Polar AlignmentPosted By Mike Shade |
For precise polar alignmentyou need to do a drift alignment. Also something that you might think of is what is you mean photographic declination? For me here in SE Arizona, it is about +22, for somewhere further north, it will be higher. Basically what this does if average out your drift for most of the sky. You will not be shoooting pictures at -50 declination and probably not a +80 either so you need to find your "average" which is partially based on your latitude.
So, assuming that you are aligned reasonably well north, point the scope to your mean photographic declination and the meridian. you will need a high power guiding eyepiece with illuminated crosshairs. Align it so that when you move in Dec it moves on on line and RA moved the other line. Also note which way is north and south IN THE EYEPIECE. find a star and set in on the N/S line and watch it drift in declination only and note its direction of drift. If the star moves north, move the scope toward the east, if the star moves south, move to the west. hopefully your mount will allow you to make small adjustments. Adjust untill there is no drift for 10 minutes. Now point the scope over low in the east, keeping it at your mean photographic declination (only move in RA). Again figure out which way is north/south in the eyepiece, center a star on the N/S line and watch drift. If it drift north, adjust polar axis down, if it drift south move polar axis up. Again there should be no drift in 10 minutes. Now go back to the meridian and do it again but shoot for 20 minutes with no drift, then go back to the east.
Also keep in mind that if you need to move the scope a bit to find a bright star that is OK but no more than like 1/2 degree, less if possible. Also when you are drifting keep in mind your starting position and don't get too far from it. You might need to move east and find another star. Also, keep in mind that this procedure can take a bit of time but when done you will have a very accurate polar alignment.
Mike
So, assuming that you are aligned reasonably well north, point the scope to your mean photographic declination and the meridian. you will need a high power guiding eyepiece with illuminated crosshairs. Align it so that when you move in Dec it moves on on line and RA moved the other line. Also note which way is north and south IN THE EYEPIECE. find a star and set in on the N/S line and watch it drift in declination only and note its direction of drift. If the star moves north, move the scope toward the east, if the star moves south, move to the west. hopefully your mount will allow you to make small adjustments. Adjust untill there is no drift for 10 minutes. Now point the scope over low in the east, keeping it at your mean photographic declination (only move in RA). Again figure out which way is north/south in the eyepiece, center a star on the N/S line and watch drift. If it drift north, adjust polar axis down, if it drift south move polar axis up. Again there should be no drift in 10 minutes. Now go back to the meridian and do it again but shoot for 20 minutes with no drift, then go back to the east.
Also keep in mind that if you need to move the scope a bit to find a bright star that is OK but no more than like 1/2 degree, less if possible. Also when you are drifting keep in mind your starting position and don't get too far from it. You might need to move east and find another star. Also, keep in mind that this procedure can take a bit of time but when done you will have a very accurate polar alignment.
Mike
