Perceived field of view (1 Viewer)

Binastro said:

Photographs are oblong.
T.V. and computer screens are oblong.

So why do we accept binocular fields that are round?
Why don't we demand oblong fields with binoculars?


B.

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Excellent question! Be patient and look up my name in USPTO's published patent application records in 2021..

-Omid

Each eyeball has more or less circular entrance pupil aperture, but visual perception is a brain process, constrained by but not overly determined by optics. I think of the retina as an extension of the brain rather than an input device. Past experience and expectation informs what is "seen."

My sense of my visual field without optical aid is that it is wider than it is tall (more azimuth less altitude). Also, my ability to converge an image in binoculars is much more sensitive to altitude miscollimation than Azimuth miscollimation. Though I haven't tested it in detail, I believe it is easier for most people to tolerate Azimuth miscollimation when the tubes are slightly crossed rather than slightly "de-crossed" (no idea of the right term).

My only point with this last bit about collimation is that our perception and perceptual preferences are more a matter of how our brain and various muscles have evolved. Prey animals tend to have different visual and attentional modes than predators

I have a hazy idea of what I think the OP is trying to get at, but struggle to properly articulate it. I noted the other weekend that when comparing my two favourite West German 8x30 porros the Binuxit had a greater "perceived field of view" than the Zeiss West. Stated field of view was identical (150m at 1000m) and this was borne out when checked against landmarks - but I could bring the Leitz a little closer to my eyes without experiencing blackouts, moving the field stop further outward. The Zeiss West had a little (only a little - but noticeable) more tunnel effect. Both of these are, of course, short eye relief designs - I have not yet tested a binocular with really long eye relief (say 20mm) without glasses but the eyecups of such binoculars probably need to be extended a fair bit to avoid blackouts when they are used without glasses, giving somewhat of a tunnel effect (less perceived field of view) even though the user is seeing the full field of view. When using an 8.5x42 SV (stated eye relief 20mm) with glasses I have to extend the eyecups about halfway to the first stop - this does not seem to decrease perceived field of view compared to binoculars with 14 to 15mm eye relief, but if I were using it without glasses I would have to extend the eyecups much further. I'll check this with my brother's unit at the earliest opportunity.

Sharpness all the way to the edge, to me, increases perceived field of view. Binoculars with field flatteners in some cases (eg. Swarovski SV series) have a field of view that is almost all sweet spot and can (at least in my perception) match larger fields of view with poorer edge sharpness.

Patudo said:

I have a hazy idea of what I think the OP is trying to get at, but struggle to properly articulate it.

......

Stated field of view was identical (150m at 1000m) and this was borne out when checked against landmarks - but I could bring the Leitz a little closer to my eyes without experiencing blackouts, moving the field stop further outward.

.........


Sharpness all the way to the edge, to me, increases perceived field of view. Binoculars with field flatteners in some cases (eg. Swarovski SV series) have a field of view that is almost all sweet spot and can (at least in my perception) match larger fields of view with poorer edge sharpness.

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Patudo,
You've articulated your experience relative to the matter at hand very well.
And your last point has not been made in this discussion (at least recently).

The aesthetic criticisms about flat field that I've read numerous times, do not make much sense to me. In general, I agree with the concept that our eyes tend to focus in the center of the field, so absolute sharpness to the edge isn't a necessity, but I am puzzled by the complaints about it. If it exacerbates rolling ball, that's a separate issue from the actual image itself.

-Bill

tenex said:

Do I have this about right, and can anyone offer further technical explanation? Or is it the case that high-ER designs actually wind up limiting the real FOV, and thus the apparent as well?

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Hi Tenex, I try to answer. As you know, the field of view is determined by the optical scheme of the eyepiece and its field diaphragm.
The visible field is generally chosen by the designer, also based on the distance of the pupil extracted from that optical scheme.
Some choices will be better or easier than others, as optical geometry allows it. For example, this is the case with old designs, but unsuitable for glasses.
The geometric rendering of the eyepiece is very responsible for the three-dimensional sensation (immersion in the scene, perceived distortion, crushing of the planes in the depth, etc.). And the new productions of short binoculars (with short focal length) with a wide and flattened field, require short eyepieces from which to obtain long pupillary extractions (more ideal for glasses).
This makes it difficult to draw good eyepieces, so many results deform the final geometries and degrade the three-dimensional rendering.
The new Swarovski EL are examples of reference as regards the wide flattened field, without distortion and sharp to the edge, which maintains a good three-dimensional geometry. With the only defect of producing the globe effect.

