Two Mechanisms of Vision: Ambient Vision and Focal Vision (1 Viewer)

[Holger Merlitz]

Enlarging visual angles to create "a magnified object" vs enlarging visual angles to create "a magnified space"

The most basic way to describe binoculars effect on vision is by considering their magnification factor M. This means, binoculars increase visual angles subtended by "an object" by a factor of M.

If we assume M=10 and the object is a small bird sitting alone on a tree branch 10 meters away, the visual experience of seeing said bird via a10X telescope could be described in several ways:

• It appears that the bird remains at the same location, but its size is magnified (it looks like a large bird).
• It appears that the bird has come closer (as if the bird is sitting on a branch only 1m away from the observer).
• It appears that the observer has moved forward (as if he is looking at the bird from a point of view (PoV) 9m ahead of his actual location).

Which one of these scenarios do you think is more representative of our visual perception?

Now another experiment:

Imagine you have a polaroid SLR camera which takes nice color pictures and prints them out instantaneously. You go to Venice, Italy and stay at the center of Piazza San Marco with your camera. Then you take a series of pictures each in a direction slightly to the left of the previous picture. You carefully adjust your rotation angle so that your pictures show a continuous 360-degree field of view once stitched together in a panoramic display.

You bring all the pictures home and paste them around the inner wall of a circular tent of suitable radius which you have set up in your backyard. If the radius of the tent is correct, your pictures will cover the entire 360 degree of the inner wall, and you'll get a panoramic view of Piazza San Marco if you stand at the center of the tent and turn your head around.

During your next year, you decide to do something more impressive: you use a 10X telephoto lens on the same camera and take a sufficient number of photos to cover 360 degrees. You bring all the magnified images home and paste them around the inner walls of a suitably sized tent to create a 360-degree "magnified display" of Piazza San Marco. You stand at the center of the tent as before and look around.

What do you think you will see? Will you see a "magnified panorama" of Piazza San Marco?!! Can you see the details of paintings on the facade of the St Mark's Basilica now?

If the bird were moved closer, or equivalently the observer moved closer to the bird, then its perspective would be affected. This is not the case through a magnifying instrument: The perspective remains exactly the one produced at 10m distance, yet the bird would appear 10x larger. Along with the resulting perspective distortions, the extent in depth of the bird now appears unnaturally reduced - the object looks kind of squeezed. This is a well known effect when using strong telephoto lenses.

Regarding the panoramic poster: If its circumference increases by a factor 10, then so does its radius (or distance to the observer), so the observer would perceive no difference in detail.

Cheers,
Holger

 

[Omid]

I’m not sure how I would distinguish between having the bird move closer to me, and my moving closer to the bird.

That’s almost Einstinian.

Yes, based on pure geometry, and in the absence of additional perspective clues, there is no way to distinguish between any of the three scenarios. There could be an infinite combination of lone bird distances and lone bird sizes that are consistent with the apparent visual angle.

Despite the above geometric/optical ambiguity, most humans who have looked at birds and other natural objects through binoculars might say that one of the two latter scenarios are more representative of their perceptual experience. This is to say, telescopes appear to bring the object closer to the observer (Scenario 2) or, nearly equivalently, bring the observer's PoV closer to the object (Scenario 3). Rarely we perceive a giant bird or squirrel when we look at these animals through our binoculars (Scenario 1 is out).

Now, is there a way that an observer can distinguish between Scenarios 2 and 3? The answer is no if {the observer + his binoculars} remain stationary in space. But as soon as the observer moves around or rotates his PoV new geometrical constraints (in J. J. Gibson's terminology new invariants of space) will become available and we might be able to pick one scenario over the other. That's why I followed my bird questions with the thought experiment of creating a panoramic display of Piazza San Marco. Did you solve that? Can you see how making a 10X enlarged panoramic display bears on your question "how to distinguish between having the bird move closer to me, and my moving closer to the bird?"?

Cheers
-Omid

 

[Maljunulo]

That's why I followed my bird questions with the thought experiment of creating a panoramic display of Piazza San Marco. Did you solve that? Can you see how making a 10X enlarged panoramic display bears on your question "how to distinguish between having the bird move closer to me, and my moving closer to the bird?"?

Cheers
-Omid

No to both questions.

I am much too simple-minded for such pursuits.

Sorry.

 

[Omid]

If the bird were moved closer, or equivalently the observer moved closer to the bird, then its perspective would be affected. This is not the case through a magnifying instrument: The perspective remains exactly the one produced at 10m distance, yet the bird would appear 10x larger. Along with the resulting perspective distortions, the extent in depth of the bird now appears unnaturally reduced - the object looks kind of squeezed. This is a well known effect when using strong telephoto lenses.

