Binocular Conundrum: Field of View? - Page 2 - SailNet Community
Old 06-24-2013
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Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post
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.

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Re: Binocular Conundrum: Field of View?

Oh, gravity I canunderstand. In Newton's memoirs he states it was a story he made up to hide the real truth, which is that dogs like table scraps, and the only way to guarantee table scraps will fall down, is by creating gravity. So when you see dogs "sleeping" all day, that is not sleep, that is the hard work of ensuring that everything falls DOWN to where the dogs can get it.

And if you think that is any less likely than "physics" you go explain Bose-Einstein Condensates or why one particle can be split and exist in two discrete places at the one same time. Brookhaven Labs proved that one about 15-20 years ago, spin 'this' particle and "that" one moves with it--despite the absence of any physical connection that we can observe.

So...FOVs...Yeah, when the numbers don't add up, there must be a politician in the room.
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Old 06-28-2013
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Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post
tim-
I'm talking about ONE manufacturer, giving a 50% wider FOV for two different "same numbers" binocs they make. So however they define FOV, it is THE SAME definition, from the same maker, for both binocs.

Auspicious-
Same thing. I'm not comparing apples to oranges, I'm saying that it doesn't matter which glasses you compare. 7x50 to 7x50, or 8x42 to 8x42, pick ANY SIZE you want and then compare two different bincos IN THAT SAME NOMINAL SIZE. Whether they are made by the same maker or two different makers, but the SAME NUMBERS on both glasses. As I said, I'm familiar with optics, I know pretty well that a 7x and a 10x will--or at least should--have very different FOVs under most conditions.

HyLyte-
I'm still not understanding this. First off, I'll assume when you say the length between the front and rear lens you mean the length of the optical path, since that can be folded differently. But even so, if the magnification is the same, and the size of the image coming out the back is the same (as measured by the exit pupil), then the distance shouldn't matter. Same is same, if the apparent view is 10x "bare eye" sized, you can only blow things up so far UNLESS you change the size of the image. So in theory a wider FOV would require a wider exit pupil image. That exit pupil image "crops" whatever the apparent FOV is going to be, doesn't it?

Doesn't make sense, unless the exit pupil becomes a meaningless number.
I think I see the assumptions that are leading you astray:

The exit lens doesn't crop the image, it just focusses the image for your eye. the far lens is what crops the image. For a wider FOV the outer lens would have to be closer to the pupil lens, or wider, while the pupil lens can stay the same.

Therefore if the far lens is closer to the pupil lens, the field of vision angle is short and _wide_, vs being farther away where the FOV angle gets longer and _narrow_, as the finger-loop demonstration shows.

What is being moved in the finger-loop demonstration is the far lens.

Does that help?

Last edited by groggy; 06-28-2013 at 05:03 PM.
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Re: Binocular Conundrum: Field of View?

Not really groggy. I'm still stuck on the exit pupil being the same size, the eye relief being the same or very similar, and as a result the geometry, the size, of the image being put on the retina is going to be the same size.

If the "reality" is 100 feet wide, and the image on the retina is, let's say 10mm wide, then the apparent magnification is fixed and the only way to change the FOV is going to be by changing something, which will either result in a different magnification, or a reduction in the size of the image on the retina.

If all these binocs have the same "night factor", the same apparent size image as fixed by the exit pupil size, the iris, the retina, then they cannot have different FOVs. In order for the FOV to change, the magnification has to change (and they all say it doesn't) or the size of the image on the retina has to change. And they all say that's limited by the exit pupil size.

I'm no math ace, but either the binoc makers are tlaking in tongues, or there's something they just don't talk about which is in fact changing, along with the FOV. And for the FOV to change by 50%, the image on my retina has to become 50% larger as well, and that would mean some significant change in the back of the binocs. Exit pupil, eye relief, something has to show a similar huge change.

Or, they're all cooking the books with the numbers. You know, like "this boat sleeps eight!" Sure, as long as that's Snow White and her little friends, two to a berth. (G)
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Old 06-28-2013
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Re: Binocular Conundrum: Field of View?

simpleist the higher the magnification {first #) the narrower the field of view. Optical coatings and multiple internal optics can change this slightly at a significant cost.
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Old 06-29-2013
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Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by MarkofSeaLife View Post
I have been led to understand that 7 times magnification is best for sail boats but now with image stabilization higher magnifications are better.
As Auspicious says, then one needs the wider lens to let in more light.

If you are thinking about a new pair you might want to look at the extra \$\$ for stabilization and see if you think its worth it.

I realise neither of us are really addressing the issue at hand but methinks you are making a good point.

We recently purchased a pair of Canon 10x30 stabilised and am quite convinced of their advantages. Went 10x30 as they were a good entry point dollar wise to the world of stabilised but almost certainly will go up a size or two when/if we buy a second pair. I loath almost every Canon product I have ever bought except for their cameras, thankfuly the binos seem to meet the camera standard and not match their lousy printers. ymmv. I'd think that something around 10x50 would be exceptional.

Cheers

Andrew B

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Re: Binocular Conundrum: Field of View?

"simpleist the higher the magnification {first #) the narrower the field of view."

As a sweeping generality, yes. Now take a Nikon Monarch 5 10x42 and a Nikon Monarch 7 10x42, both with 4.2mm exit pupils, both 10x with a 42mm objective lens. The FOV for the M7 is stated as fully 50% wider than it is for the M5.

Perhaps the magnification for one of them has been grossly mis-stated? No, there's something else "wrong" here. (Not to pick on Nikon, it isn't just them.)
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Old 06-29-2013
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Re: Binocular Conundrum: Field of View?

Suggestion: Email several manufacturers and ask the question, then get back to us. It's better to have it in writing than to hear them explain it over the phone.
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Re: Binocular Conundrum: Field of View?

Yeah, email these days isn't used, everyone (?) wants you to register an account and post it to their forum. More scuttwork. And half of that is answered by agents who only think they are speaking Ynglitch.

But eventually I'll pin it down, and get back to you.
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Old 07-01-2013
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Re: Binocular Conundrum: Field of View?

I kinda skipped the last few posts so, I don't know if this was mentioned or asked but look at it as though it was a zoom lens, same glass both ends but the difference in length between both ends determines the FOV; shorten the lens the wider the FOV, extend the lens the narrower the FOV, same optics but different effect so, the question is, are the dimension on both binoc barrels the same. I know it takes very little movement on one of my lenses to change the FOV

Another thought, all things being the same, maybe the objective lens has a more pronounced fisheye cut to it, giving it a wide FOV

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Last edited by poopdeckpappy; 07-01-2013 at 10:55 PM.
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