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PFOV concept (1 Viewer)

Renze,

I agree that transparency is not the perfect choice of words. But that's what I read in a review of the Meostar, the reviewer used that word to describe how the binoculars nearly seemed to disappear when held in front of the eyes.

Ed,

I believe you agree that the physical shape of the binoculars has an impact on how much of the visual field they obscure.
As I have tried to show, my hands must be in the equation because at least the right hand intrudes. It has to be right there in real use.
Admittedly, some binoculars permit a better grip like you described, but I doubt that could be done with the stubby Zeiss. Although slightly harder to quantify, it should be mentioned for binoculars like these that the hand may obscure the visual field to some degree. For others, that would be needless and thus easier to assess how the binocular itself promotes or obstructs the PFOV experience.
 
Assessing visual fields exactly without using a perimeter is nearly impossible. Doing it with a binocular in front of your eyes might be the recipe for epic fail.
Anyway, I've used a visual field map to make a rough estimation what happens in the visual field in exactly that situation.
The center part is the image, and it has an AFOV of about 60 degrees. Then comes the rim, which in this context must be of utmost importance. The size of the AFOV decides how far from center the fieldstop/inner edge of the black rim sits. The width of the rim decides how much of the periphery that can be seen.

The colored lines follow the visual field's lateral edges and are only there to enhance the readability of the map.
The black stripes indicate where the binocular intrudes into the visual field's medial parts so that the normal stereoscopic vision is lost. I've also marked where the image of the focusing knob is situated in the visual field. (the right one is for the left eye and vice versa).

This coarse map should correspond to #II or #IV of my drawings above but from the user's aspect. It is true that those drawings don't take stereo vision into account, but the visual field map should show that the superior (upper) and lateral (outer) parts of the visual field are the only of real interest here.

It shows we can divide PFOV into two subcategories:

1) The angular size of the AFOV in relation to the obscuration caused by the black rim.
Probably, a wide rim will not be as annoying if the AFOV is great as when AFOV is narrow.
2) The presence of peripheral visual impressions.
The distance needed to produce an unobstructed image (the eye relief) is important here, where a greater eye relief allows more peripheral vision.
Physical shape of the binoculars, eyecup features, hand placement et cetera may also contribute.
 

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...
This coarse map should correspond to #II or #IV of my drawings above but from the user's aspect. It is true that those drawings don't take stereo vision into account, but the visual field map should show that the superior (upper) and lateral (outer) parts of the visual field are the only of real interest here.

It shows we can divide PFOV into two subcategories:

1) The angular size of the AFOV in relation to the obscuration caused by the black rim.
Probably, a wide rim will not be as annoying if the AFOV is great as when AFOV is narrow.
2) The presence of peripheral visual impressions.
The distance needed to produce an unobstructed image (the eye relief) is important here, where a greater eye relief allows more peripheral vision.
Physical shape of the binoculars, eyecup features, hand placement et cetera may also contribute.

LS65,

Very nice! A portion of the focus wheel does lie within the field of vision of each eye, and placed more or less where you describe it. One has only to wink alternately to see it. But, like the nose, the obscuration disappears using both eyes, and probably for the same reason: the brain.

Your physical division of the PFOV summarizes our discussion nicely. A rim of any width probably is less annoying as AFOV increases.

Ed
 

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Dear fellows,

Please allow me to throw some history into the works.

In the 1950's the German optics-company Möller-Wedel (still in existence but not manufacturing binoculars any more) marketed a high quality - and expensive - reverse porro binocular, which was unusual in several aspects. Build quality was exceptional, the configuration out of the ordinary (8x32) and sitting in the locking set-screw holding the ocular arms was a kind of stem that screwed up or down allowing the user to rest it against the forehead for stability. I've owned this model and it worked. I don't think Möller-Wedel applied this feature for PFoV's sake (the eye relief was still rather small) but probably as a service to spectacles wearers in fear of scratching their glasses (rubber eyecups were not in vogue yet). See the picture.
Then there's an invention I've seen on Ross binoculars, based on the same idea but now using a rubber stem in fixed position (not adjustable but possibly allowing the user to put them on or off). As it happens there's an example listed on eBay UK right now (item number 320830154906). Note that this binocular is advertized as a Ross 8x35 Spectacle Solaross.
As I suspect the seller won't object to using his pics here, I'll include them for convenience.

