How accurate does Polar Alignment need to be?

[Jim Smith]

I'm sure I once came across a formula (or perhaps it was some tables) that allowed you to work out how accurate your polar alignment needs to be based on lens/telescope focal length, sensor pixel size and exposure time.

I've searched but not managed to find it. Can anybody point me in the right direction?

I'm planning to take 30 second exposures using a 500mm lens on a Nikon D750 ( 5.95 µm pixels).

I'm just wondering if being, say, 10 arcminutes off true polar alignment will be noticeable.

Thanks, Jim

 

[Thalestris24]

3 hours ago, Jim Smith said:

I'm sure I once came across a formula (or perhaps it was some tables) that allowed you to work out how accurate your polar alignment needs to be based on lens/telescope focal length, sensor pixel size and exposure time.

I've searched but not managed to find it. Can anybody point me in the right direction?

I'm planning to take 30 second exposures using a 500mm lens on a Nikon D750 ( 5.95 µm pixels).

I'm just wondering if being, say, 10 arcminutes off true polar alignment will be noticeable.

Thanks, Jim

 

Hi Jim 

For very short exposures at short focal length you don't have to worry too much about PA (see, for example, the 'no eq challenge' thread and others about alt-az imaging).

There is a calculator here should you feel the need . PA error will show up as field rotation over time. The calculator assumes you are guiding and field rotation relates to how far away a guide star is from the edge of your imaging fov. If you are not guiding, and just tracking on an eq mount, and taking 30s subs, then I don't think PA will be your limiting factor.

Louise

[Avocette]

You may find some help here also: https://www.cloudynights.com/topic/683609-polar-alignment-how-good-is-good-nuff/#entry9766007

[Jim Smith]

Thanks for the advice and links. It seems that my polar alignment does not need to be super accurate.