tenex
reality-based
This subject has come up in a couple of recent threads and seems worth asking about more directly: I don't use eyeglasses with binos, and have the impression that what I'll call my perceived field of view (PFOV) -- how immersive the view feels, how much I feel I can see vs the black space around it -- suffers from two recent trends, high eye relief and field flatteners. And yet neither one is a factor in the equation that defines "Apparent FOV", which is only a function of real field and magnification. That has tended to confuse discussion of the issue for me.
In the case of FF, I think I can envision how this works: a curved field seems a bit bigger subjectively because things get stretched at the edges, while a flat field irons that out. I presume this is why I've read that the ISO formula for AFOV, which gives a slightly smaller result, is more accurate for FF binos while the simpler approximation has always been good for classic designs.
Regarding ER, I have the impression that among binos I've tried, those with around 13mm ER or less (maybe up to 15mm or so) give me a more immersive view, while ER approaching 20mm as in many models today gives more of a tunnel-vision effect. Ideally I mean this other things (magnification, RFOV) being equal, though in practice that probably hasn't quite been the case. But again it makes sense to me that you can't increase ER indefinitely while maintaining an immersive view.
Do I have this about right, and can anyone offer further technical explanation? Or is it the case that high-ER designs actually wind up limiting the real FOV, and thus the apparent as well?
In the case of FF, I think I can envision how this works: a curved field seems a bit bigger subjectively because things get stretched at the edges, while a flat field irons that out. I presume this is why I've read that the ISO formula for AFOV, which gives a slightly smaller result, is more accurate for FF binos while the simpler approximation has always been good for classic designs.
Regarding ER, I have the impression that among binos I've tried, those with around 13mm ER or less (maybe up to 15mm or so) give me a more immersive view, while ER approaching 20mm as in many models today gives more of a tunnel-vision effect. Ideally I mean this other things (magnification, RFOV) being equal, though in practice that probably hasn't quite been the case. But again it makes sense to me that you can't increase ER indefinitely while maintaining an immersive view.
Do I have this about right, and can anyone offer further technical explanation? Or is it the case that high-ER designs actually wind up limiting the real FOV, and thus the apparent as well?
Last edited: