Quote:
Originally Posted by Shiraz
sure is a problem Stuart - a real pain. In the region of f4, there is next to no tolerance. CF helps, but as you point out, the Al stuff does it's own thing anyway and you still need to refocus at the slightest temp change.
FWIW, I need to refocus at about every 0.2 degrees with my current steel tube f4 - I have just bought a CF scope, but back of the envelope calcs show that I will still need to refocus about every 0.5 degrees.
Do ASA provide any temp sensing for their focuser? - would have thought that it should be relatively straightforward to get a high end focuser like that to track with changing temps, which is what you will need if the focus is drifting within subs. If they don't, there are a few stepper focuser drive systems out there that incorporate temp sensors - doubt there is anything magic about ASA stepper motors, so it should be fairly straightforward to use an alternative interface box and get one that can operate with your chosen software.
The other thing that is useful is a low read noise camera, which allows short subs - only a consideration if you are in the market for a camera though.
Could an aircon in the obs be an approach to get your system ready for imaging before midnight?
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Hi Ray,
Thanks for the input.
I do believe that the ASA has temperature compensation built in, looks like I'll have to do a calibration run. It's just that with so few good nights to image on, sometimes it feels like a waste to spend one calibrating the focuser. I suppose the next hot day/clear night combo might be ideal, as I won't get any decent subs before 2300 anyway.
I like long subs for NB imaging, the longer the better. Limited to 30 mins as that's all my dark library is good for. Too much can go wrong with longer than 30 min subs, unless you're driving the HST.
Cheers
Stuart