FOV and Blackout Axis (1 Viewer)

Not sure how to phrase this title, much less search for it.

I noticed something strange with my SF 42s. With the glass to my face and centered, I can point my eyes up or down and see to the edges. If I do the same left or right, I get blackouts. Basically not possible to directpy view the horizontal edges without moving my head, which is only bugging me because vertical permits it without even hinting at blacking out.. Someone school me on this?

This happens because the eyeball rotates in a different way horizontally compared to vertically. Horizontal rotation causes the eye's pupil to be displaced in the direction of the rotation considerably more than when the eyeball is rotated vertically, especially down. The result is increased off-axis vignetting of the exit pupil from horizontal movement and that causes the blackouts you see.

Beautiful. That was the only thing I could think might explain it but I couldn't imagine the eye having two different pivot points.

That said, seems like something worth engineering around when developing wide FOV systems, though it might not be possible to compensate for without significant horizontal distortion when viewing the center.

Whiterain said:

Beautiful. That was the only thing I could think might explain it but I couldn't imagine the eye having two different pivot points.

That said, seems like something worth engineering around when developing wide FOV systems, though it might not be possible to compensate for without significant horizontal distortion when viewing the center.

Click to expand...

WJC :cat:

I watched a few medical videos and looked at these types of images, but haven't seen anything supporting my thought or Henry's statement. Nothing, on its face, mentions different pivot points, the 4 primary muscles seem to be symmetrical and equally forward on the organ, and any stabilization of the circumference muscles should (or might) offer the same amount of positional stability.

Is the translational shift a function of the eye socket shape or simply muscle/ligature?

I confess I didn't get this idea from any medical source. I used an artificial star test to investigate how vignetting develops at different points along the field edge. It's pretty easy to do.

Start by making an artificial star. It can be a pinhole in foil stretched over a flashlight lens or a glitter point of the sun from a small shiny ball. It's size is not too critical for this purpose. It just needs to be bright enough so that it will be visible when viewed far out of focus.

Set the binocular focus to infinity and view the star at 3-4 meters. It should look like a blank gray disc, subtending about 5º of apparent field. The disc is a well focused image of either the exit pupil if it's smaller than the eye's pupil or the eye's pupil if that's smaller than the exit pupil. I would suggest capping one side of the binocular and using only one eye to simplify things. Move the disc from the center of the field to the edge at 3:00 and then to 6:00 taking care not to shift the position of the eyeball away from the direction of its rotation.

As the disc approaches the field edge it will be increasingly vignetted depending on size of the exit pupil relative to the eye's pupil, the amount of vignette allowed by the binocular's design and the position of the eye's pupil. The closer the eye's pupil is to the field edge being examined the more vignette will be seen until the exit pupil finally turns into a slit and disappears. I believe you'll see the exit pupil become a slit or completely disappear at about 3-5º of apparent field from the edge at 3:00, but the exit pupil might lose only about half its diameter at the same angular distance from the field edge 6:00. Moving your eye back and forth horizontally will cause the amount of vignette to increase and decrease at 3:00. Moving your eye up and down will have the same effect at 6:00.

BTW, this phenomenon first came up in a different discussion. People occasionally report better edge sharpness near the field edge of the the horizontal axis compared to the vertical axis. Most of the time that's not a binocular defect. It's caused by the very same difference in vertical and horizontal vignetting described above. The extra sharpness at 9:00 and 3:00 occurs when the vignetted exit pupil becomes so much smaller than the eye's pupil that it acts like a camera lens diaphragm went stopped down to a small aperture to create wide depth of field. In a binocular the effect is to bring objects near the field edge, normally unfocused by field curvature, within the enhanced DOF just before they are completely blocked from view by the vignetting.

Henry

Whiterain said:

Beautiful. That was the only thing I could think might explain it but I couldn't imagine the eye having two different pivot points.

That said, seems like something worth engineering around when developing wide FOV systems, though it might not be possible to compensate for without significant horizontal distortion when viewing the center.

Click to expand...

I suppose you have adjusted the IPD on the binoculars to reach the optimal level of viewing. I suspect that is what is going on.

Jerry

That was my first thought, but its a symmetrical phenomenon (inside and outside). Henry may be on to something, i imagining it as though the light coming in forms a circle, but that if you could isolate the horizontal light that it might not be as... much? Nope that still doesn't make any sense.

So... eye voodoo? Multiple pivot points is the only thing that adds up, be that through musculature or physical constraints. Most animals have a horizontally configured eye, probably some sort of overlap with that?

Whiterain said:

Not sure how to phrase this title, much less search for it.

I noticed something strange with my SF 42s. With the glass to my face and centered, I can point my eyes up or down and see to the edges. If I do the same left or right, I get blackouts. Basically not possible to direct[l]y view the horizontal edges without moving my head, which is only bugging me because vertical permits it without even hinting at blacking out.. Someone school me on this?

Click to expand...

