OT, Zenni Optical help!
Thanks everyone for helping me about 4 weeks ago with my questions re
'progressive' lenses. I am now ready for bifocals. The progressives are wonderful for garage sales and the supermarket. I no longer have to get on my knees to read phono album and book titles. They are useless for all other purposes. I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Any and all help greatly appreciated. Ivan Vegvary |
OT, Zenni Optical help!
Ivan Vegvary writes:
I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Change both adds to +1.5, instead of +2.5. Why: The spherical/cylindrical lens should correct your vision for focusing at infinity. The additional positive refraction (the "add") is specified in diopters, which is the inverse of the focal length in meters. If you hold a lens of power d in diopters in front of your infinity-focused eyes, you will then focus instead at 1/d meters. So a +1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which for most people is a suitable computer screen reading distance. Your 2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from your face, suitable for books. So whatever distance you want to sit from the screen, in meters, invert that and specify it as the "add" number. Rather than bifocals for the computer, you might consider single-vision lenses so you're not tipping your head about to read the screen. For that you would specify no add, and instead add 1.5 to the spherical Rx numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00. |
OT, Zenni Optical help!
"Richard J Kinch" wrote in message .. . Ivan Vegvary writes: I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Change both adds to +1.5, instead of +2.5. Why: The spherical/cylindrical lens should correct your vision for focusing at infinity. The additional positive refraction (the "add") is specified in diopters, which is the inverse of the focal length in meters. If you hold a lens of power d in diopters in front of your infinity-focused eyes, you will then focus instead at 1/d meters. So a +1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which for most people is a suitable computer screen reading distance. Your 2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from your face, suitable for books. So whatever distance you want to sit from the screen, in meters, invert that and specify it as the "add" number. Rather than bifocals for the computer, you might consider single-vision lenses so you're not tipping your head about to read the screen. For that you would specify no add, and instead add 1.5 to the spherical Rx numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00. Richard, thank you for your insightful reply. However, I want to be sure that we are talking about the same thing. I often have to do computer work (1.5 reading glasses work fine) while at the same time I am making entries from a hand held manual or drawing. For that I have to take off my computer glasses (1.5) put on my reading glasses (2.5) read a sentence or dimension, replace my computer glasses and make a keyboard entry. I was hoping to find a bifocal that will allow me to do both with one set of glasses. Please advise. Thank you Ivan Vegvary |
OT, Zenni Optical help!
"Ivan Vegvary" wrote in message ... "Richard J Kinch" wrote in message .. . Ivan Vegvary writes: I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Change both adds to +1.5, instead of +2.5. Why: The spherical/cylindrical lens should correct your vision for focusing at infinity. The additional positive refraction (the "add") is specified in diopters, which is the inverse of the focal length in meters. If you hold a lens of power d in diopters in front of your infinity-focused eyes, you will then focus instead at 1/d meters. So a +1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which for most people is a suitable computer screen reading distance. Your 2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from your face, suitable for books. So whatever distance you want to sit from the screen, in meters, invert that and specify it as the "add" number. Rather than bifocals for the computer, you might consider single-vision lenses so you're not tipping your head about to read the screen. For that you would specify no add, and instead add 1.5 to the spherical Rx numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00. Richard, thank you for your insightful reply. However, I want to be sure that we are talking about the same thing. I often have to do computer work (1.5 reading glasses work fine) while at the same time I am making entries from a hand held manual or drawing. For that I have to take off my computer glasses (1.5) put on my reading glasses (2.5) read a sentence or dimension, replace my computer glasses and make a keyboard entry. I was hoping to find a bifocal that will allow me to do both with one set of glasses. Please advise. Thank you Ivan Vegvary OK, add 1.5 to the main prescription and then make the bifocal only +1. YMMV but I have the same issue, I'd go +1 on the main prescription and have +1.5 on the bifocals. Means the computer has to be 6 or 8 inches farther away OD SP +2.25, Cyl -0.75, Axis 098, Read Add +1.0 OS SP +2.50, Cyl -0.50, Axis 110, Read Add +1.0 for your request. Karl |
OT, Zenni Optical help!
