Wednesday, January 15, 2014

Polar alignment, guiding accuracy, flatness with the new scope

With the Celestron EDGE scope, I was fighting a lot with guiding and flatness of the image (which was related to collimation). With the TOA-130 scope, I expected that flatness wasn't an issue anymore - though the large image area was concerning. But with the much larger and heavier scope, guiding could become a problem. And finally, with the much larger imaging field, I expected that I'd have to pay much more attention to my polar alignment, so that I won't introduce field rotation.

But none of these worries seem be justified:

  1. Guiding
    My guiding error is constantly <0.5 pixels (on the Lodestar) - mostly < 0.4. That's less then 1".
  2. Flatness of the image
    Here is the CCDInspector analysis for some of my images:

    3% tilt is pretty good. But it's weird that the image is tilted to one side. Here is another curvature plot from images that were taken on the other side of the mount:

    It seems as if my imaging train is somewhat susceptible to tilting. But again only a little bit. The image itself doesn't show any curvature in the edges!
  3. And finally polar alignment (and also flatness) of the image. Here are magnifications from the 4 corners of my image of the Rosette Nebula:


    What can I say? Round, pointy stars all around. No elongation into the corners (flatness) and no elongation around the center (field rotation)
Very, very good. I can now setup my scope. Do a quick polar alignment with the RAPAS - and off I go!