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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Binocular Conundrum: Field of View?
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Topic Review (Newest First)
07-04-2013 11:16 PM
noelex77
Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post
"The exit pupil is not on the retina. It has nothing to do with the retina. It is is the same position as the eyes pupil (technically slightly incorect, but close enough without confusing the issue)"
I understand that. But in this context, all eyeballs are the same size and all retinas are the same size, and that puts them all in the same position/geometry in relation to the exit pupil of the binocs. If the binocs had a 50mm wide exit pupil--it wouldn't matter because the iris would cut off the image at ~6mm and the retina can only accomodate a certain image size, no matter what angle the image entering the eye is "expanding" to.
The size of the retina is a limiting factor. The length of the eyeball is a limiting factor. The size of the iris is a limiting factor. The exit pupil size is another limiting factor--and the only relevant one that can be changed by the binoc maker, within limits.
)
The exit pupil does not limit the field of view.

Nor does the size of the retina, or the size of the iris.

The whole of the FOV passes through each point in the exit pupil. The exit pupil and/or the iris could be made minutely small and the FOV would be unchanged (but the image would be very dull)

The binocular manufacturer can modify the FOV without altering the exit pupil size.
07-04-2013 09:44 PM
tdw
Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by Cruisingdad View Post
Yep. Somehow it got dropped in the Kids forum. I blame TDW. Not sure why, but he makes a nice target.

Carry on!

Brian
Carefull CD or we'll bring speedo encased ape genitalia out into the open .... and you wouldn't want that now would you ?
07-04-2013 08:20 PM
hellosailor
Re: Binocular Conundrum: Field of View?

"The exit pupil is not on the retina. It has nothing to do with the retina. It is is the same position as the eyes pupil (technically slightly incorect, but close enough without confusing the issue)"
I understand that. But in this context, all eyeballs are the same size and all retinas are the same size, and that puts them all in the same position/geometry in relation to the exit pupil of the binocs. If the binocs had a 50mm wide exit pupil--it wouldn't matter because the iris would cut off the image at ~6mm and the retina can only accomodate a certain image size, no matter what angle the image entering the eye is "expanding" to.
The size of the retina is a limiting factor. The length of the eyeball is a limiting factor. The size of the iris is a limiting factor. The exit pupil size is another limiting factor--and the only relevant one that can be changed by the binoc maker, within limits.

Capta, I have purchased bincos. Many years ago. I'm looking for something a little different now, and I don't want image stabilized. There's moving parts and electronics and stuff to break in there. I was po'd when an internal lens (prism?) shattered in my binocs one winter, while they were stored in the closet. Apparently it was mounted ever so slightly too tightly and after enough years--the tension shattered it. Nice suprise, huh? So, I'll stick to the ones with no moving parts and just borrow or oggle yours.(G)
07-04-2013 06:06 PM
capta
Re: Binocular Conundrum: Field of View?

I'm a bit late on this thread, perhaps you haven't purchased a pair yet?
I broke down and paid the "big" bucks on the stabilized binos and am very happy I did. You can get more powerful ones (10 or 12 X magnification verses 8, the standard for small craft) as the stabilizing really does work and field of vision is not a factor when you can stay on target.
Again, this is another (of few) new items that greatly exceeds the hype, in performance.
My $650.00 8X50 rubber coated "marine" binos w/ compass never get used any more.
07-04-2013 06:30 AM
noelex77
Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post

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.)
?
The same comments apply to the exit pupil.( not surprisingly as this should coincide with the eyes pupil). All the image goes through all parts of the exit pupil. If we chop off part of the exit pupil we do not loose part of the image, the image just becomes less bright.

The exit pupil is not on the retina. It has nothing to do with the retina. It is is the same position as the eyes pupil (technically slightly incorect, but close enough without confusing the issue)

The exit pupil can be the same size with a very different FOV. We can reduce the exit pupil without effecting the FOV.

If we chop of some of the light in front or behind the exit pupil we will loose some image. This is why its important the position of the binoculars exit pupil ( the eye relief) at the the same position as eyes pupil, otherwise if the eyes pupil is smaller than the light circle parts of the view will be obscured so the FOV will be reduced.
This is why people using glasses need binoculars with a long eye relief. The glasses move the eyes pupil further back and the exit pupil of the binoculars must be also be moved back or portions of the image will be cut off.
The eye relief is the position of the exit pupil of the binoculars and this should match the position of the eyes pupil.
07-03-2013 05:57 PM
hellosailor
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?
07-03-2013 04:34 PM
Cruisingdad
Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post
Brian-
I don't mind the move at all, but "kids" has got nothing to do with anything. I posted the opening question in the General Interest / General Discussion area, unless the mouse slipped and dropped it elsewhere?
Although, it should show kids why they don't want to cut class when all those pointy geometry and trig things are being taught. (G) Personally I thought spherical trig was a special form of abuse, until years later when it made a whole lot of sense for celestial nav.
Yep. Somehow it got dropped in the Kids forum. I blame TDW. Not sure why, but he makes a nice target.

Carry on!

Brian
07-03-2013 03:32 PM
johnnyquest37
Re: Binocular Conundrum: Field of View?

Yes, same exit pupil diameter = same size image on your retina. What information that image contains is a function of the field of view. Larger FOV, you see more of the world. Smaller FOV, you see less of the world, but the cone of light on your eye is the same size.

It doesn't get any simplier than the formual provided. True FOV a direct function of field stop diameter in your case of otherwise identical binoculars.
07-03-2013 03:25 PM
noelex77
Re: Binocular Conundrum: Field of View?

Quote:
Originally Posted by hellosailor View Post
pappy, I understand what you are saying but I think you are missing something.

The binoc makers all claim that a larger exit pupil size is crucial, because the size of the exit pupil (or the iris, whichever is smaller) will "crop" the size of the image on the retina.

So, given that the image is being cropped by the same size exit pupil, which in theory means the same size image is falling on the retina, if the smaller FOV already produces an image that fills the retina, how can the larger FOV be presented onto the same retinal area? Unless the image size is reduced, which would mean a smaller magnification.

You see where I'm finding a contradiction in their logic? If you can fit a camel through the eye of a needle...don't you need smaller camels if you want to fit them through two at a time? (Do I get an award for most mangled analogy on that one?)
Its a good question Hellosailor
One fundamental mistake you are making is with the understanding of the pupil. The pupil does not effect the field of view.

All the feild of view passes through each point of the pupil.

As our pupil gets larger and smaller our field of view does not change.

This is true when viewing without binoculars (your field of view is not smaller in bright sunshine when your pupil is smaller) or with binoculars (once again the FOV with the binoculars is not worse in bright sunshine)

Another way of understanding the problem is to think of camera. As we stop the lens down we don't take a picture with a narrow FOV. We take the same FOV but some of the light captured by the camera lens does not get thought to the film. Despite blocking of some of the light we still get the whole FOV. We can make the iris bigger, smaller round or a funny shape and we get the same photograph just brighter or duller.

I hope this helps at least part of the puzzle.
07-03-2013 03:20 PM
hellosailor
Re: Binocular Conundrum: Field of View?

Brian-
I don't mind the move at all, but "kids" has got nothing to do with anything. I posted the opening question in the General Interest / General Discussion area, unless the mouse slipped and dropped it elsewhere?
Although, it should show kids why they don't want to cut class when all those pointy geometry and trig things are being taught. (G) Personally I thought spherical trig was a special form of abuse, until years later when it made a whole lot of sense for celestial nav.
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