Richard J Kinch wrote:
Ivan Vegvary writes: I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Change both adds to +1.5, instead of +2.5. Why: The spherical/cylindrical lens should correct your vision for focusing at infinity. The additional positive refraction (the "add") is specified in diopters, which is the inverse of the focal length in meters. If you hold a lens of power d in diopters in front of your infinity-focused eyes, you will then focus instead at 1/d meters. So a +1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which for most people is a suitable computer screen reading distance. Your 2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from your face, suitable for books. So whatever distance you want to sit from the screen, in meters, invert that and specify it as the "add" number. Rather than bifocals for the computer, you might consider single-vision lenses so you're not tipping your head about to read the screen. For that you would specify no add, and instead add 1.5 to the spherical Rx numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00. I am currently looking at new glasses for the wife. Her problem is that she can see fine without correction out to 20-24" After that the world becomes a big blur. What I tried to talk to the doc about was a pair of bifocals with correction on top and none on the bottom, he looked at me like I was nuts. I would think it was a more common thing than what he seemed to think. OD SP -2.75, Cyl -0.25, Axis 175 OS SP -2.75, Cyl -0.75, Axis 155 Someone have an idea? Other than a new wife.... -- Steve W. |
OT, Zenni Optical help!
In article ,
"Ivan Vegvary" wrote: "Richard J Kinch" wrote in message .. . Ivan Vegvary writes: I want to order some bifocals, and obviously I will use the same prescriptions. OD SP +0.75, Cyl -0.75, Axis 098, Read Add +2.5 OS SP +1.00, Cyl -0.50, Axis 110, Read Add +2.5 However, I would also like to order a pair for the computer. I use +1.5 reading glasses for the screen, and switch back and forth to +2.5 reading glasses for reading. If I want bifocals that do the same thing (obviate the switching) what numbers do I use? Where do I plug in the +1.5 value? Change both adds to +1.5, instead of +2.5. Why: The spherical/cylindrical lens should correct your vision for focusing at infinity. The additional positive refraction (the "add") is specified in diopters, which is the inverse of the focal length in meters. If you hold a lens of power d in diopters in front of your infinity-focused eyes, you will then focus instead at 1/d meters. So a +1.5 add will focus at about 1/1.5 = 0.67 meters, or about 2 feet, which for most people is a suitable computer screen reading distance. Your 2.5 add let you read a book 1/2.5 = 0.4 meters, or about 16 inches, from your face, suitable for books. So whatever distance you want to sit from the screen, in meters, invert that and specify it as the "add" number. Rather than bifocals for the computer, you might consider single-vision lenses so you're not tipping your head about to read the screen. For that you would specify no add, and instead add 1.5 to the spherical Rx numbers, that is, 2.25 and 2.50 instead of 0.75 and 1.00. Richard, thank you for your insightful reply. However, I want to be sure that we are talking about the same thing. I often have to do computer work (1.5 reading glasses work fine) while at the same time I am making entries from a hand held manual or drawing. For that I have to take off my computer glasses (1.5) put on my reading glasses (2.5) read a sentence or dimension, replace my computer glasses and make a keyboard entry. I was hoping to find a bifocal that will allow me to do both with one set of glasses. Please advise. It's a reasonable combination to have computer glasses above and reading glasses below in the same pair of bifocals. Joe Gwinn |
OT, Zenni Optical help!