Regarding the panoramic poster: If its circumference increases by a factor 10, then so does its radius (or distance to the observer), so the observer would perceive no difference in detail.

Cheers,
Holger

Hi Holger,

Yes, of course! If we take perspective into account, then "observer moving closer" and "object coming closer" can be distinguished from each other and, further, from the "Allice in Wonderland" perspective that optical zoom creates. In the case of observer movement, the visual angle of background objects (far buildings, mountains) will remain the same whereas in using optical zoom everything is magnified creating the perspective compression effect (aka telephoto effect) you mentioned. This music video shows perspective effect of natural observer movement in a beautiful manner:

What I had in mind was a simpler scenario without perspective (e.g. a lone bird on a tree branch or looking at a frontal church wall). It is interesting that even with perspective present, we seldom perceive optical magnification as a change in object size. We usually perceive it as "we have moved closer". In cinematography, a zoom lens is considered a cheap low-class alternative for actual camera movement (which requires setting up rails and other stabilizing equipment to move the camera closer to a scene). During the initial years of cinema, prominent directors hated zoom and never used it in their films. Zoom was only used in television news programs.

By antagonistic combination of zoom and camera movement, it is possible to keep the subject appear constant while the "space" he is in expands:

My "magnified panorama" experiment (which you unsewered correctly) reveals another striking fact: It is impossible to create a magnified (or minified) 360-degree visual space. No matter what lens focal length or field of view or film size we use to observe/measure/record/perceive the space around us, the resulting 360-degree visual world will have to shrink back into "true world" in which the horizontal visual angle between any two objects remains invariant. I think this very phenomenon is used by our Ambient Vision to calibrate itself: No matter what lens focal length is put on the eye (or correcting glass), it can calibrate the retinal image size to correspond to the "true" visual angle over the course of few hours or a few days. This is also how our biological visual system can deal with nonuniformity in the retinal cone/rod density and the change in the physical size of the eye during growth. {This is a deep topic that we can explore more fully later}.

Now, back to rotating PoVs: What happens if our tourist uses a pair of 10X binoculars and slowly turns around while standing in the middle of Piazza San Marco? What kind of natural (naked eye) visual experience will be analogues to his visual experience?

-Omid

 

[Jinac]

I imagine that it will be the same as if we put him on a giant turnstile with the center in the center of the Piazza and the radius 90% of the Piazza radius, so the tourist will turn ten times closer to the edges of the square.

 

[Omid]

I imagine that it will be the same as if we put him on a giant turnstile with the center in the center of the Piazza and the radius 90% of the Piazza radius, so the tourist will turn ten times closer to the edges of the square.

You nailed it! The visual effect of panning with binoculars is analogues to looking at the surrounding environment while sitting on a giant merry go round facing outwards That's why you should never pan with your binoculars. The unusual optical flow in the peripheral part of field of view caused by combination of translational and rotational apparent motion will cause dizziness and headache.

 

[Canip]

That's why you should never pan with your binoculars.

How do you follow a bird in flight with binoculars if you shouldn‘t pan?

 

[Thotmosis]

How do you follow a bird in flight with binoculars if you shouldn‘t pan?

It’s very simple: just close your eyes while panning

 

[Jinac]

The term "never" is rarely a good friend I think ^^
"Some people could feel headaches or dizziness" is maybe more true.

 

[Holger Merlitz]

You nailed it! The visual effect of panning with binoculars is analogues to looking at the surrounding environment while sitting on a giant merry go round facing outwards That's why you should never pan with your binoculars. The unusual optical flow in the peripheral part of field of view caused by combination of translational and rotational apparent motion will cause dizziness and headache.

At this point we should not overlook an important detail presented by Jinac: "I imagine that it will be the same as if we put him on a giant turnstile with the center in the center of the Piazza and the radius 90% of the Piazza radius, so the tourist will turn ten times closer to the edges of the square."

Indeed, the observer has now moved rather close to the motif, and thus the curvature of the angular space is now reduced by a factor of 10. To the observer it now appears as if a practically flat image were moving in front of her eyes. If you run the math, you may find that the velocities of the image points differ between center and edge of field by no more than half a percent or so, which is no longer detectable. All image points in the virtual image thus move at practically equal velocities through the field, as if you were walking along a huge flat poster.

Therefore, as such there is no problem with panning a binocular. As long as there is no distortion involved, that is. Many binoculars feature a distortion which may easily change the velocities of the image points by 5-10%, and sometimes in a nasty way, as is the case with mustache distortion. Since 2009 we further know that human vision can feature a distortion, too. It differs between individual persons, but most people seem to have a slight barrel distortion, which in average would alter velocities of image points by about 5% in such a panning binocular. This is indeed visible and can generate the globe effect. Luckily, instrumental distortion can be adjusted such that it helps compensating the visual distortion of an average observer, as it is done with the Zeiss SFL.

