I have the most recent versions of CCDIS and CCDS and have used the CCDIS alignment feature with great success. It works as good as Registar for my STL11k frames but it will not align my 16803 frames. I am using a AP155EDF at f/5.4 and so there are generally tens of thousands of stars in each 16803 frame. CCDS says that each frame is aligned (p= 0.0020 or better usually) but after stacking the stars in each of the corners are clearly not aligned. The stars in the center of the frames are aligned.

If I use Registar the frames align perfectly.

Should I do anything differently?

Tom

Hi Tom,

This is a problem caused by non-linear distortions in your optical system in combination with a large chip. The larger the chip, the greater the aberrations near the chip edge.

The problem occurs more frequently when one tries to align images that are acquired by different optical systems, or by the same system but with images offset from each other by a significant amount. CCDIS and CCDStack currently support only linear transformations of images during alignment. This means the images are shifted/scaled/rotated/flipped, but never distorted. To handle the non-linear alignment will require image distortion.

Non-linear aberration are smaller closer to the center of the optical path, so the alignment works better near the chip center. The further away from the center you look, the more the star positions will not coincide. How big of a problem this is will depend on how well-corrected the optics are and how large the chip.

Stan and I have been planning to address this in a future release of both products. If you'd like, please upload two zipped frames that demonstrate this problem to a website, and e-mail the link to download them to:

paul [at] pk.darkhorizons.org

I'll verify that non-linear aberrations are the problem. This will also help us in the development of the new algorithm (which actually already exists in prototype form).

Regards,

-Paul

Thanks Paul. I'll see if I can get you the files.

Tom