Polar misalignment - Maximum exposure times

[mtodman]

OK, I've come to the end of my tether with trying to guide out the dec drift on my equatorially (wedge) mounted LX200GPS. I have permanently mounted my scope on a pier and have now achieved very good polar alignment (after much fiddling). I'm getting no noticable drift in 5 minute subs with Dec guiding turned off. The problem is that I am now very reluctant to remove my scope from the pier as I would need to go through the reallignment procudeure again.
I therefore have the following question.
Assuming that I only guide in RA, is there a way for me to work out the maximum single exposure duration I could achieve for a given polar misallignment before I notice elongated stars due to a drift in DEC? I assume a number of variables would come into play?
Polar misallignment amout
Focal Length
Imaging resolution (arc secs per pixel)
RA Position of object

Is there some lovely equation or software out there that can help me out?

Cheers
Matt

[rogerg]

Neither of my points answer your question sorry, but nether the less....

1) I work such things out by trial and error. It doesn't take much to get a feel for what works.

2) Why not guide in Dec? I guide in RA and DEC with my LX200 (classic) but due to backlash have guiding configured such that it only corrects in one direction in Dec, compensating only in the one direction caused by alignment error (I also get about 5 minutes without drift, but after that need to autoguide).

[JohnH]

Have a look at this .... might be what you are after...

http://www.iceinspace.com.au/forum/showthread.php?t=48397

[mtodman]

Indeed it does. Thanks very much John.
No doubt the light reading material referred to in the attached thread will put me soundly to sleep for many nights to come:).
Cheers
matt