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Close Focus (1 Viewer)

lmans66

Out Birding....
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United States
Does 'close focus' change with diopter adjustments? ....I read someplace where it sounded like it did 'as their sentence was worded'..... jim
 
Does 'close focus' change with diopter adjustments? ....I read someplace where it sounded like it did 'as their sentence was worded'..... jim
Depending on the design, the diopter adjustment may consume some of the binocular's focus travel, so close focus or focus beyond infinity could be affected.
 
I suspect that the close focus distance specified by binocular manufacturers is a theoretical value.
This would be the closest distance between an object and the binocular objectives in which the rays from the image of that object would emerge parallel from the eyepieces, i.e. would appear to the observer as being at infinity.
As most users have the ability to focus at much closer distances, particularly the short-sighted and younger persons with a lot of accommodation (children with >10 dioptres), in practice the close focus distance achieved is usually significantly shorter than spec.
A binocular as opposed to a camera is an afocal instrument and focus is achieved by the users's eyes (retina=film or sensor), so the focus setting is dependent, not only on object distance, but also on the human eye.

John
 
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