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optical phenom

I had cataract surgery in one eye and will do the other one soon.

I have a pretty high power 400 nm laser. If I shoot it at the wall, the dot is bright with the repaired plastic-lens eye and invisible with the one that has the cataract. My doctor explained that a cataract absorbs blue light, and that's why some old ladies color their hair bluish-white, because then it looks right to them.

If I scan the laser around the room, some objects do show with the bad eye and some don't. That's because many "white" objects fluoresce to make them look whiter. Most things fluoresce greenish or purplish, but the giant old Radiotron Designers Handbook fluoresces red.

I have a 4FP7 CRT (DuMont, square-face, long-persistance, PDA) on a bookshelf and I can paint fun patterns on it.

That nearly-UV laser always gives me a mild headache.

Reply to
jlarkin
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My wife had both her lenses replaced, and commented on the improvement in her colour vision. The colours got a lot more subtle, what ever that means.

My optician assures me that I do have cataracts, but they aren't bad enough to be noticeable, let alone to be worth doing anything about.

Reply to
Anthony William Sloman

On a sunny day (Tue, 12 Apr 2022 17:09:47 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

I have one of those LED UV flashlight to check banknotes It looks bluish to me. When it shines on normal white paper it lights up brighter bluish -white.

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Reply to
Jan Panteltje

PS it is actually fun stuff, UV,

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I tried it among other things on London Tonic.. the quinine in it lights up. Also my old EPROM eraser lightbulb works the same way, but is better more powerful UV I think, do not look into it.

Reply to
Jan Panteltje

Am 13.04.22 um 02:09 schrieb snipped-for-privacy@highlandsniptechnology.com:

Reminds me at a guy in France some 200 years ago who discovered color blindness from the fact that he and his brother classified the color of flowers differently than other people, depending on sunlight or candles.

Gerhard

Reply to
Gerhard Hoffmann

We had a workman in the house once who mentioned that he was colour blind and could not see red at all. The sun was shining on a cut glass ornament projecting a spectrum on the wall. He pointed out the regions of the spectrum that he could see. The red end really was completely missing.

John

Reply to
John Walliker

What a co-incidence. Because as Wikipedia relates (

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), John Dalton and his brother in Manchester, England, also noticed the same thing. And colour- blindness is known as Daltonism after him... Dalton is known for lots of other topics and admittedly, Wikipedia says: "In 1822 he paid a short visit to Paris."

Reply to
Mike Coon

Red is fairly unusual fluorescence with 400nm excitation.

The colours you get tend to vary with rare earth impurities or various aromatic dyes. Washing powders contain a fairly potent blue fluorescer.

Bank notes and secure paper contain interesting flecks that show under the right wavelength of near UV light.

400nm is a wavelength capable of harming human eyes at high levels.

The solar Calcium K line filter at 394nm is sold as suitable only for photographic use for that reason. Eye damage is a real risk.

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"-(double-stacked).html Spec sheet has more info on the potential hazards at this wavelength:

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Reply to
Martin Brown

Our liquid laundry detergent fluoresces bright white, to make your clothes look clean and bright. I understand that they can be a laser medium.

My next choice will be the focal length of my left eye. My right one, with the plastic lens, focusses at 17". If I make the other one closer, I should have a pretty wide range of close vision, ideal for reading and computing and soldering. Brains are very good at stitching images.

Reply to
jlarkin
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I've noticed the same with old paperback data books, the red text on the cover often fluoresces orangey-red. Not new data books, probably because I don't have any.

Reply to
Clive Arthur

I will definitely look into that, I have a lot of floaters.

I noticed another interesting optical effect of cataracts during my last refraction - I could read the 20/20 line clearly twice in one eye. The two equally sharp images were completely separated with space in between, although the second image was lower contrast. Apparently cataracts are birefringent, with random orientation, the other eye has a smaller offset to the second image in a different direction. Very common according to my Ophthalmologist.

Reply to
Glen Walpert

The other direction is even more unusual, but is barely possible with

2-photon excitation.

The laser has a safety diffuser that scatters the light into a neat speckle pattern. Even looking at that reflected off a surface gives me a headache.

Reply to
jlarkin

I've always had a double image in one eye, before and after the cataract surgery. Some fold in the optics somewhere. I can map the boundary by scanning through a pinhole.

Reply to
jlarkin

We used to use NdYAG 266nm UV for sampling laser ablation quadrupled from the fundamental NdYAG 1064 line which still had more than a trace of the 532nm green line in it. Small spot size is everything in laser ablation sampling methods solid direct to plasma at the focus.

People with more money than sense had Xenon fluoride 351nm laser kit before the high power quadrupled laser source was perfected.

Seriously if you can see it as bright then it is capable inflicting eye damage. It really isn't a very friendly wavelength. The eye isn't very sensitive to it so you get no warning and the photons are energetic.

Nowhere near as bad as the hard UV of EPROM erasers though.

Reply to
Martin Brown

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