Quote:
Originally Posted by Starkler
To gain meaningful results you would need to have perfect polar alignment  |
Hi Geoff,
Thanks for the post.
As I have mentioned several times before, including on IceInSpace,
the concept of "perfect polar alignment" is a myth and is widely misunderstood
by amateur observers.
Due to the effects of atmospheric refraction, there is no magic point in the
sky to which one can align the polar axis of the scope so that when the
scope rotates around the polar axis only, field rotation will no longer exist.
At best, for any one fixed point in the sky, there is a corresponding optimal
elevation of the polar axis. Unless one has an observatory at the North or
South Pole where the polar axis then corresponds exactly with the zenith.
As a whole sky compromise, it is optimal to align with the refracted pole
rather than the true pole.
However, before rushing out and adding an electrically controlled
jack that will dynamically adjust the elevation of the polar axis, which is one
way to solve the problem, or moving to the North or South Pole, which is another
way to lick it, then if autoguiding is used, the field of view not overly large and
the imaging time kept appropriately short enough, then from a practical standpoint,
there will be no problem.
But as for looking for that "perfect polar alignment", unfortunately there are
only two points on Earth from which it might be done and as for the rest of
us, like most of life, all one can do is reach some best compromise.
Best Regards
Gary
