Hi,
I tried the following experiment:
- Take 180 shots of 30 seconds each every 60 seconds with the 35mm kit lens that comes with my Canon EOS40D
- Align them via Star Alignment Process
- Stack than via Image Integration Process
The result of the stack is always something like the (particularly bad) example attached below: The center of the picture is reasonably good, the outer regions are distorted. The image shown is a stack of 10 pictures only. The single shots only show the usual 30 second drift lines in stars, not the strange explosion pattern seen in the integration image. I guess the reason for this is a combination of the following:
- the Canon lens is not free of distortions
- I am trying to stack plane representations of a sphere surface, which is obviously somewhat difficult (note that this is not an issue with the usual small fields that you get with 500mm+ lenses. The field of a 35mm lens is much larger.)
- When using Star Generator as a reference, I probably have to cope with the peculiarities of map projections.
I tried to resolve this as follows:
- Use Canon's DPP program to reduce lens distortion. Partially helped.
- Use Star Generator to create a map, use Dynamic Alignment to map one picture to this star map, use the resulting transformation to "un-distort" all images, align them, stack them (the result is what you see below)
- Use Star Alignment with increased RANSAC Tolerance (max value is 4) and/or 2-D spline surfaces. No real improvement compared to the plain stack, the reason probably being the fact that Star Alignment finds matched stars only in a small vertical stripe that gets smaller as the difference between reference and target image becomes greater.
Nothing really helped. I wonder if anyone out there has an idea how to handle the problem.
Enjoy your holidays!,
Georg
