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Old 07-10-2015, 06:17 PM
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Tunnel Vision

AlexN is offline
Join Date: Mar 2008
Location: Brisbane, Australia
Posts: 6,708
It's since I added temp compensation. You wouldn't think it's required but the 300mm f/2.8 with 5.2um pixels and an all metal lens body = a noticeable focus shift with every degree of temperature change.

J-P Metsavainio told me that with his CCD on this lens his original sensor back focus distance was 1mm too short and the results were abysmal, once he added a 1mm shim he went on to produce 6 APODs and countless other perfect images with it. I didn't think removing the AA filter and the Uv/IR block would make that much difference however it was definitely enough. Like I said, before I modded the camera it was perfect right to the corners.

That 3rd image of ngc1365 and 17 of its more distant friends shows the weird rings perfectly. I did capture a new series of flats that made a big difference, and Don Goldman is making me a new filter for my 450D that will perfectly replace the two filters I removed in optical distance and I should regain my perfect stars.
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