Holding the binoculars front and center, when your eyes move vertically to view the upper or lower "edges" they remain symmetrical, which allows for normal binocular viewing. When the eyes move left or right to view lateral edges, they move asymmetrically, i.e., one points towards the nose (converges) and one towards the ear (diverges). If the edges are at an extreme peripheral angle the view must become monocular, i.e., the eye pointed at the nose becomes occluded. Hence, one perceives a 'blackout.'

Ed

Good, clear explanation, Ed! It is almost as if you have studied it!

Bob

ceasar said:

Good, clear explanation, Ed! It is almost as if you have studied it!

Bob

Click to expand...

...and it would make sense, except I first noticed it with one objective lens capped.

My common sense filter is yelling "your vision could not possibly be occluded by your nose when using binoculars, since the whole nose would be occluded by the eye cups, and would still be beyond any field of view afforded by binoculars if those eye cups weren't there."

Whiterain said:

...and it would make sense, except I first noticed it with one objective lens capped.
...

Click to expand...

... and then you said "...With the glass to my face and centered, I can point my eyes up or down and see to the edges.

Common sense tells me to question whatever it is you're talking about.

Ed

PS. Yes, I should have said: ...i.e., the eye pointed at the nose becomes occluded 'due to greater rotational vignetting.'

I can see how that could be misunderstood by those who can move one eye independently. I am not one of those people, and simply don't know how to express that more clearly.

Henry's explanation makes sense, but I'm probably just missing something there. Is the point that its just how all optics work, prisms work, just binos? Or how the eye works? If the lateral pupil shift is greater than the horizontal shift when the organ rotates the same amount, that implies a different (or dynamic) point of origin, no? Apologies if you already addressed it in that detailed post; probably a little over my head at the moment.

Whiterain,

Note that I clarified my comment in post #9. Nasal side occlusion is probably due to differential vignetting. In normal viewing the nose does get in the way.

When a binocular is "centered," its circular exit pupil is positioned on the eye's circular entry pupil. Think of them as flat parallel disks. If the binocular remains stationary, any rotation of the eyes will will make the two disks nonparallel. So the circle of light coming from the binoculars' exit pupil will no longer enter a circular hole into the eye, but rather an elliptical slot with a smaller area (i.e., a 'cat's eye). As eye rotation increases the slot becomes narrower and narrower until it becomes a st. line with no area for light to enter at all.

As the diagram demonstrates, the nasal eye rotates more to view the same lateral point as the temporal eye, which means that for lateral viewing there is differential vignetting. The nasal eye has more.

There are other possible complications too. As the eye rotates it also moves laterally which requires recentering to the optical axis. Further, the binoculars' design may produce "spherical aberration of the exit pupil" which induces "kidney bean" effects that you could be seeing.

Over and out.
Ed

PS. Vertical rotation produces equal vignetting to each eye.

henry link said:

I confess I didn't get this idea from any medical source. I used an artificial star test to investigate how vignetting develops at different points along the field edge. It's pretty easy to do.

Start by making an artificial star. It can be a pinhole in foil stretched over a flashlight lens or a glitter point of the sun from a small shiny ball. It's size is not too critical for this purpose. It just needs to be bright enough so that it will be visible when viewed far out of focus.

Set the binocular focus to infinity and view the star at 3-4 meters. It should look like a blank gray disc, subtending about 5º of apparent field. The disc is a well focused image of either the exit pupil if it's smaller than the eye's pupil or the eye's pupil if that's smaller than the exit pupil. I would suggest capping one side of the binocular and using only one eye to simplify things. Move the disc from the center of the field to the edge at 3:00 and then to 6:00 taking care not to shift the position of the eyeball away from the direction of its rotation.

As the disc approaches the field edge it will be increasingly vignetted depending on size of the exit pupil relative to the eye's pupil, the amount of vignette allowed by the binocular's design and the position of the eye's pupil. The closer the eye's pupil is to the field edge being examined the more vignette will be seen until the exit pupil finally turns into a slit and disappears. I believe you'll see the exit pupil become a slit or completely disappear at about 3-5º of apparent field from the edge at 3:00, but the exit pupil might lose only about half its diameter at the same angular distance from the field edge 6:00. Moving your eye back and forth horizontally will cause the amount of vignette to increase and decrease at 3:00. Moving your eye up and down will have the same effect at 6:00.

BTW, this phenomenon first came up in a different discussion. People occasionally report better edge sharpness near the field edge of the the horizontal axis compared to the vertical axis. Most of the time that's not a binocular defect. It's caused by the very same difference in vertical and horizontal vignetting described above. The extra sharpness at 9:00 and 3:00 occurs when the vignetted exit pupil becomes so much smaller than the eye's pupil that it acts like a camera lens diaphragm went stopped down to a small aperture to create wide depth of field. In a binocular the effect is to bring objects near the field edge, normally unfocused by field curvature, within the enhanced DOF just before they are completely blocked from view by the vignetting.

Henry

Click to expand...

