PFOV concept (1 Viewer)

elkcub said:

I'm a perception guy.

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So am I, Ed. :-O

elkcub said:

Needless to say there is quite a distance between our understanding of things.

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I'm not sure there's an abyss between our understandings. We may only put different emphasis on some things, then misinterpret how much emphasis the other guy puts in things. And remember I said I may be wrong.
Anyway, I'll try to explain my line of thinking.

elkcub said:

Focusing an optical image over the retina is one thing, and having the neural apparatus to resolve fine detail in a particular retinal area is another.

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Yes, and hopefully you've noticed that I mentioned the two central degrees of sharpness. See also the diagram on the distribution of visual acuity:
http://en.wikipedia.org/wiki/Fovea_centralis

What I'm saying is that the optics of the eye are far from perfect, so even if we did have a greater portion of the retina literally packed with cones, the aberrations of the eye would be the limiting factor for our visual acuity.
Of course, more so the further into the periphery of the retina we go.

Undeniably, we're able to detect peripheral zones [periphery of the retina, that is] of decreased sharpness when looking through a poor telescope. Partially this is due to the movements of the eye, but also that the brain detects when there are other aberrations than what it is used to see.

During the first year in life, visual acuity increases very much. And the brain learns how the physical world relates to the retinal image.
This experience is the foundation to the amazing correctness by which most of us can assess the surroundings. Despite the vast optical aberrations and the low density of cones in the periphery of retina, the brain is able to compute the cues received from the eye.
Thus, the peripheral acuity and judgement of object's size and location are greater than could be expected from the anatomical organization of the eye.

elkcub said:

But why on earth would the sun "boil the [peripheral] retina in seconds" if images were focused there but not at the fovea? I take it you actually believe this to be true — with or without glasses. Good grief!

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Staring at the Sun for more than a fraction of a second will cause permanent and severe damage to the fovea. The small, focused image of it literally boils the retina. Not staring at the Sun is a reflexive behavior aided by the painful muscle contraction of the pupil.

But somewhere beneath the Sun, let's say 15 to 30 degrees off-center, we can keep the fixation, at least with some strain.
I still believe that if the peripheral parts of the retina had a focused image of the Sun when doing this, it would cause severe burning just like when looking directly at it.
But if the image of the Sun is greatly distorted by optical aberrations at oblique sight angles, its greater areal extension and its oblique projection on the retina will mean greater distribution of the intense light energy, resulting in less danger of retinal damage.

The eye's aberrations are so vast that it's more or less a miracle that we see so good that we actually do. It has been shown more than 200 years ago that the eye has a lateral astigmatism.

http://www.arkiv.certec.lth.se/dok/optikforsynsvaga/bilagor.pdf

http://www.telescope-optics.net/eye_aberrations.htm

Cheers!

//L

bh46118 said:

For some reason, I can't get a sharp image on the right side with any binocular without my glasses on. With them on, sharp as a tack. If I could be without the glasses, I would love to use the winged eye guards on all of my binos.

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Perhaps you have a little astigmatism in that eye?

bh46118 said:

If you have 20-20 vision, would you still get the same positive effect by using your binoculars with a pair of glasses in which the lenses haven't any prescription ? Does that make any sense ?

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I haven't read this whole thread, but I'm getting a little confused now. Surely any benefit of wearing glasses when using binoculars is only minor compared to the disadvantages?

Someone mentioned having some peripheral vision outside the magnified image. That could be achieved for non glasses wearers by using transparent eyecups, couldn't it, or "wireframe" eyecups? Maybe just drill some holes in them?

Advantages of not wearing glasses (which I do) include being able to centre the binoculars over your eyes accurately by feel, and having the eyecups out to block side light. I find that in some situations if I block the side light with one hand, the contrast of the image improves markedly.

pshute said:

I haven't read this whole thread,---

Someone mentioned having some peripheral vision outside the magnified image.

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That's largely what the thread subject is about.

pshute said:

That could be achieved for non glasses wearers by using transparent eyecups, couldn't it, or "wireframe" eyecups? Maybe just drill some holes in them?

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Strange! The very same thought occurred to me yesterday!

//L

I think inevitably this thread will have to confront the question of whether it's preferable to maximize the lateral light allowed to enter the eye for a sense of greater immersion or better to minimize the damage that bright lateral light can cause to the axial image by blocking it. I do see the perceived increase in apparent field being discussed here, but even so, I prefer to completely block lateral light with winged eyecups to improve contrast and shadow detail in the center of the field. This appears to be one of those cases where experienced observers can have exactly the opposite preferences.

It's obvious that this is very much an individual thing, as no one else sees through your eyes. My statements are based on what works for me. The technical things being discussed here are far beyond my understanding.

Bruce

pshute said:

I haven't read this whole thread, but I'm getting a little confused now. Surely any benefit of wearing glasses when using binoculars is only minor compared to the disadvantages?

Someone mentioned having some peripheral vision outside the magnified image. That could be achieved for non glasses wearers by using transparent eyecups, couldn't it, or "wireframe" eyecups? Maybe just drill some holes in them?

