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Old 30-07-2021, 12:34 AM
Martin Pugh
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Martin Pugh is offline
 
Join Date: Nov 2006
Location: Canberra, Australia
Posts: 1,339
Should a camera lens focus at infinity or close to?

Hi there.
Interesting observation. I am testing out a new lens which has a backfocus of 55mm. First I attached a QHY600 and all the necessary adapters to achieve 55mm, and the lens came to focus at infinity or very close to.

Changed the camera to a ZWO ASI6200, and all of the adapters necessary to achieve 55mm, and the lens came to focus 'significantly' away from the infinity mark on the lens.

The stars are not great, at all, even on axis. So I am wondering whether I should move the lens to infinity and then adjust the adapter length until the lens comes to focus at or near that point. In the hope that the star shapes come good.

Anyone experienced this?
thanks in advance
Martin
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