what is the smallest thing the human eye can see?

Answer 1

A single human eye sees roughly a 140-degree field horizontally and a 90-degree field vertically. The eye's resolution capability varies over the area of the retina and therefore with viewing angle. It is highest in the foveal, or straight-ahead, viewing region of the retina, which lies within a 2- to 4-degree radius of the optical axis of the eye, where an angular separation of about one arc minute may be detected under ideal conditions.

The eye can rotate 45 degrees vertical, so the foveal region may be directed to view any part of a 90- to 95-degree section of the horizontal monocular field of vision. Solving the previous equation using an angle of 60 arc seconds or 0.01667 degree, we find that the distance at which the foveal region of the 20/20 eye may resolve lines 1 mm apart is 3,438 mm or about 11.3 feet.

You can check the resolving power of your own eyes by drawing two lines spaced 1 mm apart on a piece of white paper, using black ink to maximize contrast. Hang the paper on the wall, back up until you reach that point at which you can still just discern two lines, but stepping further back results in your seeing a single line. Measure the distance from your eyes to the paper. Check with the lines oriented both horizontally and vertically to verify that resolution is virtually the same in both dimensions.

Answer 2

There are three factors present in this question and that is,
1) How good is the person's eyesight.
2) Is the smallest thing mean "by any means" or do you mean by unaided eye.
3) You can see small items but any detail is lost. For example you can see a human hair but no surface detail or you can see the surface detail of a matchstick but not the individual cell structure that creates that surface detail.

A more simple direct answer is my eyesight when I was 20 was close to ideal but now is so bad I have trouble reading 1/4" print without strong glasses. The smallest thing I have ever seen on a continuous basis was very fine copper wire I used for making electronic inductors. The smallest thing I have seen with the aid of technology is the blurry sphere of a large atom, it was blurry because most atoms by nature vibrate at room temperatures.

Answer 3

The smallest thing which the eye can see it technically does not actually see it as the human brain observes a finite particle then totally disregards it as irrelevant, otherwise the brain would be continually processing information it has no use for; using valuable processing function.

Answer 4

Most people can see Paramecium swimming in a culture, if they hold a glass tube of the culture up to the light. But most people cannot see individual Euglena in culture, by the same method. The Paramecium measure about 200 micrometers, or 0.2 millimeter. The Euglena are about 40 to 50 micrometers.

Answer 5

You know those floaters you see in your eyes sometimes? Well, they are cells shed from your eye. Sometimes you can see a round shape in them, which is the nucleus - so you could say the smallest thing a human eye can see is the nucleus of a cell!

Answer 6

What Paul above said, but I could see smaller ciliates, less than 100 um, as distinct moving dots, when I was a kid. Now? Forget about it. I'm old.

Answer 7

Specks of dust. I think. Hey I have a source look at it see what you find. Tell me if I'm right or not I'm just guessing.

Answer 8

depends on the eye or the glasses ..

also depends on the number of alcoholic beverages consumed.

people other cars bridges could be too small..

Answer 9

With or without a f*kin great microscope?

Answer 10

those dust particles you can see when the sun shines really brightly through a window!