A curved field will always be narrower than the same flat field.
And this is not why the trigonometric formula used in optical physics and therefore also in ISO standards, delivers a "slightly lower" value. Trigonometry is a mathematical function that does not produce errors: 2 + 2 = 4 always and in any case, regardless of the mentality or personal opinion of some people.

The field diaphragm of the eyepiece determines and borders what can be seen in the binoculars. If I can see a 140m field (420ft / 1000yd or 8 °), I will see 140m field from a distance of 1'000m, regardless of distortion, curvature, astigmatism or any other useless inference.
The edges of the observation window of that binoculars are drawn by the field diaphragm and the window will have an apparent amplitude calculable only with the trigonometric formula (ISO).
Thus, 140m in binoculars 10x = 70 °, while 140m in 8x = 58 °, etc.

The improper gesture of multiplying the amplitude of the angular field by the magnification is a completely incorrect procedure that only leads to incorrect results (even a lot).

What you need to measure is the width of the observation window that you see inside your binoculars and compare it with what you see with the naked eye. Place the binoculars on a tripod at a distance of 10cm (4 ") from the wall, so that the optical axis is orthogonal. Now, with your right eye look inside the left eyepiece and with your left eye check the wall size of the binoculars window, marking the vertical dimension (the diameter). Then measure the precise distance between the wall and the pupil extracted from the eyepiece and do the trigonometric calculation, with the values ​​of the diameter and the distance. The result you get is that real of your instrument and that you can compare with other binoculars.
If you don't know how to do the calculation, give me the measurements you found, which I will calculate for you.

tenex said:

I'm interested in here is simply the width of the PFOV ("perceived field of view"), although I can't think of a way to measure it directly.

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That amplitude should only be measured in direct comparison to naked eye vision.
This is the only correct method.
Since the naked eye is the absolute reference as regards the geometry of the binoculars (magnification, field curvature, amplitude of the observation window, etc.) and of all optical observation instruments (telescopes, microscopes, telescopes, magnifying glasses, etc.).

henry link said:

The answer is "no". Moving the eye closer or farther from the back of the eyepiece does nothing to the true AFOV any more than it changes the size of objects within the AFOV. It seems to me that what you call a higher PFOV means replacing the blackness outside the eyepiece field stop with some sort of of lateral light, however unrelated it may be to the image within the field, something like the way TV news stations add blurry borders outside vertical cell phone videos just to fill the horizontal screen.

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My Zeiss SF has this light beyond the field stop. Some dislike it but I think it ads something to the view. Makes it seem even wider and brighter with that little glow beyond the field stop. like with some televisions that have the lights on the sides that reflect off the wall that change colors to match what’s on the screen.

Chosun Juan said:

When I say that I find the view more immersive without glasses on, this means that I back the eye cups out, and yet if I position my eye at the correct distance I get no increase in the black surround - ie. the Fov takes up the entire view. The extra feeling of immersion (provided it is a good sharp 66°+ AFov) comes from not having the side glare from behind my glasses from side light, and a greater degree of alignment margin of error making for an easier view.

Chosun :gh:

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I generally keep my glasses on as all my binoculars have long ER, but forced myself to take them off this weekend with my 8.5x42 SVs. I was pleased to find a more immersive view. On closely checking (one eye with glasses, one eye without) the apparent field of view was noticeably bigger with glasses off. I'm short sighted and my glasses seem to reduce the magnification a bit throwing the image a bit ahead of me and creating more tunnel view. I'm probably getting 8x instead in 8.5x with glasses on.

I'll be taking my glasses off more in future because I always felt the AFOV of the 8.5x42 SV was lacking a touch for my taste, but taking my glasses off seems to address that.

Robert Moore said:

My Zeiss SF has this light beyond the field stop. Some dislike it but I think it ads something to the view. Makes it seem even wider and brighter with that little glow beyond the field stop. like with some televisions that have the lights on the sides that reflect off the wall that change colors to match what’s on the screen.

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Hi Robert,

I think we may not be talking about the same thing.

Most binoculars show a circular FOV surrounded by a dark ring. The width of the dark ring varies for several reasons, but outside that ring an observer can also usually see the periphery of his own approximately 180º FOV. That large peripheral area of light is what I meant. If you see light within the dark ring just outside of the eyepiece fieldstop that would be caused by one of two things, neither IMO desirable. Firstly, it could be light from behind you coming around the side of your face and reflecting into your eye from the glass of the eyepiece or the area next to it, something that becomes more likely with a large diameter eyelens like the one on the SF. Secondly, it could be caused by light from the objective lens glancing off poorly baffled or blackened surfaces within the eyepiece. Unlike poorly baffled internal surfaces in front of the eyepiece fieldstop, which cause glare within the FOV, poor baffling or blackening inside the eyepiece causes glare in the dark area just outside the FOV.

