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Fairly straightforward question. If not, why not?

I suspect that if they do, it is not perceived due to the regions of highest dispersion being in one's region of lowest visual acuity.

Qmechanic
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Richard Terrett
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  • This page http://www.yorku.ca/eye/chroaber.htm claims: "You may be interested to know that the human eye lens exhibits chromatic aberration. Fortunately, a yellow pigment in the fovea called the macula lutea helps to protect us from this problem. Yellow pigments absorb blue light." This seems at best oversimplified and possibly completely wrong. However, it may be an effect that is relevant. –  Jun 02 '13 at 20:08
  • I came here searching for "why do I see 3 moons in different colours at night ?". Basically I see a white moon, a red moon with a little offset to top, and a blue moon with a little offset to bottom. Is this normal ? – frakod May 20 '21 at 14:56

4 Answers4

16

Yes, it does. We don't see it because our brain automagically 'correct it' because it always see the same aberration from the childhood.

Our eye focuses on 'green' wavelength as it's its peak sensitivity, so red and especially violet lines are usually slightly out-of-focus.

BarsMonster
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    This is the best answer here, but part 1 is incorrect. Chromatic aberrations are not fields aberrations; they exist on axis just as much as they do off axis. If you fix this I can give you an upvote. – Colin K Jul 22 '11 at 13:53
  • @Colin K You are right as usual :-) – BarsMonster Jul 22 '11 at 14:21
  • Oh man. I am tripping. I did not know about chromatic aberration until today (should have payed more attention in physics class I guess) and discovered it accidentally by looking at two numbers on an electronic device!

    One was blue and the other one was red. I was thinking about something else when I caught myself changing focus subconsciously back and forth and seeing either red in focus or blue but never both. So my "automagical" correction got broken? This is the first time I noticed it (I am in my forties).

     – Incassator Aug 25 '15 at 18:33
6

Here is an interesting webpage on the aberrations of the eye: http://www.telescope-optics.net/eye_chromatism.htm

According to http://kaschke-medtec.de/SS10/Exercise5.pdf the eye has quite a large chromatic aberration of 2 dptr across the visible range.

I heard (the rumor?) that for this reason the color bands in the french flag don't have the same width.

I also read of the interesting (and probably true) theory that the colour bands around edges actually help you to focus while you reading text. I think that explains why I find reading quite hard with LED illumination of small (non-overlapping) spectral bandwidth.

One could think it would be useful to wear color corrected glasses but I don't think that would help in any way (the aberrations due to the glasses will be small compared to the aberrations in the eye).

whoplisp
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  • Because You do not distinct the central (yellow spot, macula) area from the rest of the sensitive area, Your answer is misleading. – Georg Jul 22 '11 at 12:31
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    @Georg I thought about this after reading BarsMonster response. His answer doesn't convince me because the human lens has aspheric surfaces and an internal index gradient and the detectors are on an aproximate sphere. Therefore it is not obvious to me why central aberrations should be less. – whoplisp Jul 22 '11 at 14:03
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Because refractive index is a function of wavelenght, every lens experiences chromatic aberration, and so does a human eye.

This could have severe effect on human vision. However, eye has tuned spectral bandwidth - it is well known eye is most sensible to visible light which has wavelenght of 550 nm. Relative luminosity is also a function of wavelenght (in which more than 70% of the luminous energy is confined to a defocus range of less than 0.25 D defocus on either side of focus (if eye is optimally focused at 550 nm)). The exact spectrum to which we are sensitive, depends on light levels. Rods saturate at moderate and high light levels, so in this region spectral sensitivity is governed by cones. At lower light levels cones are no longer as sensitive and rods dominate the response. All this results in different spectral sensitivity for various luminosity and in this way eye is able to filter out some effects of chromatic aberration.

Ivana
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  • Could you elaborate a bit more how the eye can get rid of chromatic aberrations if you take into account sensitivity? I don't get your argument. – whoplisp Jul 22 '11 at 11:39
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I have a 405nm laser pointer, which emits light right on the edge of the visible spectrum. It is easy to see that this wavelength of light appears out of focus through the eye likely due to chromatic aberration. I would imagine this is because our eyes are not made to see that kind of light. I've also noticed that mercury vapor streetlights have a faint violet halo around them due to what I believe is chromatic aberration, since the violet light on the edge of the spectrum is refracted the most through our eyes.

user84547
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