Question about polar alignment and guiding.

[Auspecial]

Hey all,
I am yet to even purchase any astrophotography equipment bar my 200mm lens and trusty tripod. Despite this I was wondering if guiding negates the need for a good polar alignment, as the mount is always 'watching' the guide star? Or does a good polar alignment mean the guiding setup has to do less work?

Cheers.

[Anth10 (Anthony M)]

I don't use autoguiding yet, but I've read and understood that it is a necessity to achieve as accurate polar alignment as possible.
As you suggested it assists the guiding software and keeps the corrections to a minimum. Some even perform what's called a manual drift alignment after setting up their scope prior to autoguiding as this improves the performance also.
Hope this helps.
Good luck.

[doppler (Rick)]

Auto guiding moves the scope after the star has moved so is always chasing alignment, so the better the polar alignment the less work the guider has to do and you get tighter/sharper images.

[Auspecial]

Great, that's what I thought may be the case. Thanks for your inputs.

[OzEclipse (Joe Cali)]

If your scope isn't well polar aligned but is well autoguided, the star you are autoguiding on will be a point, all other stars will trace circles around that star.

How long? Depends how inaccurate your polar alignment is, the focal length of optics, distance of the guide star from the image field, and length of exposure.

Celestial wonders has an online calculator that will let you put in the values

http://celestialwonders.com/tools/ro...ErrorCalc.html

Examples
ED80 600mm focal length,
polar align error -1 degree from true pole
guide star 2 degrees from image field
5 min exposure
Trail length 8 microns (about 2 pixels)

ED80 600mm focal length,
polar align error 5 degrees from true pole
guide star 10 degrees from image field
5 min exposure
Trail length 40 microns (about 10 pixels)

Telephoto lens 200mm focal length,
polar align error 5 degrees from true pole
guide star 10 degrees from image field
5 min exposure
Trail length 67 microns (about 16 pixels)

You can do your own experiments with different lenses and parameters.

Joe

[Auspecial]

cool website, thanks