BQ340 writes:
For example how would I specify a pair of bifocals that give my say 3X at 2'? Eyeglasses do not do that. Reader eyeglasses do not magnify per se; what they do is move the near point (how close you can hold something in focus) closer to your eye. The standard distance of 10 inches is considered normal closest reading distance and could be considered 1X. Now someone with emmetropic but presbyopic vision (focused at infinity but no accommodation to focus closer like a younger person) will need a +10D (+10 diopter) lens (100mm focal length) to see at 10 inches. This is also about the strongest eyeglass Rx. A +40 diopter lens (25mm focal length) is about the strongest simple magnifier possible, and this lets you focus on items 1 inch away, which is in effect a 10X magnification from the standard 10 inches. But at +40D you are into loupe magnifiers and not eyeglasses. To have true magnification the lens system has to be away from your eye, not a contact lens with zero vertex distance or eyeglasses with a small vertex distance. This is why people with high-power prescription needs want to have small lenses that can tuck closer to the eye; then the world is not distorted bigger, just focused properly. A true simple magnifier produces a larger virtual image of the subject at infinity focus. But it has to be away from the eye to do so, otherwise you're just changing the refraction of your eyeball (and its focus point), not magnifying or minifying anything. Another way to think of this is to observe that putting a lens directly on top of an object doesn't magnify the object; a simple magnifier must be some distance in between both the object and the observer. If you really want things 2 feet away magnified by 3X, the device is called a "telescope" and is made of multiple elements. One example is the binocular scopes worn by surgeons and dentists, the simplest types being little Galilean opera glasses that are compact but dismal. Another is a stand-mounted operating microscope like a Zeiss OPMI (called a microscope when it actually is a close-focusing telescope). As a machinist you can improvise your own binocular "operating microscope" from a $10 pair of import roof-prism binoculars. All that is needed is to extend the travel of the eyepieces further back to bring the close focus point within a few feet: http://www.harborfreight.com/cpi/cta...emnumber=92442 |
OT, Zenni Optical help!
Ivan Vegvary writes:
I was hoping to find a bifocal that will allow me to do both with one set of glasses. Please advise. Like another follow-up post says, add 1.5D to the spherical Rx, and specify the bifocal adds to be 1.0D. Then you'll focus 2 feet straight ahead, and 16 inches down through the bifocals. |
OT, Zenni Optical help!
"Richard J Kinch" wrote in message . .. BQ340 writes: For example how would I specify a pair of bifocals that give my say 3X at 2'? Eyeglasses do not do that. Reader eyeglasses do not magnify per se; what they do is move the near point (how close you can hold something in focus) closer to your eye. The standard distance of 10 inches is considered normal closest reading distance and could be considered 1X. Now someone with emmetropic but presbyopic vision (focused at infinity but no accommodation to focus closer like a younger person) will need a +10D (+10 diopter) lens (100mm focal length) to see at 10 inches. This is also about the strongest eyeglass Rx. A +40 diopter lens (25mm focal length) is about the strongest simple magnifier possible, and this lets you focus on items 1 inch away, which is in effect a 10X magnification from the standard 10 inches. But at +40D you are into loupe magnifiers and not eyeglasses. To have true magnification the lens system has to be away from your eye, not a contact lens with zero vertex distance or eyeglasses with a small vertex distance. This is why people with high-power prescription needs want to have small lenses that can tuck closer to the eye; then the world is not distorted bigger, just focused properly. A true simple magnifier produces a larger virtual image of the subject at infinity focus. But it has to be away from the eye to do so, otherwise you're just changing the refraction of your eyeball (and its focus point), not magnifying or minifying anything. Another way to think of this is to observe that putting a lens directly on top of an object doesn't magnify the object; a simple magnifier must be some distance in between both the object and the observer. If you really want things 2 feet away magnified by 3X, the device is called a "telescope" and is made of multiple elements. One example is the binocular scopes worn by surgeons and dentists, the simplest types being little Galilean opera glasses that are compact but dismal. Another is a stand-mounted operating microscope like a Zeiss OPMI (called a microscope when it actually is a close-focusing telescope). As a machinist you can improvise your own binocular "operating microscope" from a $10 pair of import roof-prism binoculars. All that is needed is to extend the travel of the eyepieces further back to bring the close focus point within a few feet: http://www.harborfreight.com/cpi/cta...emnumber=92442 Richard, thanks for the great explanation. After reading it 4 times, I think I understand it. Isn't the internet wonderful? Thanks again for your wisdom. Ivan Vegvary |
OT, Zenni Optical help!
"Ivan Vegvary" wrote in message ... "Richard J Kinch" wrote in message . .. BQ340 writes: For example how would I specify a pair of bifocals that give my say 3X at 2'? Eyeglasses do not do that. Reader eyeglasses do not magnify per se; what they do is move the near point (how close you can hold something in focus) closer to your eye snip look for a special set of glassess called "maxTV" -- specifically these things: http://www.eschenbach.com/preview.php?pid=654 I bought a pair at Westec from Gesswein |
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