Gentlemen,
I was recently enlightened about polar alignment and drift in the two axis on the Astro-Physics group.? The polar alignment most of us are used to is designed to provide minimal declination drift, not minimum RA drift.? If we were on the moon there would be no difference.? But due to atmospheric refraction, the minimum declination drift polar alignment results in RA drift.? What Roland Christian recommends is to align the azimuth in the normal fashion minimizing declination drift at the celestial equator and the meridian.? But instead of going East or West to do the elevation adjustment, move? up the meridian to the zenith.? Then adjust the elevation to minimize the RA drift.? Good PEC helps here to identify the RA drift. ?
The difference is that the old method was designed when scopes typically did not have a declination adjustment that could be used in guiding, but the RA could be adjusted for guiding.? So the polar alignment routine was designed to minimize declination drift over the entire sky.? With scopes that can effectively guide in declination, the new polar alignment routine minimizes both declination and RA drift within 30 degrees of the meridian, where most imaging is done.? This can allow for unguided imaging in this range and is still readily guided outside of this range.
I have yet to try this, but the theory seems sound.? Rolando would not steer me wrong.
Greg
