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Focussing: Just Do It! (1 Viewer)

Omid

Well-known member
United States
PS. I also thought this article might be of interest to Omid, wrt the accommodation stimulus. Nah, you've probably read it. ;)

Thanks! I had not seen this one ;)

Here is my current understanding based on all that I have read and learned: As a biological creature who needs to see to function and survive, much of our "world" is outside the radius of 3m for which no accommodation is required. Accommodation is required to examine close objects, pick ripe fruits, eat food, etc. For all these tasks, the creature knows exactly where he is going to direct his eye gaze next, so his brain can directly tell his eye to accommodate, no need to spend so much "brain computational resources" to run a blur-based autofocus algorithm that will not be able to function at the end (since "blur" doesn't tell which direction should the lens focus).

There could be complementary/luxury focusing capabilities within our visual system that have been developed along with the development of color vision (itself also a luxury). But the primary focus mechanism is probably just a simple non-feedback reflex linked to eye convergence.

Brain is like a film director: he constantly tells our eye: Look here, focus here. Look there, focus there. A film director is not surprised by the unknown location of objects or characters in his set. He deliberately choses where the camera should look next and what angle of view and state of focus it should have.

The above "Hollywood theory" is my current understanding of human eye focus until I learn further... :rolleyes: :)

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Binastro

Well-known member
The eye may not take pictures, but the eye produces pictures in the brain.

These pictures in the brain may linger when the eye is covered.

Part of the picture may be assisted by memory and learning.

Whatever mechanism produces the pictures, the eye and brain are involved.

Also they are usually moving pictures, but distorted by faulty interpretation.
The pictures are certainly not flawless.

Regards,
B
 

Hauksen

Forum member
Antarctica
Hi Omid,

No. Lag of accommodation refers to the fact that human eye doesn't accommodate enough on objects which are too close and accommodates too much on objects which are far. At some intermediate distance (called the resting point of accommodation, about 80cm to 1.5m), the eye accommodates accurately

I see - thanks for the clarification!

a) Eye lens has so much chromatic aberration (and substantial spherical abberation) that focusing to produce a "sharp image" is literally meaningless (exactly as LeGrand said).

Well, from a computer science perspective, I woudn't the eye to produce a literal sharp image, but to extract key information from a series of appropriately focused images.

I'd imagine that probably, experiments with pictures shown only for very short amounts of time have been conducted to give a better impression of what the eye really can extract from a single picture instantaneously. However, that's probably a bit off-topic here (but fascinating nevertheless).


Very informative picture indeed, I had in fact been wondering what kind of resolution would be required to detect the chromatic aberration reliably. Of course, the question remains, which order of magnitude does the chromatic aberration have?

Regards,

Henning
 

Maljunulo

Well-known member
To be perhaps pedantic, the eye does none of that it is the image-combining and signal-processing center in the brain which “makes” the image out of pulses(?) from the retina via the optic nerve.

The eye, like many lens systems, performs better when it is stopped down. In bright sunlight I don’t need my glasses to read.
 

Tringa45

Well-known member
Europe
I'd imagine that probably, experiments with pictures shown only for very short amounts of time have been conducted to give a better impression of what the eye really can extract from a single picture instantaneously.
Hi Henning,

Chimpanzees are much better than humans at that:
I'm also beginning to suspect they might be better than some humans at designing scientific tests. :)

Regards,
John
 

Hauksen

Forum member
Antarctica
Hi John,

Chimpanzees are much better than humans at that:

Absolutely, there's certainly no reason to consider the human visual capacity to be anything outstanding!

A while ago, I read an article about the colour-differentiation capabilities of the typical bird's eye - which are so fantastic that it can be quite depressing to think about what we humans are missing out on, thanks to the convoluted path our eyes evolved on.

An engineer would have designed the bird's eye. The engineer who designed the human eye would have been fired ;-)

Regards,

Henning
 

Binastro

Well-known member
As to single image capability.

I could identify aircraft reliably at 1/10 second and sometimes at 1/50 second exposure with unaided eyes.

This is from photos.

In real life I could identify the aircraft by sound, so not a reliable eye experiment.

B.
 

Binastro

Well-known member
I think that birdwatchers can identify birds visually in less than 1/10th second.

I can see the flickering of old T.V. sets with side vision at 1/50th or 1/60th second.

A lady pilot saw the pulsing of a pulsar at 1/30 second before it was formally discovered.
She was not believed by the astronomer.

B.
 

Maljunulo

Well-known member
We had one of those at work, he drove everyone crazy complaining that his computer screen was “flickering” but no one else saw it.
 

Omid

Well-known member
United States
Absolutely, there's certainly no reason to consider the human visual capacity to be anything outstanding!

