Quote:
Originally Posted by GeeM
Russell would I be correct in thinking that the unwanted effects of field rotation could be reduced when imaging objects perpendicular to the axis of the earths rotation? I'm guessing I might be able to take longer exposures when the scope is tracking using primarily one axis. Is this what Raymo was eluding too in his previous post?
|
you are indeed correct in your thinking. there is even a formula for it:
The formula (not quite the whole story but pretty accurate) is:
Time (sec) = amount of rotation (degrees)*cos(Alt)/(0.004167*cos(Lat)*cos(Az))using the normal definitions of Latitude, Azimuth and Altitude.
0.1 degree as a rule of thumb for acceptable field rotation.
it is a balancing act however, shooting near the zenith (straight up) the dobs struggle to track accurately (and it rotates more quickly). shooting too close to the horizon you are going through too much atmospheric muck.
Quote:
Originally Posted by 1kmodem
With the Prime Focus on the dob, are you guys using any extender/Barlows/powermates?
|
I just used a coma corrector for deep space objects. when doing planetary however I use a powermate and sometimes a powermate and a barlow.