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celestron and back focus
After watching an interesting video on the NON EDGE celestron scopes, i decided to put it to the test.
When i first set it up i stuck to celestrons recommended 105mm back focus. This was to be measured from the rear of the reducer. They make a 50mm t piece which then allows you do do the usual 55mm on top of that.
What i found with this was that 1 the focal length of my C925 was not what celestron say it should be, which is 1480mm
When polar aligning with ASIAIR or plate solving it gives a focal length of 1319mm.
The other issue was the stars at corners where not very good.
So i kept reducing this back focus and am now at 81mm back focus, and this is getting me much closer at 1444mm and stars in the corners are sharper.
This was very interesting discovery for me, and at first i thought i was doing something wrong, but as i did more and more research, it would seem most people have found the same thing.
Obviously im not sure if this is the same for the EDGE models, but id be very interesting in knowing from any edge owner.
I am now going to do the same at the native focal length, to see what the results may be
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