What is thinest of thin object which can be seen by necked eyes?

Answer 1

To expand upon where "Prince Ali"'s answer was going,
The thickness of the object is just one factor in determining an object's visibility. Distance obviously plays a big role, as well as the "quality" of one's eyes. Something a lot of people might fail to take into account, but does play a factor, is the "color" of the light used (not necessarily intensity).

Although one cannot really give you a definite answer as to the "thinnest of thin" object which can be seen, one could give you the physical limit in terms of angular size under a given wavelength of light with a view aperture of a given diameter (your eye).

The minimum angle (theta) able to be resolved with a circular aperture with diameter d, under light of wavelength lambda, is approximated as,
theta = 1.22 * lambda / d
Visible light is within about 400 nm and 700 nm in wavelength. A human eye (pupil) has a diameter of approximately 8 mm in dim light according to wikipedia.
If we assume 500 nm, dim, light...then the minimum angle able to be resolved would be about 7.625 E-5 radians.

Using a little trigonometry, one can figure out from this angle how large something would need to be (minimally) in order to be seen from a given distance.
sin (theta) = opp / hyp
cos (theta) = adj / hyp
tan (theta) = opp / adj
[I would draw some triangles, but it is really hard to do it well in Yahoo Answers, so I assume you can do this part]

The reason behind all this minimum angle stuff is due to the wave-like nature of light. Light will start to diffract, interfering (literally) with one's ability to resolve an image in the back of the eye.

Answer 2

Expanding on mrjeffy321's answer.

Mrjeffy describes the "blur circle" that is the minimum spot size to which an an optical system can focus light of a specific wavelength. The other thing that has to be taken into account is the size and density of receptors (rods and cones) in the retina of the eye. They act like individual light detectors that together detect the 2D image. In any optical system it is possible for the blur circle to be greater or smaller than the "detector" size. So the detector size can be the determining factor of the finest feature that can be resolved. I don't have the specific rod and cone dimensions handy, but I recall that the minimum spatial resolution of the eye is limited more by the receptor size than the optical blur circle.

Answer 3

Your question doesn't really make sense. I think you mean to ask "what IS the smallest object your eye can see" because there is a limit and then after that limit there are a lot of things which naked human eye cannot see. Remember that things like distance and lighting are also variables in this.

If I pull a hair out of my own head, I can see it on my hand. But if I put it 500 miles away, I don't think that my eye can see. But then, the sun and the moon are much further away but I can see them.

So I don't know what kind of an answer you are looking for.

Answer 4

Nichole Ritchie

Answer 5

Filamentous algae.

Answer 6

About 0.1 to 0.2 mm, depending upon how far away you are.

Answer 7

lol I agree with patrick nicole richie.

Answer 8

walls of a bubble

Answer 9

a layer of oil floating on water...

Answer 10

Your hair.