Cheers,
Holger

 

[Omid]

How do you follow a bird in flight with binoculars if you shouldn‘t pan?

Excellent question! I actually mentioned this very case in my post originally, but I deleted it later because I felt this topic requires a whole separate chapter in our discussion. I used the word panning as it is used in cinema and photography. In cinematography, "panning" refers to a horizontal camera movement where the camera pivots left or right from a fixed position, mimicking the action of turning your head to take in a wider view, similar to a "panorama".

If you are tracking a bird in flight, we could call it a "tracking movement" to emphasize that we are focusing on a single object with the intent to keep its image on the fovea. In ophthalmology and vision science, this is called a smooth pursuit eye movement to distinguish it from a fast saccadic movement. There are only two situations in which human eyes make a smooth scan-like movement and both situations require a specific "fixation target".

In a future post I will discuss the implications of making a tracking movement using binoculars. So far, I don't see any particular reason that this should cause visual discomfort.

The term "never" is rarely a good friend I think ^^
"Some people could feel headaches or dizziness" is maybe more true.

With panning defined as above (scanning a large scene with your binoculars to find a bird or just to enjoy the view), I stand with what I said. In fact, I will repeat it here again for additional emphasis: Never pan your binoculars. For a more detailed explanation, please wait until I respond to Dr. Merlitz's comments in Post #30.

Thank you both Jinac and Canip for following my posts and contributing to this thread

 

[Maljunulo]

I find the constant references to photography in this forum tiring.

We are talking about binoculars, eyeballs, and brains, not cameras, which are quite a different thing.

The only thing in common is lenses.

About like bringing up horses in a car forum.

 

[tenex]

Catching up...

Sorry, I haven't cited it properly: Performance of binoculars: Berek's model of target detection

A preprint version can be downloaded here on my webpage.

Thank you. I wasn't sure, but this is the same paper I had read some years ago in the context of another discussion here, so unexplained details in Omid's posts above must be coming from a different source. As you said, the Köhler-Leinhos approach clearly overvalues magnification in twilight conditions, when target detection itself becomes a greater challenge. Still their "twilight factor" remains a common element in binocular specifications, and not only at Zeiss. Perhaps you could propose a specific Berek-score forumla instead, and show how its ranking is more intuitively correct?

Here again you seem to be attributing too much agency to the ambient visual system itself. Any process incorporating tactile input[?] is more than a visual system.

My confusion here about inputs to what Omid called the "ambient visual system" was not addressed, but is resolved by this passage from Leibowitz/Shupert:
"The focal mode is almost, if not exclusively, visual while the ambient mode acts in concert with the vestibular, somatosensory, and auditory senses to subserve spatial orientation, posture, and gaze stability. In effect, we have a focal visual mode which is predominantly visual and an ambient system to which vision contributes along with vestibular and somatosensory inputs."
A broader "ambient system" needs to be distinguished from ambient vision itself.

(sneak preview: large apparent field of view in binoculars disrupts and confuses our ambient visual system leading to anxiety, fear and a sensation of motion sickness as tenex correctly noted in post #4).

Surely you mean small AFOV does? Although there must still be more room than I imagined for the ambient system to operate, since researchers seem to consider focal/central vision to be around 5-6°, while binoculars have ~60° AFOV, which of course is still a good deal less than normal vision.

This point has still not been followed up.

I did not find the Livingstone/Hubel or Fender papers particularly helpful, and the graph in post #10 remains unexplained.

My "magnified panorama" experiment (which you unsewered correctly) reveals another striking fact: It is impossible to create a magnified (or minified) 360-degree visual space. No matter what lens focal length or field of view or film size we use to observe/measure/record/perceive the space around us, the resulting 360-degree visual world will have to shrink back into "true world" in which the horizontal visual angle between any two objects remains invariant.

Of course I too answered correctly, as a matter of elementary geometry that didn't involve vision at all. I have no idea what the blue words here are even supposed to mean.

 

[Trinovid]

That's why you should never pan with your binoculars. The unusual optical flow in the peripheral part of field of view caused by combination of translational and rotational apparent motion will cause dizziness and headache.

Sorry, they work fine for me this way and the only binocular that gave me trouble was the otherwise incredible EL 12x50.

"Never" is "always" a bad term to use.

 

[wllmspd]

I agree that the range of reflectance values for things is in the 10-90% range. Not much gets>95% or below 1%. But what we see also depends on the illumination, if I have a scene with a mix of direct light and shadows the contrast will be much higher as the variation in illuminance can be many thousands to 1 possibly. Of course the brain auto white balances and colour adapts so we don’t easily notice this. Sounds like we need to get some forum members to sit in a dark room and run some of these tests so we can get more new data, as I think most visual science is carried out on quite small populations and not necessarily hugely diverse ones either (age and gender can have noticable effects and the “standard observer” is quite variable from what I can remember)..



