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OK, I did a bit of preliminary work on this tonight, and shot the attached images.
I picked a magnitude 1 or so star through the clouds and shot a bunch of 1/10 second images with it both at the centre and top left of the frame. As I was not fully set up tonight, this was done on a camera tripod hence the very short exposures.
Attached we have the following images:
1. Star at centre of frame, Borg flattener
2. Star at top left of frame, Borg flattener
3. Star at top left of frame, WO flattener
As you can see, there is no appreciable difference in star frame at the top left of the frame vs the centre with the Borg flattener. Even the dimmer star to the right in the frames has good shape and no size change.
The WO flattener is a different story. While the star size is roughly the same, the astigmatism skews the light out into a diamond shape. Unfortunately the dimmer star was out of the top of the frame in these shots so I can't compare it.
I plan to do a full comparison this weekend if weather permits, with some wide star field shots.
Regards,
Eric
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