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Exposure times & field rotation considerations Alt-Az mount
Posted: Wed Oct 10, 2018 8:33 pm
by rpsutton
Hi All,
What is the longest exposure I can take using an alt az driven mount? also, I've been told that I can only take and stack so many exposures before field rotation will become a problem - what is that limit?
thanks
Patrick
Re: Exposure times & field rotation considerations Alt-Az mount
Posted: Wed Oct 10, 2018 11:19 pm
by oopfan
Patrick,
CMOS camera users generally take short exposures (i.e. <1m) so my guess would be not to worry about the effects of field rotation on a single frame. With regards to a stack, the stacking software will take the rotation out. The only side effect is that you will have to crop down your stacked image during post-processing more than if you had a GEM.
Brian
Re: Exposure times & field rotation considerations Alt-Az mount
Posted: Thu Oct 11, 2018 5:15 pm
by admin
Hi,
it depends on where in the sky you are pointing. Close to due E and W the field rotation rate is very small. Near to the zenith it becomes very very large.
You can read all about it here -
http://calgary.rasc.ca/field_rotation.htm
cheers,
Robin