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Joined: Jan 2001
Posts: 13,858
Carpal Tunnel
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OP
Carpal Tunnel
Joined: Jan 2001
Posts: 13,858 |
When macular degeneration impairs macroscopic vision,
*magniscopic* vision may help. The ability of lenses to magnify is a function of their focal length, which is measured in diopters:
diopter
n.
5Fr dioptre < L dioptra < Gr instrument for leveling, etc. < dia3, through + base of opsis, sight < ops, EYE6 a unit of measure of the power of a lens, equal to the power of a lens with a focal length of one meter
di[op4tral
adj.
If I remember correctly, a four diopter lens has a focal
length of a quarter of a meter.(Hey, Bean, am I right?_)
So I have a six inch four diopter lens to help me read my
monitor.
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Joined: Jan 2001
Posts: 1,156
old hand
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old hand
Joined: Jan 2001
Posts: 1,156 |
If I remember correctly, a four diopter lens has a focal length of a quarter of a meter.(Hey, Bean, am I right?)Yup, right on. I'm impressed with your memory, too - I had to LIU in my optics book! 
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Joined: Jan 2001
Posts: 13,858
Carpal Tunnel
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OP
Carpal Tunnel
Joined: Jan 2001
Posts: 13,858 |
Thanks, Bean. I'd like to try a larger lens with a wider field. It is tiring having to hold and move this lens. It is part of a light such as draftsmen use, It at one end of an arm with three pivoting joints, with counterbalancing springs. Originally the lens was surrounded by an 8 inch circular fluorescent, which is too bright to use. Edmund Scientific apparently doesn't have the big lenses they used to. Of course, a Fresnel lens doesn't give a sharp enough image.
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Joined: Aug 2002
Posts: 2,154
Pooh-Bah
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Pooh-Bah
Joined: Aug 2002
Posts: 2,154 |
My Mom has MD too although not yet as advanced as yours. She was given a sheet of clear yellow celophane by someone who thought it changed brain function somehow to improve reading. I was deeply skeptical but it did help. I think it had more to do with increasing contrast and reducing glare than brainwaves though.
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Joined: Oct 2000
Posts: 5,400
Carpal Tunnel
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Carpal Tunnel
Joined: Oct 2000
Posts: 5,400 |
Re:a sheet of clear yellow celophane...to improve reading.
Interesting. Yellow/black is purported to be the best constant for human vision.
i have used clear red acetate sheets to test 'readability' factors in web pages (for the visually handicapped) Red acetate reduces contrast to a large degree, so you can see when contrast is provided by color alone, and when it is provided by hue or light intensity. with this test, navy blue on light blue is still readable, but medium blue on grey often isn't. (it would be very readable by someone with normal vision, but not any one who has MD, or other problems with visual accuity, (normal aging decrease visual accuity!).
i can occationally* see Venus an hour or two after the sun comes up.. (just as i can see the moon in the day time sky) but when i was younger, i could often** see it.. now it fades.
*once or twice a year in a good year!
**two or three days in a row, till mid morning!(but still only at max a half dozen times a year!)
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