Advantages of not wearing glasses (which I do) include being able to centre the binoculars over your eyes accurately by feel, and having the eyecups out to block side light. I find that in some situations if I block the side light with one hand, the contrast of the image improves markedly.

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henry link said:

I think inevitably this thread will have to confront the question of whether it's preferable to maximize the lateral light allowed to enter the eye for a sense of greater immersion or better to minimize the damage that bright lateral light can cause to the axial image by blocking it. I do see the perceived increase in apparent field being discussed here, but even so, I prefer to completely block lateral light with winged eyecups to improve contrast and shadow detail in the center of the field. This appears to be one of those cases where experienced observers can have exactly the opposite preferences.

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Nice wrap-up of the discussion, Henry, and about as far as I would want to go with it. When I had perfect eyesight I certainly didn't seek out non-prescription glasses to improve the visual field, and probably wouldn't today (even if my future self said it would be a great idea). But now that I must use spectacles I'm grateful that advanced technology allows me to get amazing benefits from them. It's really kickstarted my birding.

On this thread Kimmo was the first to bring up transparent eyecups, which would introduce diffused side light but prevent side images. I'm confident he knew this would probably be a worst case.

Thanks for the stimulating thread, //LS, but my eyeballs are starting to melt. o

Ed

I don't know if any of these, in conjunction with a baseball cap, would work to block sunlight or not ? http://www.dctsa.com/shooting-blinders.html

Bruce

pshute said:

I haven't read this whole thread, but I'm getting a little confused now. Surely any benefit of wearing glasses when using binoculars is only minor compared to the disadvantages?

Someone mentioned having some peripheral vision outside the magnified image. That could be achieved for non glasses wearers by using transparent eyecups, couldn't it, or "wireframe" eyecups? Maybe just drill some holes in them?

Advantages of not wearing glasses (which I do) include being able to centre the binoculars over your eyes accurately by feel, and having the eyecups out to block side light. I find that in some situations if I block the side light with one hand, the contrast of the image improves markedly.

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Over ths last few days I have been using some vintage 7x35 porros. A couple of them I will likely always think of as the Looksharp Model 65 WA. What they are is two Tasco 400 Internationals. One has a fov of 11*, the other 11.5*. Neither has much eye relief. I can take the rubber eye cap off and by the skin of my eye lid I can barely see the field stop. This combination of wide fov and being to get the unaided eye right up to the ocular lens does a pretty good job of bring a real image to what Looksharp illustrated here. I think it helped me as a non eye glass wearer. I think the value is less for those with glasses.

However, I still prefer to block side light, even with the 77 and 80* afov's of these Tascos. While I better understand the thread, I have to say I tend to agree with Henry.

Steve C said:

Over ths last few days I have been using some vintage 7x35 porros. A couple of them I will likely always think of as the Looksharp Model 65 WA. What they are is two Tasco 400 Internationals. One has a fov of 11*, the other 11.5*. Neither has much eye relief. I can take the rubber eye cap off and by the skin of my eye lid I can barely see the field stop. This combination of wide fov and being to get the unaided eye right up to the ocular lens does a pretty good job of bring a real image to what Looksharp illustrated here. I think it helped me as a non eye glass wearer. I think the value is less for those with glasses.

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11° would be nice. I would think with glasses this would be back down to a normal FOV because of the short relief.

Then one has the problem that it's very difficult to tell if one has the eyepieces centred over one's eyes, so one ends up not looking through the sharpest part of the optics, getting blackouts, etc. It's difficult to even get the separation right if you can't see the field stops.

I wonder if it would be possible to use such binoculars with glasses if the circular field stops were replaced with a smaller suspended ring. I've attached what I think this might look like. Probably wrong as I've never looked through binicoulars with the field stop removed, so I don't know what irregular obstructions they normally hide.

I would imagine most binoculars could have a much wider FOV, but the manufacturer fits field stops designed to:
a) hide all obstructions
b) hide the outer parts of the view that don't meet their specifications for sharpness.

This thread seems to be largely about being able to see birds in your peripheral vision outside the magnified view while looking through binoculars, so it's probably not off topic to discuss a way of seeing more in the magnified view.

I'd be interested to know if people would mind having the field stops widened for a wider FOV if that meant the previously invisible parts weren't that sharp. The idea of the ring is to demarcate the part of the view that's sharp, and to allow glasses wearers to still be able to centre the lenses on their eyes. Anything you can see outside of the ring is a bonus, and serves to help find birds that would normally be hidden.

pshute said:

I wonder if it would be possible to use such binoculars with glasses if the circular field stops were replaced with a smaller suspended ring.

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An alternative to the ring is to take a normal circular field stop and hack some bits out, leaving enough of the original edge for the user to be able to tell where the circle of the field stop was. I think I'd prefer the ring, but this is probably a cheaper way to do it.

Any volunteers to open a pair up a cut some bits out of the field stops?

Those Tascos I referenced are not for either cold weather or for eye glass wearers. With glasses you can barely get close enough for the images to merge. Your eyes are so close to the ocular lens, that fogging is a real problem in cold weather. If you are a non eye glass wearer and can find one of these, then the perception of fov as described here is a lot easier to visualize.