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Old 30-10-2019, 07:06 AM
Stefan Buda
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Stefan Buda is offline
 
Join Date: Jul 2013
Location: Melbourne, VIC
Posts: 823
I think the changes you see when you rotate the mask are due to the fact that the the entrance pupil is displaced relative to the center of the mask for stars in the corner of the field. The orientation of the mask should not matter for the center of the field.
I find that a Bahtinov mask is surprisingly sensitive device for detecting on axis astigmatism. If you focus on a star in the center of the field and then check the focus for different orientations of the mask you will see differences if astigmatism is present.
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