Quote:
Originally Posted by Joshua Bunn
Hello Stephane,
First of all, you have resolved some good detail in those dust lanes.
A few questions...
How long was this exposure?
It looks like you do have some tilt in the image train somewhere, as the elongation of the stars is mostly in one direction. If the star elongation was radiating from the center out equally in all directions (or equaly in a circular direction at the edges all the way around the image), that could suggest a lack of tilt.
I say the elongation is mostly in one direction, because in the bottom left, the direction is a little different. This may suggest the trailing is not tracking (tracking issues would all be in the same direction)
Take a series of short 2, 5, 15, 30 sec exposures on a bright star field, this will tell you if the issue is tracking or optical in nature.
I would say looking at the image, its probably optical...tilt, flexure, corrector spacing, or a combination of them.
Cheers
Joshua
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Thank you Joshua for your response. This is a stacked image of about 40 x 300s exposures. I believe the elongation is worse on longer subs. The stars looked much better at 10s exposures (better, but not perfect).
I wonder if bottom-left and upper-right corners are a “destructive” combination: coma (elongation toward corner) combined with tilt in the other direction. Both combining at right angles to make blocky stars in the bottom left and upper right corners? Whereas in the upper-left and bottom right, both issues combine “constructively” to create very elongated stars.
Overall I am pleased with the detail in the galaxy. It’s just a shame the stars ruin this image. Hopefully I can fix this. Additional comments most welcome!!
P.S. Guiding was excellent at 0.6