Does the human eye magnify objects?

[LightningInAJar]

TL;DR Summary

Scale of human vision.

Does the human eye see things at the correct size or is there such a thing? I know one of my eyes sees things slightly smaller than the other, but ideally should the eyes biologically not magnifying or shrink anything at all?

 

[russ_watters]

Does the human eye see things at the correct size or is there such a thing? I know one of my eyes sees things slightly smaller than the other, but ideally should the eyes biologically not magnifying or shrink anything at all?

Is that even a thing? (my answer: no). What does "correct size" mean?

 

[Rive]

Does the human eye see things at the correct size or is there such a thing?

No/does not matter. Just think about eyeglasses: all of them modifies the size of objects seen.
Size correction/matching/sense happens in the brain.

 

[BillTre]

Eye glasses among other things are to make the image land on the plane of the retina instead of in front of or behind it, or make the image sharper.

One might consider that a change in magnification, WRT the eye, would change the number of photo-receptors that an given size object in the visual field would illuminate. Glasses don't do much of that unless they are magnifiers, or a telescope or something like that.

 

[Filip Larsen]

Perception of object size is tied with depth perception, and in general depends on a lot of factors, while the actual optical magnification of the eye fair is more or less fixed.

 

[Tom.G]

Just think about eyeglasses: all of them modifies the size of objects seen.

Well, yes, to a minor extent though.

Eye glasses among other things are to make the image land on the plane of the retina instead of in front of or behind it

Eye glasses are placed close to the existing eye lens, approximating a compound lens. (https://byjus.com/physics/compound-lenses-thin-lenses-in-contact/) This has the effect of changing the focal length of the existing eye lens.

For the far-sighted, a positive (convex) lens will shorten the effective focal length to bring close objects into focus on the retina. For the near-sighted a negative (concave) lens will bring distant objects into focus

A positive lens can be used as a magnifier simply by moving it further from the eye. A negative (concave) lens moved away from the eye makes the world look smaller.

Hope this helps!

Cheers,
Tom

 

[Godot_]

To answer the thread's title question "Does the Human eye magnify objects":

No. Quite the opposite...

Also, how should that work? The retina is a wee little spheroid thingie, less than an inch - the stuff outside is way bigger...

From a purely physical viewpoint, it reduces objects' sizes. The human eye's lens has a refractive power of about 18dpt when relaxed (i.e. not actively focussing), and the cornea / anterior chamber system has a power of 40-ish dpt. The total refractory power of the eye's optical apparatus is 59dpt. This is pretty constant throughout all humans. Hyperopia and myopia come from the eyeballs' size being smaller or larger than the ca. 24mm they should be... ...then the retina is out of focus of the (relaxed) lens + cornea, and the projected image gets blurry. In the ccase of mild hyperopia, the accomodation apparatus can still contract the lens to increase its refractory power, and thus compensate the reduced rear focus length.

Pages 6-10 in this physiology script here explain the optical apparatus quite nicely and concisely.

If you cut out the retina and the interfering brain, and find some very brightly lit stuff, to look at, you should be able to project a magnified image, onto the rear of your skull, though.
/sarcasm

 

[BillTre]

If you cut out the retina and the interfering brain, and find some very brightly lit stuff, to look at, you should be able to project a magnified image, onto the rear of your skull, though.

Reminds me of the snail lip-brain prep a lab I used to know used to use to study a simple case of learning.
They would cut out the snail's lip and attached brain, put it in a culture dish, and poke it with electrodes. They could then watch a specific case of learning at the electrophysiological level.

 

[pinball1970]

Summary:: Scale of human vision.

Does the human eye see things at the correct size or is there such a thing? I know one of my eyes sees things slightly smaller than the other, but ideally should the eyes biologically not magnifying or shrink anything at all?

The eye does not 'see,' the brain does, would be my answer. The eye collects data and the brain interprets that data to the correct size as the per real world. Add to that colour, distance, moving and static.
Evolution has refined that process so we do not run into trees with think are far away but are actually inches away, take on a rival twice our size or jump off a small hill that is high enough to injure us.
Another thing is we imagine awake and dream asleep without optical input quite happily.

 

[jim mcnamara]

Thanks for all the responses. Eyes do exactly the opposite of what was asked: that is reduce the "size".
Relative size perception is in the brain, not the eye. Nice secondary school level read:
https://www.brainfacts.org/thinking-sensing-and-behaving/vision/2012/vision-processing-information

Thread closed.