Let me have your thoughts please.

Renze
 

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Renze,

strange you should bring these pictures up here. It was only yesterday the thought of a forehead rest like that came to my mind!

The eye relief of the Fury is large and if I want to take advantage of its glorious PFOV when I'm not wearing glasses, I'd need such support.

//L
 
Oh, coincidence is happening all the time.

I once made a support by screwing a deep rubber ring onto the IPD scale of a Zeiss 10x50 porro. The idea was to come free of the uncomfortable hard plastic eyecups while yet maintaining some stability. Because of the Zeiss' short eye relief I only needed some millimeters in the support, while in your case you'll need considerably more.
I have to say though that I didn't use 'the invention' for long, as a one-point support simply wasn't stable enough to me. Instead I sold the Zeiss.

Renze

PS. please note my custom made soft eyecups in picture 2. You can do anything with bicycle inner tubes.
 

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Like I wrote in the other post, the PFOV needs to be divided into two different parts. These are the AFOV and the black rim (annulus) surrounding the image, and the obscuration of the peripheral vision.


This series of pictures are intended to show how the light seen after passing through the binoculars changes depending on the distance to the oculars.
The first five oculars are identical in size, while the sixth is slightly larger.
More on that later.

It could be argued that the images don't take into account that the image of the ocular occupies an increasingly larger part of the retina when you get closer to it.
This also means that the closer to the oculars you come, the further out in the periphery the image of annulus will be located. This occurs exponentially, because of two reasons:
1) An object that comes closer by half the distance will occupy four times larger retinal space
2) The bulb shape of the eye. The further towards the edge of the visual field the image of an object is projected, the faster does it move towards the edge because of the steep angle.
Compare with how shadow's length increases faster and faster when sunset comes.

The outer, grey circle is of course the ocular's outer parts. The blue circle is the ocular lens. The white dot is the image through the bins.

The first picture just shows the exit pupil. If you find an object to look at, it will be equally enlarged to when the binoculars are close to the eyes but of course with an extremely narrow FOV.

In the second picture, the exit pupil is enlarged and too close to the eye to show sharp edges. Same with the third picture, where the "image" is just slightly smaller than the ocular lens.

The fourth picture shows the situation when the image seemingly is larger than the ocular lens, but you're not close enough to see the field stop.
You're still out of the eye relief.

The fifth picture show what I'd call an ideal situation. The annulus is very thin compared to the AFOV and obscures very little of what's in the periphery.

To show my point, I needed to make the sixth image larger than the others despite the uniform size of the five previous ones.
Since the full AFOV is seen even at a longer distance (like in #5) , it cannot be increased by getting closer with the eyes.
Instead, the width of the annulus increases, thus obscuring the peripheral visual impressions more than in #5.

The annulus does not entirely correspond to the physical width of the rim outside the ocular lens:
The inner part of the annulus in #5 and #6 are black, to indicate it's a part of the internal blackening of the bin.
Then comes the (grey) rim outside of it. I call the combined effect of the inner and outer part of the annulus the compound annulus.
The last image shows how blackout can look, when you're too close to the ocular.

With the Fury, the recession of the ocular lens does have some impact on the effect of reduced PFOV in #6 because it's at least 5-6 mm. Pushing the eyes all the way in will of course cause immense blackouts, but there's some room to find the difference between ideal distance and the reduced PFOV coming with closer distance.

Strangely, a very similar effect can be seen with the Zeiss FL, although the ocular lens recession is less than 2 mm - even this binocular has an ideal distance between the eye and the ocular lens where the compound annulus is very thin, and the "corridor" of decreasing PFOV before blackouts come.
The AFOV is panoramic and the eye relief is well harmonized with respect to use with or without spectacles.

