Polar alignment and auto guiding

[baggywrinkle]

How accurate does the polar align have to be if you are using auto guiding?

Seems a silly question but one that is puzzling me.

[Leveye]

The better the alignment the better the guiding the better the picture.

[sidelight]

As I understand it the alignment should still be as accurate as possible.  If you are out then there may be field rotation at the edges with a long exposure, and why make the guiding work harder than it needs too.  In reality the guiding should be making as few adjustments as necessary to "help" the mount tack the object, it doesn't replace polar alignment, it compliments it.  That said I have to set up and pack down my gear every session so I have to balance the alignment accuracy with actually taking some shots, sometimes it ends up better than others 

Cheers

Ross

[baggywrinkle]

Thanks folks. Much as I thought....no short cuts or everyone would be doing it. It is getting that balance of time available, dodging clouds, etc, etc.

[Chris Rowland]

Once you are guiding the remaining uncorrected error is field rotation.  Covington says that for declinations less than 60 deg the maximum rotation rate in arc minutes per minute is the same as the polar align error in degrees.

What this means is that if you can get your error to 10 arc minutes or less the field rotation rate will be less than 10 arc seconds a minute.  This is relative to the guide star so you can easily calculate what the maximum shift in pixels this will give you. I make it 1.2 microns a minute at a distance of 25mm.

What I do is an ASPA and get on with imaging.

Chris