Came across this technique in the MaximDL how to guides ...
Paul Boltwood has pioneered a very simple and effective technique for polar alignment. Using a planetarium program, create a chart of the area around the pole (north or south). Make sure that the proper pole location is labelled on the chart.
Next, do a rough polar alignment, and then take a 60-second CCD image of the pole. Halfway through the exposure, rotate the telescope about the RA axis as far as it will go. Move it just fast enough to complete the arc in 30 seconds. You will create an image with the stars clearly visible, plus a set of near-circular arcs centered on the position of the telescope’s pole. You can now easily see the difference in position between the telescope’s polar axis and the correct pole location. In fact, you can measure this distance in X and Y using the Information window, and get a very accurate number. Now adjust the mount by that distance (tip: set a rapid binned exposure mode and watch the stars move as you adjust). After one or two iterations you have an extremely accurate polar alignment.
I do something similar but visually ( with a fork mount )
The final aligning requires the OTA to be at exactly DEC = -90
but you need to get close first,
i cheat a little
I have 2 finder charts, one for my finder and one for my EP
I just set my DEC axle horizontal and look in the finder till i can see where
the pole is. I adjust the wedge in AZ only till i centre the pole asterism in my EP. If necessary, i use the DEC slomo to centre the view, but i am only interested in the horizontal alignment first.
Then i rotate the scope 90deg in RA and repeat, but this time i centre the asterism using the wedge alt adjust, and the DEC slomo again
Once this is done, you are within a few arcmins of the pole and can go to the spin test to refine it.
Note. If yr OTA is not parallel to yr RA axis when the DEC is at -90
you cannot get pure circles, so you have to test that first
Came across this technique in the MaximDL how to guides ...
I'm working on some software to facilitate doing this in real time with the Canon Live View mode via a USB connection. If I ever get anywhere with it, I'll be posting it on IIS.
