Astrophotography at the Veluwe Logbook, results, lessons learned

New polar alignment method

Not really new, ofcourse. There are a few specialised commercial and public domain packages that use the same principle. Check out PolarAlignMax and Tpoint.
I got inspired by reading about Astrometry.net. They do "blind solving" of astrophoto's. That is pretty cool. Read about it here http://cosmo.nyu.edu/hogg/research/2006/09/28/astrometry_google.pdf

My method in short:

1. Aim the mount's polar axis at Polaris. As accurate as possible, but spend no more than 1 minute.
2. Put a camera on the mount with a medium telephoto lens (I use 135mm)
3. Take 3 or more photo's. Between the photo's: sweep the mount in RA in considerable amount, but do not move in DEC! Write down the time of each image
4. Do a blind solve of all images. I use Elbrus (offline) or Astrometry.net (online)
5. I write DEC and RA and time measurements in my Excel spreadsheet.
6. The spreadsheet  uses Excel's  "Solver" to calculate  the Azimuth and height misalignment of the polar axis.
7. By using Azimuth and height finetune knobs I then can change the direction of the polar axis to correct for the misalignment.
8. Repeat the above steps starting from step 3 for another iteration and higher accuracy.

I will try to use this method to obtain a polar alignment error of less than 2' within 20 min.

I will report about my results here!

Edit sep 2 2010: I tried to determine the accuracy of my method. I did 6 series of 5 measurements without changing Azimuth and Height and thus found 6 separate polar alignment error (in degrees)  for Height and Azimuth.

So it follows that my method has an error of less than 0,15 degrees, about 8 arcmin. I think I can improve on this using larger sweeps on the sky within a serie and by using a telescope instead of a 135mm telephoto lense. The accuracy might improve too if I do the sweeps with the RA-motor instead of of manually after decoupling the motor.

But first I need to get Elbrus working with images taken with my 550mm telescope. They have a smaller pixel scale and Elbrus cannot plate solve then, yet.