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Why do eyes have to "focus" to different colors?

Hiemal

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I've noticed that when looking at the spectrum of people's laser collections on any computer, that when you view ...blues, or purples, your eyes tend to focus to them and then the other colors go out of focus. Same with viewing red, then blue and violet go out of focus.

Even though they're all technically the same distance from my eyes. :confused:

Why?
 

Blord

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I make a quote about Chromatic Aberration. :D

In optics, chromatic aberration (CA) is a type of distortion in which the lens is not able to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point.
 

DrSid

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Still I don't experience such phenomenon .. I mean I don't have to focus on different colors. I can't focus on blue on black .. that's right .. but that's all.
 

Cyparagon

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It is easier to see with the color difference is bigger. Try this - get an incandescent blacklight:



It produces mostly NIR, but some blue/violet. If you look at the filament, you will find it usually looks blue with a red halo (or sometimes red with a blue halo).
 

Teslanium

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The lens in the eye is a "simple" lens. Simple lenses don't correct for chromatic aberration, and focus shorter wavelengths closer to the lens and longer wavelengths farther away. I tend to notice this effect when looking at distant mercury-vapor streetlights at night; they tend to have violet/blue halos.


It's also very easy to see this effect by looking at a distant point light source through an equilateral dispersion type prism. You will notice that you can actually shift your focus along the spectrum - when focused on red, the rest of the spectrum diverges "conelike" toward the violet, and toward red when focused on violet. If you are near- or far- sighted you may even find it difficult to focus on one or the other end of the spectrum.

T.
 
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I don't really know if this is the answer, but if you shine through a diffraction grating with a blue laser, there is a shorter distance between the dots as with a red laser.
 

Atomicrox

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Yeah I notice that a lot. I've got miopy and I find it really hard to focus on shorter wavelengths. I can't even tell if my 405nm laser is properly focused from 50m away.

On the other hand I can focus red very well and things illuminated with red always seem better defined and crispier.

Wanna try something funny?
Swing your head left and right while looking at my sig (or any with a rainbow). The blue part will move "more" than your head, the green part will move "correctly" and the red part will move to the "wrong" side.
Not sure if it happens without glasses. I'm too blind to find out LOL
 
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Blord

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Yeah I notice that a lot. I've got miopy and I find it really hard to focus on shorter wavelengths. I can't even tell if my 405nm laser is properly focused from 50m aw.
I don't think anyone can focus the 405nm dot a few meter away. Our eyes are not use to look at this wavelength. I can't, the dot looks weird after few meters.
 
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I love the color of the new led style monitors, and I am using an Asus VE258Q as my desktop monitor, my old one had CFL back lighting, the new one is faster and more vibrant, but hurts my eyes after a few hours and I get optical illusions on almost every contrasting web page. I simply think the err "white" leds have a narrow peak compared to CFL and the extra contrast hurts my eyes. What does this have to do with focusing a dot from a 405, well its about contrast :p I can see a 405 dot clean on dark wood. To much contrast its out of focus, to little and it just all looks white, but stained wood is just about right. for me anyway.
 

Atomicrox

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On the wood you're mostly seeing fluorescence, not 405nm light, that's why it focuses better.
 
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let me put it put it like this then, I can focus my dot on blue surface or black surface but not on red or green surface, my eyes and brain have a limit, and contrasting colors have to hit the eye at a different angle to focus in the exact center to get a non blurry view. Or my brain cannot give me a clean image if the eye has to scan to many areas at once. Oh and some stains do indeed give off a very bright fluorescence glow, one of the things I love about a blacklight laser :p

this is just my observation, I have no clue the validity of it, other then what my brain projects to me as an image I do not understand the brain at all :beer:
 




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