optical phenom...

[server]

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

 

[Anthony William Sloman]

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

 

[John Doe]

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

 

[John Doe]

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.

 

[Jan Panteltje]

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

 

[Jan Panteltje]

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.

 

[Gerhard Hoffmann]

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

 

[John Walliker]

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

 

[Mike Coon]

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.\"

 

[Martin Brown]

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

 

[server]

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

 

[Clive Arthur]

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

 

[Glen Walpert]

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.

 

[server]

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

 

[server]

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

 

[Martin Brown]

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