Henry,

I did want to mention that your research into this aspect is very interesting. It never would have occurred to me, and it makes sense. :t:

Ed

elkcub said:

Nasal side occlusion is probably due to differential vignetting.

Click to expand...

Starting to make a bit more sense for me. I'm still missing how vignetting would be different between eyes in this case. If you were looking at something very close to your face and the eyes had to converge, this makes sense. Does it still work that way with binoculars? Doesn't sound like it should if d=infinity.

elkcub said:

As the diagram demonstrates, the nasal eye rotates more to view the same lateral point as the temporal eye, which means that for lateral viewing there is differential vignetting. The nasal eye has more.

Click to expand...

Seems that the eyes should be relatively parallel and in the case of looking to the extreme right edge of the field that each eye would require equal lateral rotation, right? Very possible I'm just missing how the diagram shows that, but it isn't exactly on a blinking neon sign if it does.

elkcub said:

There are other possible complications too. As the eye rotates it also moves laterally which requires recentering to the optical axis.

Click to expand...

This might be the heart of the matter. When the eye moves laterally, do you mean the pupil's relative position changes, or that the center of the eyeball has a translational shift?

I kept reading a bit and tried to search with different terms as they came up, eventually leading to paper called "Axis of Eye Rotation Changes with Head-Pitch Orientation during Head Impulses about Earth-Vertical" https://www.ncbi.nlm.nih.gov/pmc/ar...ubject changes,though Listing's plane has not

Interesting excerpt:
"Two paradigms provide evidence of a compromise between Listing's law and a perfectly compensatory VOR. First, when a subject changes gaze between an up to a down far target during a passive head rotation about Earth-vertical with the head upright in neutral position, the axis of eye rotation pitches backwards or forwards depending on the vertical position of the eye in the orbit, even though Listing's plane has not changed its orientation."

So I went back outside and tried again. Initially I noticed the pupil reaching the edges of the eyebox and got the vesica piscis shape as you mentioned in all directions. Predictable, but not what I had observed before...

Then tried again, and was unable to see (via direct view) ANY of the edges.

Finally I tried to account for vertical position and recreate what I was doing when I noticed it originally and was able to recreate it. Sounding like the answer might be a lot more nuanced and less interesting than I'd hoped, if this makes sense:

When I'd done it initially, I was in a chair, leaning forward to support my elbows with my knees, and gazing at something elevated a few degrees upward. The target height and orientation to the optics means I was already "looking up" about 20 degrees.

The nuanced part is that those different observations and their causes might be pretty freakin' irrelevant, since recreating any of this are more dependent on facial structure, nose shape, and the O.D. of the eye cups, since every one of those things is putting a bigger variable into the system than any minute change to the eye's coordinates.

You guys clearly have a better foundation for this stuff, so I'm curious if this adds up?

You guys clearly have a better foundation for this stuff, so I'm curious if this adds up?

Click to expand...

Sorry to say that I don't understand the initial observation you asked for help to explain. It would appear that even you had difficulty repeating whatever it was, but for some reason needed the answer to involve the esoterica about the location of eye rotation axes. The referenced study involved head movements as well as eye movements, which is well beyond the usual scope of binocular usage. So, to be truthful I'm not coming away with anything other than hearing about Henry's nifty observations.

On a positive note I would say that the discussion underscores a frustrating lack of research in this area of applied optics, namely the human interface dynamics of visual instruments. Some authors have come close but none have laid out a general framework, such as was done by Sheldon Ebenholtz in his classic book on "Oculomotor Systems and Perception." You might want to acquire that book, incidentally, since it discusses many related topics, and even the perceptual effects of vertical eye-position information.

Cheers,
Ed

elkcub said:

On a positive note I would say that the discussion underscores a frustrating lack of research in this area of applied optics, namely the human interface dynamics of visual instruments.

Cheers,
Ed

Click to expand...

Ed,

Thank you for your explanation of the asymmetry of eyes' rotations when viewing a peripheral object. Very interesting! I learned something new today from your comments and from Henry's star test (which implies that vignetted beams near the edges of FOV actually can help see the edges better as they increase the eye's DoF and this effect somewhat mitigates the defocus caused by field curvature). Thank you again, both Ed and Henry!!

I too have noticed "the frustrating lack of research" or any attention at all to the complicated problem of interfacing visual instruments to the human eye. There is a chapter in the book by Smith and Atchison (The Eye and Visual Optical Instruments) but I have not seen much beyond that. This is a serious and significant area that needs to be investigated. FYI, I am doing this very type of research myself, focusing primarily on visual ergonomics of riflescopes but I am looking into binoculars-human eye interface too.

Have a nice weekend,
-Omid

The phenomenon is consistent, but did require certain conditions to fully isolate it. Bit short sighted to be dismissive considering multiple pools of information doing everything except contradict it. Glad I asked, since I learned here and was driven to learn elsewhere. Fortunately it was my question and others' satisfaction about taking something away from it is a biproduct rather that a principal requirement, lest we all be disappointed with every click. Thanks everyone.