h a l f b a k e r yWarm and Fussy
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Instead of wearing sunglasses, wear opaque contact lenses with just a tiny pinhole in the centre. You'd get images just as dim as with sunglasses, but with the advantage of near-infinite depth of field (translation: everything, from a few inches away to infinity would be in perfect focus) and colours
would be unaffected.
MkI pinhole contact.
http://i923.photobu...%20MkI/IMG_5419.jpg
And yes that's a photo of Feynman in the background. [MaxwellBuchanan, Jul 07 2011]
[link]
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Nice idea. Trouble is, if you got on a bus or the sun went in, they'd be a lot more difficult to take off than sunglasses. You would also really need to take them off, because your pupils dilating wouldn't have any effect - you'd effectively be blinded. They would only work when light levels were constant. |
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Except they would cause people to go blind. Sunglasses are good for your eyes because they reduce the quantity of light, and because they either contain, or are made from materials that block UV-A and UV-B light. The UV component of sunlight is what is actually causing the damage. Pinhole contacts, by their nature, can't protect from UV light. They would make your pupils expand, letting in even more damaging uv rays than if you were weren't wearing sun protection at all and the pupils contracted naturally to reduce the amount of light entering the eye. |
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Contact lens materials filter out a fair amount of UV by themselves. The small aperture of the lens would further reduce UV tranmission. The argument that pupil expansion would let it more UV is not valid, because the opaque part of the contacts would not let through any UV. Total UV exposure of the cornea would be far reduced, perhaps more then with sunglasses. |
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As aj wrote, they would reduce your ability to adjust to different light conditions. In bright sunlight this disadvantage may be outweighed by the benefits of the contacts. |
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I'd like to try them out. Wish I could buy some, but perhaps they can be homemade from cosmetic contact lenses. Anyone know of a safe way to coat these with a dark material? |
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Contact lens materials filter out a fair amount of UV by themselves. The small aperture of the lens would further reduce UV tranmission. The argument that pupil expansion would let it more UV is not valid, because the opaque part of the contacts would not let through any UV. Total UV exposure of the would be far reduced, perhaps more then with sunglasses. |
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As aj wrote, they would reduce your ability to adjust to different light conditions. In bright sunlight this disadvantage may be outweighed by the benefits of the contacts. |
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I'd like to try them out. Wish I could buy some, but perhaps they can be homemade from cosmetic contact lenses. Anyone know of a safe way to coat these with a dark material? |
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It seems that there is an international patent covering pinhole contacts, dating from 2007. |
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I think the point about infinite depth of field is excellent!! |
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To overcome the adaptability problem, how about lenses
with concentric circles of light-reactive pigment,
progressively less sensitive. In bright light, all the
pigment rings would darken, giving you the full benefit of
the pinhole. |
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As the light dimmed, progressively wider rings would
become transparent, creating a sort of solid-state iris
effect. |
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//Anyone know of a safe way to coat these with a dark
material?// |
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If you have rigid lenses, you can use ordinary aerosol paint;
just mask off the central area and spray very lightly on the
*outside* surface until you build up the opacity. Then leave
at least overnight to dry thoroughly. I made a pair of gold
contacts this way. |
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And don't get any dust on them while the paint's drying. |
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Very odd. I just thought (or thought I'd thought) of this, and
Googled "pinhole contacts" before posting it. This page was
the top hit. |
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Even odder and more disturbing, I didn't even recognise my
annotations from a mere two months ago. I think my short-
term memory is going. |
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Even worse, I think my short-term memory is going too. |
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Even odder. Once again, the idea of pinhole
contacts popped into my head, because I'm now
both short- and far-sighted and want something that
will solve all problems. Once again, I found myself
back at this page. Once again, I had completely
forgotten about it, and about having annotated it. |
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It gets worse. I was about to say something about
my memory being lousy when I realized I'd already
said that in my last annotation. |
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"Great minds run in the same channel." Or "rut" as
the case may be. |
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Try piercing an index card with pinholes --
MULTIPLE pinholes, closely spaced -- and holding
that up to one eye, as close as you can get it. It's
an old trick for testing visual acuity in people with
refractive error who forgot their spectacles. It
does
what you want, which is to correct myopia and
presbyopia simultaneously with a single "lens." |
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Some experimentation with size and spacing of
pinholes is required, or you can buy a plastic
version from a vendor of medical equipment. |
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Done that. Also just tried a pinhole in a small piece
of foil held against my contact lens. Works fine -
focus from about 1 inch to infinity. Next step is to
paint up some contacts. |
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The problem of reduced light adaptation is trivially solved by carrying a few-kw floodlight. (Batteries in backpack or handcart). |
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(Max), forgetting and rediscovering your annos is part of the joys we all owe [Jutta] for. I periodically find an idea on [recent] and compose a witty response while reading it, and then go "Oh, I was here a few years ago...never mind." |
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Someday I'll tell you about my plan for my Alzheimers mom and my brother's Alzheimers mother-in-law. |
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Did that make any sense? Leaving the site now, see you next week. |
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That's nothing - *I'd* completely forgotten about this
idea, and apparently I wrote it. |
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// want something that will solve all problems // |
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We can help. Assimilation into the collective will solve all your current problems in one go. We'll even throw in a handy laser pointer on the side of your head. |
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I read this as Pinhole Contracts.... small print that is even smaller! |
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If you wear contacts for short-sightedness, but are
also getting far-sighted (like me), pinhole lenses
would seem a good option. With a 1mm pinhole
(in a piece of foil, held just touching the front
surface of one contact lens) I got sharp focus over
the entire visual range. |
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My Googling found "pinhole" contacts, but only for
certain eye diseases; and they often had
concentric zones of different power, rather than a
simple pinhole. Given that pinhole glasses are
well-known, there must be some good reason why
pinhole contacts aren't common, but I'll have to
do the experiment to find out what that reason is. |
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My previous attempts at painting lenses (many
years ago) were fine, but a sharp pinhole would
involve a sharp edge to the paint (which was on
the outer surface). We have a metal evaporator
at work, though, so it ought to be possible to
deposit a gold film with a pinhole (gold films are
opaque even when very thin, avoiding the
problem of sharp paint-edges). |
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You're not getting far-sighted - that's hyperopia
(which is what I've got). What you've got is
(probably) presbyopia - the age-related decline in
the flexibility of the eye's lens, which means you
can't focus as close as you used to be able to. |
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If having presbyopia makes you cry are you then a presbyterian? |
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// What you've got is (probably) presbyopia// |
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What utterly amazes me is that presbyopia is seen
as a normal and unavoidable degeneration, and
there seem to be no drugs being developed to
reverse the hardening of the lens. Given that it's
a very well-understood process involving
essentially a single protein (crystallin, if memory
serves), it should not be too difficult a problem to
solve. |
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// no drugs being developed to reverse the hardening of the lens // |
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There are drugs to stop you caring about it though. Ethyl alcohol is particulalrly good in this respect. |
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The MkI pinhole contact lens was not a complete
success. For one thing, I only had red acrylic
spray-paint. For another thing, the hole wasn't
crisp enough and had fadey edges. And for yet
another thing, I forgot that contacts are designed
to slide around a bit, so the damned hole wouldn't
stay central. |
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However, it was painless, and the focus (though
not great) was roughly the same from about 8
inches to infinity, I think. |
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