Field rotation question

[MortonH]

I've been told that an alt-az LX90/200 or similar will permit piggyback photography for a few minutes without field rotation becoming an issue. Can anyone point me in the direction of some guidelines of the maximum exposure versus focal length before field rotation becomes visible?


Thanks

Morton

[rogerg (Roger)]

If you keep the exposure times short (perhaps 30 seconds - 1 minute) and the field of view wide (about 50mm), and take many photo's (10+) you can then align and stack those in software like RegiStar, and not have any field rotation visible.

I have done this using a fixed tripod, not even a telescope.

Push those numbers further (longer exposure, etc) and you'll probably hit field rotation, but I am not certain on the theoretical limits.

[Gama]

Best method is trial and error.. Never fails.
Keep increasing exposure times until it starts to have trails.

[jase (Jason)]

Refer to the below link for star rotation formulas and examples:
http://www.astropix.com/GADC/SAMPLE7/SAMPLE7.HTM

[MortonH]

Thanks for the replies. Gives me a good idea, but you're right - trial and error is the best idea, if I ever get a scope!

Morton