Field rotation calculator

[montewilson]

Guys - Does anyone have a field rotation calculator? I would like to know what the maximum acceptible polar alignment error is for a given CCD, focal length, exposure and declination.

I have a Tak FSQ with an STL which may be some people's idea of heaven but it's not all roses. Field rotation is a harsh mistress with such a big, flat and sharp field. I have been drifting for years but am gearing up to take on the polar scope on the EM-200 mount and want to know if the 2 arc mins it can achieve are enough to get me out of trouble for 15 min exposures. My arcs/pixel is 3.

[Dennis]

There is a comprehensive mathematical analysis of polar axis misalignment in Michael Covington’s book, Astrophotography for the Amateur, 2nd Edition.

It covers:

Hour angle error
Declination error
Field rotation

The author’s website also has a calculator at:

http://www.covingtoninnovations.com/astro/astrosoft.html

Cheers

Dennis

[montewilson]

Dennis !! We have to stop meeting like this!

I have had a look at the calculator and it tells me that if I get within 2' of the pole with the PAS I should have trouble free imaging up to 15 mins. I will do a bit of trig later to confirm it but so far it looks good.

Thanks for the attention and the xls too.