Old as Dirt!
Join Date: Nov 2008
Location: Tampa Bay Area
Thanked 147 Times in 139 Posts
Rep Power: 8
Re: Binocular Conundrum: Field of View?
Homer, the finger loop analogy falls short to me.
If the exit pupil size is supposed to correspond to the final size of the image on the retina, we have a fixed size image, let's say 5mm. That's at one end.
On the other end, we have a fixed life-size image. If we are viewing that image at "life" size, magnification 1, the FOV and the image on the retina are always the same, regardless of the finger loop blocking it. The finger loop effectively becomes the apparent exit pupil size, and a smaller FOV only happens with a smaller apparent exit pupil.
Since the eye relief and the distance from the retina to the exit pupil image are pretty much the same on all the binocs...I just don't buy the finger loop moving around as being analogous to what happens with binocs. Maybe I'm too dense to see it.
From what the binoc makers would have us see, everything behind the back lenses of the binocs is the same. Everything from the front lenses to the image is the same. And you're saying, if the only change is the length of the internal light path, that can account for a 50% change in the width of the FOV?
This must be why I wasn't a math major. Here, have another flagon of wine and try again. Please.
I do not believe I can make the principal any easier to understand and so, shall pass. I suggest you just pick whatever instrument seems to meet your requirements and forget details you can't/won't understand. One could also argue the principal of Gravity which some do not understand and view as irrational. Maybe, but, if you pick up both your feet at the same time in defiance, I can assure you, that you will end up on your butt.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."