Why can our eyes not focus on the violet dot?

[Greenhorn]

I first noticed this phenomenon when at a lecture. There was a small LED indicator light that was about the same color as a blu-ray (I hadn't built my laser yet), and from a distance it looked kind of like one of those plasma balls, with spikes sticking out in all directions. Then I built my laser, and if I shine it at a non-flourescing surface I can't focus on it, just like that violet LED. I can easily focus on the dot if I shine it at, for example, cotton, where it fluoresces bluish-white.

This phenomenon was mentioned in this thread http://www.laserpointerforums.com/forums/YaBB.pl?num=1219161671 , but not explained.

 

[daguin]

I first noticed this phenomenon when at a lecture.  There was a small LED indicator light that was about the same color as a blu-ray (I hadn't built my laser yet), and from a distance it looked kind of like one of those plasma balls, with spikes sticking out in all directions.  Then I built my laser, and if I shine it at a non-flourescing surface I can't focus on it, just like that violet LED.  I can easily focus on the dot if I shine it at, for example, cotton, where it fluoresces bluish-white.

This phenomenon was mentioned in this thread http://www.laserpointerforums.com/forums/YaBB.pl?num=1219161671 , but not explained.

This point doesn't help?

7) The eye has trouble seeing 405nm light. 405nm is "Near Ultra Violet" light. Blu-ray lasers are at the very edge of our eye's ability to see. Older people have more trouble and glasses with UV coatings filter it. Your eyes will get tired quickly when you first start using the blu-ray and the beam and dot may look "strange" to you. If you have read about IgorT's experiences you will have a better understanding.


Peace,
dave

 

[Switch]

My guess is that the reason is actually because it has a refraction index through the eye's mediums very different from wavelengths that we are used to seeing every day.

Can you unfocus your eyes? Try doing that on the dot.It works for me, it becomes focused, but everything else becomes blurry.

 

[Xplorer877]

It's weird a buddy of mine can focus on it either but I have no problem focusing on it. :-?

-Frank

 

[Switch]

It's weird a buddy of mine can focus on it either but I have no problem focusing on it. :-?

-Frank

You must have special eyes.Most people can't. :

 

[Greenhorn]

This point doesn't help?

7)  The eye has trouble seeing 405nm light.  405nm is "Near Ultra Violet" light.  Blu-ray lasers are at the very edge of our eye's ability to see.  Older people have more trouble and glasses with UV coatings filter it.  Your eyes will get tired quickly when you first start using the blu-ray and the beam and dot may look "strange" to you.  If you have read about IgorT's experiences you will have a better understanding.

Peace,
dave

I understand that the 405nm light is near the limit of what we can see - after all, when getting the true color by shining the laser at a non-flourescing surface, it's very dim, even though it's equivalent to my superbright, dazzling green.  But the red lasers are near the limit of visibility and they do not have the same qualities, so the fact that the violet lasers are near the edge of the visible spectrum doesn't explain why I can't focus on them.

The explanation about the refractive index kind of helps explain it.  Still, we see blue all the time and have no trouble focusing on it, and violet isn't too far from blue, so it's hard to believe that there would be such a huge difference.  Also, if it were merely a matter of refocusing the eyes to see that particular wavelength because of the difference in refraction through the eyes, it should just look blurry.  Instead, it looks spikey.

Deep violet light is a strange, mysterious beast.

 

[daguin]

I understand that the 405nm light is near the limit of what we can see - after all, when getting the true color by shining the laser at a non-flourescing surface, it's very dim, even though it's equivalent to my superbright, dazzling green.  But the red lasers are near the limit of visibility and they do not have the same qualities, so the fact that the violet lasers are near the edge of the visible spectrum doesn't explain why I can't focus on them.

The explanation about the refractive index kind of helps explain it.  Still, we see blue all the time and have no trouble focusing on it, and violet isn't too far from blue, so it's hard to believe that there would be such a huge difference.  Also, if it were merely a matter of refocusing the eyes to see that particular wavelength because of the difference in refraction through the eyes, it should just look blurry.  Instead, it looks spikey.

Deep violet light is a strange, mysterious beast.

I guess we will have to work with what "near" means. Red diodes put out an average 650nm. IR begins around 700nm. Red diodes are about 50nm away from "invisible." Violet diodes put out an average of 405nm. UV begins at 400nm. Violet diodes are only 5nm away from "invisible." If your violet diode is closer to the lower end of the "average", yours may be as low as 395nm. Since it is "almost" invisible, the eye/brain are working in unknown territory. They are doing the best they can, but different people will "see" it differently.

Peace,
dave

 

[Switch]

it should just look blurry. Instead, it looks spikey.

It just looks blurry to me. :-? Maybe it's the fact that you see a blurry dot on a focused background that looks weird.

the eye/brain are working in unknown territory

I still think the brain has less to do with it than the eye does.I swear I can focus on it if I try, but then everything else becomes blurry.This leads me to believe that the phenomenon is optical and not an artifact of our brain. :-/

 

[flogged]

I can focus on mine, but only when I'm close to it.

Apparently the human eye/lens combo focuses best on red/green - blue, and especially violet, not as well.

Also,  >95% of the color sensitive cells in the retina are red/green sensitive. Just a few are blue/violet sensitive. So peoples ability to discern contrast is much poorer using blue light, or when looking at blue objects - this can be measured.

Adding to the funk, when the eye is dark adapted the cells responsible for night vision (rod cells) are somewhat sensitive to 405nm - since these are the most numerous cells in the retina it may explain why the 405nm beam is very visible at night, but ghostly.

 

[lazerguy]

I use the same trick as Switch does. If the dot (or beam) is within a couple of meters, I simply unfocus my eyes, as if I intend to look at something really far away. Then, the dot/beam looks just as clear as a red or green one.

violet is truly a mysterious color, which is why I like blu-ray lasers.

 

[Benm]

My guess is that the reason is actually because it has a refraction index through the eye's mediums very different from wavelengths that we are used to seeing every day.

I think this theory might have merit.

Perhaps what happens is this: The eye will focus on whatever the dot is projected on, but that focus is valid for normal colors, probably best around the maximum visibility of 555 nm. Due to chromatic abberation this focus is slightly incorrect for different wavelengths, and gets worse the further you go (in)to the UV (or IR).

This gives a problem for the eye: it can focus on either the (texture of) the wall, or on the shape of the dot. Apparently, the first scenario happens and the dot seems sort of fuzzy.

One way to tell would be to put the dot on a completely smooth, even surface, and remove any other lighting. Ability to focus should be better then.

 

[pwnstar]

When I made my first bluray I was so confused why it was blurry. I thought I messed up my eyes cause I was tripping in the dark trying to look at it lol. but now I can focus on it a lot easier. I think after you play with it your eyes learn how to adjust better to the light.