http://www.covingtoninnovations.com/astro/Polar.htmlhttp://www.covingtoninnovations.com/astro/Polar.html

또는..

Here's an equation for the accuracy required for polar alignment:

E = 750 * S * cos (D) / ( T * F * A)

Where:

S = worst case length of trailing allowed in microns
D = declination of the object being imaged in degrees
T = time duration of the exposure time in minutes
F = focal length of the system in mm
A = sky angle between the guide point and furthest part of image in degrees E = required accuracy of polar alignment in degrees

A second useful equation is:

R = 0.262 * E

where:

R = Drift rate of a star in arcseconds per minute (without guiding) E = polar alignment error in degrees

The first equation lets you determine how close you must be when drift aligning and the second lets you know if you've achieved that level of accuracy. Using my STV, I simply set the dec axis agressiveness to zero and use a timer to figure the approximate drift rate. The STV lets you detect drift very rapidly and also measure it since it reads out in arcseconds. This can be done with a reticle eyepiece but it takes longer and is less accurate.

There is an excellent paper by R. N. Hook in the British Astronomical Association Journal 2/89 from which I derived these equations. Hook presented results for 30 micron trails but this was easily generalized.

Steve...