An engineer would have designed the bird's eye. The engineer who designed the human eye would have been fired ;-)

Less than two months ago, I was invited to a prominent optical manufacturing company in Europe. During my visit, I gave a 3-hour talk on Visual Perception for the company's executives and R&D engineers. I organized my talk in two parts. During part one, I considered the human eye as a camera and compared its image forming capabilities with a modern photography camera. The logical conclusion was that the eye rates very poorly when considered as a camera. I finished the talk by presenting quotes by Drs. Rafael Navarro (a prominent vision scientist from Spain) and Trevor Lamb (a prominent scientist from Australia) which pointed several contradictory or inefficient design features of the human eye.

After a coffee break, we started Part II of the talk where the eye was seen in a very different light...

:)

-Omid
 

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Hauksen

Forum member
Antarctica
Hi Omid,

After a coffee break, we started Part II of the talk where the eye was seen in a very different light...

Cool presentation, thanks a lot for sharing! My favourite is the angular diagram on "Human visual attention". I suppose "text" means that one is able to read text within a centered 20° cone?

Regards,

Henning
 

Omid

Well-known member
United States
Hi Omid,
Cool presentation, thanks a lot for sharing! My favourite is the angular diagram on "Human visual attention". I suppose "text" means that one is able to read text within a centered 20° cone?

Regards,
Henning

Thank you and sorry for late reply.

Yes, that's what it means. The sharp field of view of human vision is only 0.5 to 1 degree wide depending how strictly you define sharpness. This means, in your typical binoculars with 60-degree apparent field of view, only 1/3600 of the visible area is seen sharply at any given time!! The entire field of view is perceived via a series of scans whose exact order we don't remember consciously. The Russian scientist Alfred Yarbus has made numerous studies of human eye movements when examining a scene.

The "unsharp" part of human's field of view is used for proprioception (figuring out where we are in the world) and detection of movement (both self-movement and movement of other objects).

A most astonishing fact: In humans and other primates, the visual information is branched into 6 parallel pathways after going through the Lateral Geniculate Nucleus (LGN). Four of these pathways carry color information while the other two carry only luminance information. Perspective, stereoscopic vision, form and movement are processed by the pathway which is not color selective!

One part of the brain works only in black-and-white and creates line-drawings of the visual world. Another part of the brain paints these line drawings if time permits! :)

See Margaret Livingstone and David Hubel, Segregation of Form, Color, Movement, and Depth: Anatomy, Physiology, and Perception, Science, Vol. 240, May 1988 (Dr. Hubel won the Nobel Prize for his work on eye physiology in 1981. He has passed away. His student, Dr. Livingstone, deserve to win one as well.)





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Binastro

Well-known member
I notice with an 8 inch fan that I get a resonance with my vision on the medium speed setting.
There is medium and fast.

From say 2 feet away.

The fan blade either moves slowly backward or maybe slowly forward.

I presume that this means my imaging has a frequency of so many frames a second.

Is there a recognised frequency of human vision?

The effect is similar to wagon wheels in old movies depending on the frames per second and wheel speed.

Regards,
B.
 

Binastro

Well-known member
Yes, there is fluorescent lighting in the kitchen.
A 6ft tube.

Thanks.

I'll try in another room.

With 103F outside on Tuesday and 89F in the kitchen, I have had the fan on this week.

I tried, unsuccessfully, to photograph the blades, to get the speed.
The screen of the Canon G15 flickers in the kitchen also.

Regards,
B.
 

Troubador

Moderator
Staff member
Supporter
Thank you and sorry for late reply.

Yes, that's what it means. The sharp field of view of human vision is only 0.5 to 1 degree wide depending how strictly you define sharpness. This means, in your typical binoculars with 60-degree apparent field of view, only 1/3600 of the visible area is seen sharply at any given time!! The entire field of view is perceived via a series of scans whose exact order we don't remember consciously. The Russian scientist Alfred Yarbus has made numerous studies of human eye movements when examining a scene.

The "unsharp" part of human's field of view is used for proprioception (figuring out where we are in the world) and detection of movement (both self-movement and movement of other objects).

A most astonishing fact: In humans and other primates, the visual information is branched into 6 parallel pathways after going through the Lateral Geniculate Nucleus (LGN). Four of these pathways carry color information while the other two carry only luminance information. Perspective, stereoscopic vision, form and movement are processed by the pathway which is not color selective!

One part of the brain works only in black-and-white and creates line-drawings of the visual world. Another part of the brain paints these line drawings if time permits! :)

See Margaret Livingstone and David Hubel, Segregation of Form, Color, Movement, and Depth: Anatomy, Physiology, and Perception, Science, Vol. 240, May 1988 (Dr. Hubel won the Nobel Prize for his work on eye physiology in 1981. He has passed away. His student, Dr. Livingstone, deserve to win one as well.)





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Presumably the part of the brain responsible for the application of colours to a scene we view does this by responding to the frequencies of the light in order to select an appropriate colour from (another presumption) a 'database' of colours built into our brains by our homo sapiens DNA.

Lee
 

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