My guess is that it's probably the first possibility in the case of the SF. That can be tested by simply blocking the light from behind you from reaching the eyelens when you notice the "glow" outside the fieldstop. If the light disappears then that's the problem and it could be fixed by face hugging winged eyecups. If it remains then it's light from the objective lens and you're stuck with it.

Henry

Robert Moore said:

My Zeiss SF has this light beyond the field stop. Some dislike it but I think it ads something to the view. Makes it seem even wider and brighter with that little glow beyond the field stop. like with some televisions that have the lights on the sides that reflect off the wall that change colors to match what’s on the screen.

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I observed the same thing with the two new Zeiss 8x42 SF's that I purchased. The light beyond the field stop was crescent shaped and orange in color. It bothered me so much I returned them. When you try Henry's test in post #29 let me know what you find. If the problem can be solved with winged eye cups I might try the Zeiss SF again. Thanks.

Allbinos mentioned it in their review of the Zeiss SF. "If not for strange slip-up with reflections beyond the eyepiece's diaphragm, most likely caused by a shiny ring inside tubes which aren’t baffled properly by apertures, you would get an instrument optically perfect, an ideal."

In the two SF samples I had in my possession, that crescent shaped light (white/blue) near the field stop was observed by me, with no light coming in from behind me or approaching 90 degrees to the objective. I felt that perhaps in the binocular design, to save length of the instrument, adequate baffling was sacrificed. Nice glass without it, but it just did not work for me. If they do another iteration of this glass, I will of course try them again myself.

Andy W.

dries1 said:

In the two SF samples I had in my possession, that crescent shaped light (white/blue) near the field stop was observed by me...

Andy W.

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By "near the fieldstop" do you mean outside the fieldstop in the black or inside the fieldstop within the FOV?

Henry,

Within the of the field of view at the periphery approaching the field stop.

Andy W.

Andy,

OK, that would be our old friend "veiling glare" coming from an internal reflection ahead of the eyepiece fieldstop. The usual culprits are the objective lens cell or the focusing lens cell or the front prism aperture or some combination of the three.

Henry

Henry,

I have never had this problem with any of the 5 FLs I own. I wonder if the internal baffling could have been improved, and there seems to be hardly any sufficient baffling outside the lens within the tubes.

Andy W.

dries1 said:

Henry,

I have never had this problem with any of the 5 FLs I own. I wonder if the internal baffling could have been improved, and there seems to be hardly any sufficient baffling outside the lens within the tubes.

Andy W.

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The objective and focusing lenses in the SF are completely different to the FL. The 42mm HT objectives and focusing lenses are identical to the FLs except for a little better baffling of the objective cell. If by "outside the lens within the tube" you mean baffling of the outside area in front of the objective lens that's not as effective as baffling internally just behind the objective cell.

You can never predict veiling glare from what you see when you look into the objectives. The internal surfaces that cause the problem will look just fine from the front since they reflect non image forming light back toward the eyepiece, not forward so you can see it from the front.

I doubt that the "glow beyond the fieldstop" Robert described would be related what you saw. Even if a binocular is perfectly baffled ahead of the fieldstop it could still have unbaffled reflections within the eyepiece, which will always appear outside the fieldstop.

Henry

Thanks Henry for the clarification. By the way the Astroluxe is so much easier to view with after I took off the rubber eye-cups from the plastic retainer which was warm on my face under cold conditions. The FOV opened up nicely.

Andy W.

The reflections past the field stop on my Zeiss is not from reflections behind the eyepieces. I just tested it. So something internally not baffled right or something to that nature. When I first looked through it it bothered me but now I’m used to it and I like everything else about the binocular so I don’t let it bother me anymore. I am always focused on the center view anyway

Leica bins in my opinion have the best looking field stops. Really pitch black beyond the stops. They know how to baffle.

Robert Moore said:

The reflections past the field stop on my Zeiss is not from reflections behind the eyepieces. I just tested it. So something internally not baffled right or something to that nature. When I first looked through it it bothered me but now I’m used to it and I like everything else about the binocular so I don’t let it bother me anymore. I am always focused on the center view anyway

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If you can't fix it getting used to it is the next best thing.