• optical phenom

    From jlarkin@highlandsniptechnology.com@21:1/5 to All on Tue Apr 12 17:09:47 2022
    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.



    --

    I yam what I yam - Popeye

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  • From Anthony William Sloman@21:1/5 to jla...@highlandsniptechnology.com on Tue Apr 12 21:57:40 2022
    On Wednesday, April 13, 2022 at 10:09:58 AM UTC+10, jla...@highlandsniptechnology.com wrote:
    I had cataract surgery in one eye and will do the other one soon.

    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.

    --
    Bill Sloman, Sydney

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  • From John Doe@21:1/5 to jlarkin@highlandsniptechnology.com on Wed Apr 13 04:50:09 2022
    jlarkin@highlandsniptechnology.com wrote:

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

    You will clearly see the difference.

    Modern medicine is amazing, that is a good example. Assuming everything
    goes well.

    I woke up during mine. Could see some pixelated lights or whatever.
    Couldn't feel a thing. The doctor said "don't talk". I should have said
    "I'll be back" but instead I just shut up and went back to sleep.

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  • From John Doe@21:1/5 to All on Wed Apr 13 05:00:39 2022
    BTW... At the same time, they can remove "floaters" too.

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  • From Jan Panteltje@21:1/5 to jlarkin@highlandsniptechnology.com on Wed Apr 13 05:34:02 2022
    On a sunny day (Tue, 12 Apr 2022 17:09:47 -0700) it happened jlarkin@highlandsniptechnology.com wrote in <034c5hh182v4dj8cqurtaj6fgqs21uu14i@4ax.com>:

    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.

    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.
    https://www.ebay.com/itm/112135829056

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  • From Jan Panteltje@21:1/5 to All on Wed Apr 13 05:46:56 2022
    PS
    it is actually fun stuff, UV,
    https://www.thoughtco.com/what-glows-under-a-black-light-607615

    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.

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  • From Gerhard Hoffmann@21:1/5 to All on Wed Apr 13 08:19:48 2022
    Am 13.04.22 um 02:09 schrieb jlarkin@highlandsniptechnology.com:
    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.


    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

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  • From John Walliker@21:1/5 to Gerhard Hoffmann on Wed Apr 13 02:16:57 2022
    On Wednesday, 13 April 2022 at 07:19:56 UTC+1, Gerhard Hoffmann wrote:
    Am 13.04.22 um 02:09 schrieb jla...@highlandsniptechnology.com:
    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.
    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
    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

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  • From Mike Coon@21:1/5 to All on Wed Apr 13 11:19:48 2022
    In article <t35q24$qlfe$1@solani.org>, dk4xp@arcor.de says...

    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

    What a co-incidence. Because as Wikipedia relates (<https://en.wikipedia.org/wiki/Color_blindness>), 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."

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  • From Martin Brown@21:1/5 to jlarkin@highlandsniptechnology.com on Wed Apr 13 13:19:14 2022
    On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:
    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.

    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.

    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.

    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.

    https://www.baader-planetarium.com/en/baader-k-line-filter-1¼"-(double-stacked).html

    Spec sheet has more info on the potential hazards at this wavelength:

    https://www.baader-planetarium.com/en/downloads/dl/file/id/8/product/1399/important_notes_on_the_stacked_k_line_filter.pdf


    --
    Regards,
    Martin Brown

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  • From Clive Arthur@21:1/5 to Martin Brown on Wed Apr 13 15:39:59 2022
    On 13/04/2022 13:19, Martin Brown wrote:

    <snip>

    Red is fairly unusual fluorescence with 400nm excitation.

    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.

    --
    Cheers
    Clive

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to pNaonStpealmtje@yahoo.com on Wed Apr 13 07:28:45 2022
    On Wed, 13 Apr 2022 05:46:56 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    PS
    it is actually fun stuff, UV,
    https://www.thoughtco.com/what-glows-under-a-black-light-607615

    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.




    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.



    --

    I yam what I yam - Popeye

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  • From Glen Walpert@21:1/5 to John Doe on Wed Apr 13 15:25:13 2022
    On Wed, 13 Apr 2022 05:00:39 -0000 (UTC), John Doe wrote:

    BTW... At the same time, they can remove "floaters" too.

    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.

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to '''newspam'''@nonad.co.uk on Wed Apr 13 08:45:17 2022
    On Wed, 13 Apr 2022 13:19:14 +0100, Martin Brown
    <'''newspam'''@nonad.co.uk> wrote:

    On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:
    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.

    Red is fairly unusual fluorescence with 400nm excitation.

    The other direction is even more unusual, but is barely possible with
    2-photon 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.

    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.

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

    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.



    --

    I yam what I yam - Popeye

    --- SoupGate-Win32 v1.05
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  • From jlarkin@highlandsniptechnology.com@21:1/5 to All on Wed Apr 13 08:48:57 2022
    On Wed, 13 Apr 2022 15:25:13 GMT, Glen Walpert <nospam@null.void>
    wrote:

    On Wed, 13 Apr 2022 05:00:39 -0000 (UTC), John Doe wrote:

    BTW... At the same time, they can remove "floaters" too.

    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.

    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.



    --

    I yam what I yam - Popeye

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  • From Martin Brown@21:1/5 to jlarkin@highlandsniptechnology.com on Wed Apr 13 17:08:28 2022
    On 13/04/2022 16:45, jlarkin@highlandsniptechnology.com wrote:
    On Wed, 13 Apr 2022 13:19:14 +0100, Martin Brown
    <'''newspam'''@nonad.co.uk> wrote:

    On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:

    Red is fairly unusual fluorescence with 400nm excitation.

    The other direction is even more unusual, but is barely possible with
    2-photon excitation.

    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.

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

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

    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.

    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.

    --
    Regards,
    Martin Brown

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