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Question about eye relief/FOV

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Old Monday 29th January 2007, 11:16   #1
stubaldwin
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Question about eye relief/FOV

It's my understanding that, generally speaking, eye relief and FOV are often inversely proportional. What is the affect, if any, roof vs porro design has on this?
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Old Tuesday 30th January 2007, 04:07   #2
ceasar
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Quote:
Originally Posted by stubaldwin
It's my understanding that, generally speaking, eye relief and FOV are often inversely proportional. What is the affect, if any, roof vs porro design has on this?
"Often" is the operative word here--not "always." One example of the opposite effect is the notorious example of the ocular lenses used in the 7 x 42 roof prism binoculars in the 1980's in the Leitz Trinovid and the Zeiss Dialyt binoculars which gave both a very long ER and a very wide FOV. This seems to have been rather unique to the 7 x 42 format and did not extend to other formats like 8 x 42 or 8 x 32 where the ER got shorter when the FOV got wider.

It is my understanding that both ER and FOV are determined by the optical design of the ocular lens. I may be wrong, but I don't think the prism's used have much affect unless they change the effective focal length of the binocular by shortening or lengthening it. Maybe this is why some very wide 8 x porro's with oversize prism's like the Nikon 8 x 30 EII and Swift 8 .5 x 44 model 804 had short ER?

In any case, it is a subject that deserves some "enlightened" comment by our resident experts.

Cordially,
Bob

Last edited by ceasar : Tuesday 30th January 2007 at 04:26.
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Old Tuesday 30th January 2007, 14:11   #3
stubaldwin
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Thank you, Bob, for your response. I, too, would be very interested in hearing from our experts.
Stuart
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Old Tuesday 30th January 2007, 17:39   #4
eetundra
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Is ther also a relationship between field of view and depth of field?
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Old Tuesday 30th January 2007, 20:37   #5
John Russell
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Assuming adequate prism dimensions, FOV will generally be greater, the lower the magnification.
Assuming similar eyepiece designs, eye relief will increase with the focal length of the eyepiece.
As magnification is the ratio of objective focal length to eyepiece focal length and most binoculars, irrespective of their configuration have focal ratios around f/4.5, one could say that eye relief increases with objective diameter and decreasing magnification.
Of course, complex designs can increase eye relief in the same way that the front lens element of a telephoto lens can be closer to the film plane than its focal length or that the rear element of a wide-angle retrofocus lens can be further away from the film plane than its focal length.
Depth of field decreases with distance and increasing magnification, i.e. there will be no significant differences in depth of field between bins of the same magnification focussed on the same object.

John

Last edited by John Russell : Tuesday 30th January 2007 at 20:44.
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Old Wednesday 31st January 2007, 21:21   #6
John Russell
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Sorry, I should have written:-
Depth of field increases with viewing distance and decreasing magnification.
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