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AFOV, focus speed and common beliefs (1 Viewer)

elkcub, not all eyeglasses magnify the image (finally projected on the retina), only convex lenses for hyperopes do. As for myself, I am myopic, about -1,50 D which gives a very minute minification. I think you and me are strongly affected by an optical illusion (see link below)
Trying my Vortex (high eyepoint 22 mm) with the eyecups collapsed, moving the bin back and forth within the range limited by 1) blackout/kidneybeaning and 2) eyecup vignetting, the FOV feels larger when the bin is moved away from the eyes.
Also, this is where the rims appear the thinnest, and consequently, the lateral visual field is least affected. You have the Zeiss Classic 7x42 and know what I mean.

Looksharp,

Sorry to take this long to respond, but I was out buying a car and I had a few false starts composing this.

Yes, I would certainly agree that you being myopic handily discounts an explanation based on spectacle magnification. Forgive me for being pedantic, however, but in the area of perceptual psychology illusions are formally misperceptions, which are to be distinguished from the underlying perceptual processes that explain them. We don't generally reverse the process and use illusions to explain underlying visual-perceptual processes. (There are one or two notable exceptions when the illusion can be quantified. For example, Hemholtz' checkerboard illusion was quantified successfully and then used as a parameter to explain the "Globe Effect," which is yet another illusion (see http://www.holgermerlitz.de/globe/distortion.html).

I would say the perceptual phenomenon we experience with eyeglasses and binoculars is simply a manifestation of "size constancy," which is an ongoing perceptual process. It is not an illusion because there are no misperceptions involved. Objects either appear larger or smaller. This can be easily simulated, incidentally, by looking through a short tube at, let's say, a picture hung on the wall 15-20 ft. away. (A toilet paper tube works.) When the tube is put in front of your eye the picture immediately seems to become smaller, yet the retinal image remains the same either way. This is not an illusion, but rather the operation of the perceptual process known as size constancy. The mechanics are that the tube blocks off peripheral visual cues that the brain needs to estimate object distance, and, hence, object size. Under such conditions size perception becomes limited to the cue of retinal image size.

What I've increasingly come to understand is that the constancy mechanism even applies when the scene is differentially magnified. As mentioned in my earlier post, peripheral cues are still useful. Putting what you said above into this framework, when the rim appears to be thinnest note that it also least occludes peripheral cues.

It took me a while to get past your statement that you and I "are strongly affected by an optical illusion," as if we were unique in the world. :-O

Actually, I believe that everyone experiences this perceptual effect. See below.

Ed
 

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It took me a while to get past your statement that you and I "are strongly affected by an optical illusion," as if we were unique in the world. :-O

Actually, I believe that everyone experiences this perceptual effect. See below.

Ed

Sorry Ed, it's just that you, me and Kevin seem to agree more on this user-specific aspect on binocular use, as opposed to more scientific approaches. It would be very nice if a mathematical formula could be used to quantify this perceived property of binoculars.
However, I suppose that will not happen. I am very convinced that you are on the right track talking about size constancy, though measuring it might not be as easy as in your attached picture.
But it would be sad if this effect was put aside as mumbo-jumbo only because of its built-in inmeasurability (English is not my mother-tounge, apparently)

But besides the major difference between scientific approaches and user-perspective, I strongly suspect that the degree or level of misperception is not equal between individuals.

AC/A ratio (accomodative convergence per accomodative power) has a lot impact on the perceived size of the retinal image. By putting prisms in front of the eyes, they will be forced to adjust their position in order to avoid double-vision. The extra-ocular muscles then send signals to the brain how their respective tension is, and the brain computes these signals with respect to the simultaneous accommodation, and finally there will be a perceived change in object size.
Anyone who goes to an optometrist can ask for a prism flipper test. Prisms with their base towards your nose will allow the eyes to converge less, and the perceived object (text) size will appear larger.
Prism with the base temporally will force the eyes to converge more than they would without them, and the perceived object size will appear smaller.

But, as I wrote, the level of change is not equal to all individuals. Some will see a small perceived size change, while others will see an immense change.
The AC/A ratio plays a certain role in this.

Thank you for sharing your knowledge, I will get back tomorrow to read even more thoroughly. Now it is 1:40 AM here and the bed cries out for me.
 
I also have to add that spectacle lenses do have a real (measurable) impact on the retinal image size. But simultaneously, as the spectacles induce changes in the eyeballs' convergence, the perceived image size also becomes modified either towards even greater - or lesser - magnification/minification.
Luckily, the healthy human brain is very prone to adapt to the new circumstances, and this is why spectacles really work. If it wasn't, we might not even be helped by contact lenses, even though their impact on perceived image size generally is less than spectacles'.
 
Sorry Ed, it's just that you, me and Kevin seem to agree more on this user-specific aspect on binocular use, as opposed to more scientific approaches. It would be very nice if a mathematical formula could be used to quantify this perceived property of binoculars.
However, I suppose that will not happen. I am very convinced that you are on the right track talking about size constancy, though measuring it might not be as easy as in your attached picture.
But it would be sad if this effect was put aside as mumbo-jumbo only because of its built-in inmeasurability (English is not my mother-tounge, apparently)

But besides the major difference between scientific approaches and user-perspective, I strongly suspect that the degree or level of misperception is not equal between individuals.

AC/A ratio (accomodative convergence per accomodative power) has a lot impact on the perceived size of the retinal image. By putting prisms in front of the eyes, they will be forced to adjust their position in order to avoid double-vision. The extra-ocular muscles then send signals to the brain how their respective tension is, and the brain computes these signals with respect to the simultaneous accommodation, and finally there will be a perceived change in object size.
Anyone who goes to an optometrist can ask for a prism flipper test. Prisms with their base towards your nose will allow the eyes to converge less, and the perceived object (text) size will appear larger.
Prism with the base temporally will force the eyes to converge more than they would without them, and the perceived object size will appear smaller.

But, as I wrote, the level of change is not equal to all individuals. Some will see a small perceived size change, while others will see an immense change.
The AC/A ratio plays a certain role in this.

Thank you for sharing your knowledge, I will get back tomorrow to read even more thoroughly. Now it is 1:40 AM here and the bed cries out for me.

Looksharp, you're doing great expressing ideas in English, and certainly have introduced several that I hadn't considered. Most people, I suspect, are not familiar or interested in oculomotor systems and perception, so much of this is probably Greek (or might as well be). ;)

I'm aware that prisms can be used to modify binocular convergence, but didn't know about changes in perceived image size. Of course it makes sense since size perception depends upon distance perception, and distance perception depends upon both accommodation and vergence cues. As a wild guess I would think the base-in prism effect is strongest for near targets, and that the observer probably adapts to it over time.

Are you by any chance an opthalmologist? I can't help but think about your Swedish countryman, the famous professor of opthalmology Allvar Gullstrand, who won the Nobel prize.
 
Are you by any chance an opthalmologist? I can't help but think about your Swedish countryman, the famous professor of opthalmology Allvar Gullstrand, who won the Nobel prize.

In my leisure I am a bird-watcher with a strong optics interest. But for a living I am an optometrist, so I perform visual examinations and fit contact lenses.
Here in Sweden, optometrists have no role in purely medical concerns, so when I meet a customer/patient that I suspect might have an eye disease, I forward them to an ophtalmologist.
So you could see me as optician/optometrist.

Kind regards

L
 
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