure what this means for the focuser position readings. If IN is in fact IN then backlash on the gears and/or motors would make sense as the focuser would find it more difficult to drag the imaging train in (after heading out first for the autofocus run) resulting in an estimated focuser position that seems further IN (focus actually is in the same position but the motor think it’s futher in). I had a nominal 10 steps for backlash. Might up that to 250! It’s a single speed Skywatcher focuser so that might also have an impact.