Quote:
Originally Posted by Zuts
Hi,
Previously with my zwo 1600 mc pro I got reasonably round stars to the edge. I have a new camera, a zwo asi 2600 mc and now with the same other equipment i am getting eggy stars in one corner and stars with crosses in the other corner.
I have attached one 600 second light that has been stretched and debayered but no other processing.
The shot is from TV85, TV 0.8 reducer/flattener and asi 2600 mc pro, guided and no filters. I have also attached a zoomed corner.
Can anyone suggest what is causing the cross like stars?
Thanks
Paul
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Hello Paul,
It's more than likely caused by the fact that the larger sensor in the ASI2600 (approx. 28mm senor diagonal) coupled with your use of the reducer allows the sensor to see closer to the extremes of the now reduced image circle. This would not have been as evident when you were using the smaller sensored ASI1600 (approx. 22mm sensor diagonal) as it would see less of the image-circle extremes. Over and above all that there is always the potential for some tilt to accentuate issues on one side/corner.
It would be useful to know the native image circle of your scope to help nail this for certain as it is not listed in any specs I could find, but I have read that the scope does not seem to support a fullframe
* image circle, and when attempted results in misshapen stars/abberations.
If you can tolerate the native focal length, try not using the reducer as this will result in a larger image circle and potentially fewer edge or near/edge image-circle abberations for the larger sensored ASI2600 to see.
Best
JA
* EDIT: I've often noticed that for medium to smaller scopes that don't support a full-frame ~43mm image circle, they support something around 30-33mm.
If that's the case with the TV85 and it has a ~33mm image circle, then when you add an approx 0.8x optical reducer, the image circle will become ~26mm. That's smaller than the ASI2600 sensor and not a perfect match for its 28mm diagonal sensor
unless you are happy to crop because otherwise you will see vignetting and abberations in the corners.