Peter

 

[Holger Merlitz]

Catching up...

Thank you. I wasn't sure, but this is the same paper I had read some years ago in the context of another discussion here, so unexplained details in Omid's posts above must be coming from a different source. As you said, the Köhler-Leinhos approach clearly overvalues magnification in twilight conditions, when target detection itself becomes a greater challenge. Still their "twilight factor" remains a common element in binocular specifications, and not only at Zeiss. Perhaps you could propose a specific Berek-score forumla instead, and show how its ranking is more intuitively correct?

...

I fear that there is no such thing as a simple rule of thumb for the performance under twilight conditions. It is a situation in which the smooth crossover from daylight performance (in which magnification dominates) to night performance (in which objective diameter is of the essence) occurs, and the rate at which this crossover proceeds as a function of ambient light also depends upon the observer's eye pupil response. Any formula for binocular performance would necessarily contain the current luminosity L as a variable, and the eye-pupil diameter d(L) as a function of that. For strictly foveal observations and tasks which require observation of details (such as reading out the birds rings etc., under the condition that these details are not close to the threshold contrast), the twilight factor is probably a reasonable simplification.

Cheers,
Holger

 

[Omid]

If you run the math, you may find that the velocities of the image points differ between center and edge of field by no more than half a percent or so, which is no longer detectable. All image points in the virtual image thus move at practically equal velocities through the field, as if you were walking along a huge flat poster.

Hi Holger,

Sorry for my delayed response. Your analysis of the optical fellow pattern is accurate: the observer will see a uniform field motion where "all image points in the virtual image thus move at practically equal velocities" as you noted

Therefore, as such there is no problem with panning a binocular. As long as there is no distortion involved, that is.

I am afraid this is not the case. A uniform motion pattern over the whole field of view is not OK for the eyes. Please note that here I am not talking about whether the moving scene "appears" normal or slightly distorted to the viewer (the globe effect that you have studied in great detail in your book). The globe effect is a minor aesthetic issue. Panning with binoculars triggers a far more sinister physiological effect called Optokinetic nystagmus (OKN). I will explain this in a dedicated post shortly.

Regards,
-Omid

 

[Omid]

Why you should not pan with your binoculars

Panning with binoculars within the context of bird watching or wildlife observation means smoothly moving the binoculars across the field of view to scan a wider area. There are several reasons why this is a bad idea, but I just mention two here:

1. It triggers a physiological phenomenon called Optokinetic nystagmus.
2. It is useless for detecting wildlife.

Optokinetic nystagmus is a physiological phenomenon where the eyes move repeatedly in response to large, moving visual fields. It consists of repeated execution of two different types of eye movements: A slower smooth movement where the eyes track the moving visual pattern and a quick saccadic movement where the eyes rapidly snap back to the original position. The observer will not be aware of his rapid eye movements but after some time he or she will show various symptoms such as vertigo, dizziness, and motion sickness.

Optokinetic nystagmus is triggered by a uniform motion pattern across the field of view:

This phenomenon is a result of our optically operated "field holding" reflex which has evolved to maintain a constant view of a fixated target on our retina when we turn our head. We also possess a separate (and more ancient) inertially operated field holding reflex which uses the vestibular system in our inner ears to detect and compensate for head movements. But this latter system is not involved in the Optokinetic nystagmus.

Our oculomotor system and its controller nerve called 3rd cranial nerve are extremely precious. We should not endanger them by forcing our eyes into an involuntary, rapid and repetitive movement. Panning with binoculars can result in many symptoms such as blurred or shaky vision, difficulty with balance, and the sensation that surroundings are moving (oscillopsia).

No time to discuss Item 2 today.

-Omid

 

[Canip]

So, if I may repeat my question:
How do you follow a bird in flight with binoculars if you shouldn‘t pan?

I have been following birds in flight with my binoculars for many years now, esp. birds with a „predictable flight pattern“, such as birds of prey, storks, herons etc.

I fully understand what you say and what you mean by the symptoms triggered by panning. Everyone who has ever been panning for extended periods has probably experienced physiological effects. That‘s why you rest your eyes from time to time when using binoculars for longer periods of time.

I just haven’t figured out a way to follow birds in flight - necessary sometimes even for identifying species etc - without panning. Maybe you know how it’s done?

 

[Thotmosis]

I got dizzy from watching (the interesting) first video, in a way quite the same dizzying effect i had when using an NL Pure, with my Leica’s I never experience this. Is there maybe a relation?