/looksharp
 

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FrankD,

now I've tried to find the differences between the two oculars you've pictured.
From what I can see, the better has a less recessed ocular lens, bigger diameter ocular(?), more open periphery where the rim has a steeper angle.
The ocular lens also looks larger compared to the rim than the other's.

There may be internal differences how the oculars are constructed concerning eye relief and other things as well. If they are optically identical, I'm pretty sure this is a matter of peripheral vision differences caused by the the external differences of the bins.
 
LS,

I do like the fact that you are so fascinated with this subject. It has caused me to rethink the issue a bit.

Still, I am left feeling a bit of confusion. It may be that this is just an issue that many of us take for granted or it may be that I am oversimplifying it. Let me try to explain.

Looking at the last series of images you posted I am left with a few thoughts. When I first saw the images and didn't read through your post I thought I was seeing the progression of moving your eye closer to the ocular lens for any given binocular.

So, picture 1 would be an example of what the ocular would look like if I was holding the binocular out in front of me a good 6-10 inches.

Picture 2 looks the same if I had a different binocular but with a larger exit pupil, or if I was holding the original binocular a little bit closer than Picture 1 but not to the point where I was actually holding it up to my eyes for regular use.

Picture 3 just seems to be a little bit closer than Picture 2 but still not close enough for regular use.

Picture 4 looks like a binocular held up to my eyes with a narrow apparent field of view.

Picture 5 looks like a binocular held up to my eyes with a larger apparent field of view.

Picture 6 looks like a binocular with the same true field of view as picture 5 but a narrower apparent field of view because of magnification. An example would be an 8x42 versus a 7x42 both with a 420 foot field of view.

I took some handheld pics via my cell phone and a binocular I have on hand at the moment. I will put a little caption above each so you can see what I am trying to relate.
 
Picture one is a 6 mm exit pupil of a binocular held away from my eyes by a good 8-10 inches.
 

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Picture 4 is, again, about half the distance. Now we are at a point where it would apply to some binoculars that have short eye relief and I cannot get my eye close enough to the ocular lens to see the full field of view.
 

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Picture 5 is what you would see if your eye was at a position to see the full field of view without any black outs. I would call this the "ideal position" for your face and for the binocular. The pic itself isn't the best to represent this because of the limitations of the camera on the phone and because of my using a handheld method to take the picture. For the sake of discussion ignore the fuzziness of the field stop on the one edge.
 

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Picture 6 is what I would call a "blackout scenario". This is where the binocular has "too much" eye relief with the eyecups fully collapsed. The image shrinks in size and is similar, but not the same, to what would happen if you had the binocular too far away from your eye to see the full field of view. It is similar to Picture 4 in this regard. The difference is that the field stop edges are even fuzzier and eye placement is much more critical. In the Picture 4 scenario you can move your eye around the image some. In Picture 6 if you move your eye around the image then you get blackouts.

To correct the issue in Picture 6 you simply need to twist up the eyecup to the proper level in order to obtain an image represented in Picture 5.
 

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LS,
When I first saw the images and didn't read through your post I thought I was seeing the progression of moving your eye closer to the ocular lens for any given binocular.

And that is what I intended it to be. Basically, your pictures seem to show the same progression. Like I wrote, one could argue that I don't show the ocular larger when it's closer to the eye.
Pic #2 of mine is not a bin with a larger exit pupil, and you can see the fuzzy edges as as opposed to the sharp edges of a well-defined exit pupil. This is fairly close to the ocular, but way behind the eye relief.
Same with my picture #3. Both yours and mine picture #4 show when the image is larger than the ocular lens. You're still behind the maximum eye relief.

But your #6 does not correspond to mine. I do know what blackout/kidney beaning is and I have posted a photo in another thread to show that.
No, the field stop is very sharp in my #6 just as I intended it to be.
But the eye is closer still, just before blackouts occur.
The image has the same size while the annulus occupies a bigger portion of the visual field, thus decreasing the PFOV.
Pic #7 shows the blackout effect.

//L
 
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LS,

I see what you are saying in reference to your last comment. Assuming an individual can actually see the full field of view of a given model then a binocular with a larger apparent field of view (smaller annulus to use your term) gives the impression of a larger perceived field of view.
 
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