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Old 07-03-2013
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Re: Binocular Conundrum: Field of View?

Brian-
Well, considering the eight or ten seconds it took while my page moved around and reloaded THREE TIMES just now, thanks to all the crapware from advertisers who need to be housebroken (or horsewhipped, please?)...thanks for the cleanup.

And now back to our main program.

noelex, you totally misread me. I never mentioned the pupil, as in the pupil of the eye, as being a factor in this. What I said was the the EXIT PUPIL of the binocs is all the same, and THAT is stated to be a limiting factor by all the binoc makers. That is, the field of light coming out of the binocs is constrained to a circle 4.2mm in size at the point where is focuses on the retina. (At least, that's how some of them define it.)

Just got off the phone with perhaps the most highly respected brand name of German glass and their answer was "well we use extra-dispersion glass instead of...and..." in other words, they hadn't got a clue as to what FOV even was.

So I fired up the inverse tanget finagler, which says the difference between some of the FOV numbers (like 268/336/375 which seem to represent the spread for 10x42 glasses from multiple sources) correspond to a difference of 5.11d/6.21d/7.32d in terms of the degrees of the actual conve of vision in the binocs. A plus-or-minus one degree change would account for the different FOV, but that also would change the magnification from roughly 9x to 12x as well. Given, again, that the size of the image on the retina is a fixed and limiting factor for all of these.

Now, if they are full of FUD, it is also possible that the narrower FOV glasses will simply present a black ring around the image, rather than filling the retina. That would explain it very simply, allowing for the "exit pupil" to remain the size size, if they are defining "exit pupil" incorrectly and somewhat misleadingly.
Looking at my own 7x50's, which claim a 366 foot FOV, there's a black outer ring, so maybe the ones with the narrower FOV simply have bigger black rings? And the gentle manufacturers are trying to ignore mentioning their bonics often have tinier images?
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