Albert van Duin
Member
I tested my new Samyang 135mm T2.2 lens with a Baader modified Canon 5D MKII. 30, 30s exposures at allmost full opening and 400 ISO.
Please find attached a non calibrated and calibrated stack (dark, bias, flat), both treated with ABE in PI to flatten the background.
In both images you can see a donut, a bright one in the uncalibrated and a dark one in the ucalibrated version.
The uncalibrated one was over-stretched to show the donut.
When I look at the master flat, over-stretched, There is no donut.
What could be the cause of this? Maybe light entering the viewfinder of the camera?
Also the sky was not completely dark, twilight keeps going here this time of year and the moon was still up on the other side of the sky.
I also had a protective UV-filter mounted on the lens.
Any insights are welcome.
Thanks!
Albert
Please find attached a non calibrated and calibrated stack (dark, bias, flat), both treated with ABE in PI to flatten the background.
In both images you can see a donut, a bright one in the uncalibrated and a dark one in the ucalibrated version.
The uncalibrated one was over-stretched to show the donut.
When I look at the master flat, over-stretched, There is no donut.
What could be the cause of this? Maybe light entering the viewfinder of the camera?
Also the sky was not completely dark, twilight keeps going here this time of year and the moon was still up on the other side of the sky.
I also had a protective UV-filter mounted on the lens.
Any insights are welcome.
Thanks!
Albert