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Old 27-12-18, 13:45
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petrochemist petrochemist is offline  
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Location: Clacton, Essex
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Originally Posted by BrittanyLogan View Post
You only have to move the focus ring a fraction of a degree to change the focus by many feet!
Although the thread is nearly ten years old, I think it only fair to point out this is actually the case for all lenses at the more distant end of the focus scale. Adjusting focus from distant stars to the moon (more miles than you can comprehend) hardly needs any focus adjustment at all In my experience the degree of focus movement with a mirror lens is not that different to a refractor of similar focal length. The design of the thread on the focusing helicoid being chosen to make it match the focal length. There is a range of focus sensitivities, some lenses giving more focus movement than others AF lenses tend to have less movement for a given change in focus, as precision in manual focusing is not so much of an issue.

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