View Single Post
  #2  
Old 02-08-2021, 07:30 AM
gregmc (Greg)
Registered User

gregmc is offline
 
Join Date: Sep 2018
Location: Sydney, Australia
Posts: 35
Actually, I think you have missed the main reason for polar alignment. If it was just tracking the sky, you could also do that on an Alt/Az mount with motors.

The reason it's needed is to prevent field rotation in your images. The camera needs to turn with the sky. This issue increases with the larger the sensor and longer the focal length.

On an EQ mount, the RA motor already should be turning at a rate to match the earth rotation and the dec motor doing nothing unless needed. Guiding basically does two things on an EQ mount. It bumps the speed to slow down or speed up the RA motor to match the earth rotation or bump the dec up or down to allow for any drift away from the movement of stars rotating around the celestial pole.

What is best is to polar align the EQ mount so that the RA axis is accurately pointing to the celestial pole. If you can see NCP/SCP, then programs like SharpCap is one of the faster ways of doing it. If you can't see the SCP/NCP then an app that does drift alignment is a slow way but the overnight build of NINA now has plugins, and a plugin you can get is the 3 star polar alignment that does not need to see either SCP or NCP.

Also, some mounts have a 3 star polar alignment in the handset but they rely on manual centering of each star. It's also best not to use a handset and replace the computing done in the handset with applications on a computer.
Reply With Quote