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Lens Correction vs Distance/Focal Length
Old 07-16-2017, 06:07 PM   #1
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Lens Correction vs Distance/Focal Length

If someone had a +2.25 correction for reading and a +1.00 correction for distance, how would she determine the best correction for an object 3.5 to 5 feet away? I could interpolate, but I don't know what distance is associated with the +1.00 correction, or if it's a linear relationship. I could resort to trial and error but I thought I'd ask here. I haven't found the right words with Google to yield an answer.
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Old 07-16-2017, 08:41 PM   #2
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I am close to those numbers myself and use some +1.50 for computer use. These used to be my up close reading glasses years ago and now are my computer glasses. With maturity comes presbyopia, a medical term that means your arms get shorter with age.
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Old 07-16-2017, 09:32 PM   #3
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If someone had a +2.25 correction for reading and a +1.00 correction for distance, how would she determine the best correction for an object 3.5 to 5 feet away? I could interpolate, but I don't know what distance is associated with the +1.00 correction, or if it's a linear relationship. I could resort to trial and error but I thought I'd ask here. I haven't found the right words with Google to yield an answer.
Hahahah, you kidding right? Id say an eye Dr might be the definitive source for this one.
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Old 07-17-2017, 05:16 AM   #4
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This is why progressive lenses are so nice, for those of us who can tolerate them.
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Old 07-17-2017, 05:35 AM   #5
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I have +3.00 and +1.25 monovision contacts. I have no idea what perfect for 3.5 - 5 feet but just looking around the room it seems like my 1.25 eyes are darn good at that distance. My reading eye is goo for computers and books but falls off rapidly around 2 feet.
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Old 07-17-2017, 06:22 AM   #6
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This is why progressive lenses are so nice, for those of us who can tolerate them.
Yep. Love em. I'm -4.25 long & -2.00 for reading.
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Old 07-17-2017, 07:57 AM   #7
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This is why progressive lenses are so nice, for those of us who can tolerate them.
I have progressives and they're OK for general use, but not my specific use (seeing a golf ball as clearly as possible at address). +1.00 is not enough and +2.25 is too much. If push comes to shove, I'll just try various cheaters in hopes of finding the right correction. I have some old +1.25 glasses to try already.
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Old 07-17-2017, 08:46 AM   #8
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Actually, it's pretty simple and linear. For a given distance prescription, diopters are added for closer vision. For example, my "add" for close vision is 2 diopters. For mid distance/trifocals I use half of this or 1 diopter. For me this works great for computer use and airplane instrument panels. In fact, every time my prescription changes I order single-vision glasses from China with the full "add" for reading and half the "add" for computer. On sale and not being picky about frames I often get them at two for $25. So I have pairs sitting everywhere that I read and at my two computer monitors. For a little more distance, like the front sight of a rifle or a pistol held at arm's length I use a supplemental 0.75 diopter lens similar to this one: https://www.magnifyingaids.com/Bausc...lass-magnifier.

My guess is that for your 3.5-5 feet, 1/2 or 3/4 diopter will be the answer.

I also have clip-on glasses at +1.5 and +3 diopters. I use these for close work like gunsmithing and machining. (Like these: https://www.amazon.com/Carson-Optica.../dp/B001FADHG8)

But you really don't have to worry about all this distance and numbers stuff. Just buy a cheap pair of +.75 or +.5 reading glasses and "wear" them on top of your regular glasses. Then see if you have the needed focus point. If not, add or subtract power until you have what you like.
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Old 07-17-2017, 08:53 AM   #9
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Actually, it's pretty simple and linear.
That may not be true for everyone.
My perfect reading correction is 2.25 but it's 1.75 for the computer.
Your Magnification May Vary.
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Old 07-17-2017, 09:26 AM   #10
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That may not be true for everyone.
My perfect reading correction is 2.25 but it's 1.75 for the computer.
Your Magnification May Vary.
It depends on the computer screen distance and your normal reading distance. Your optician is correcting for a computer screen distance that is not terribly far from your reading distance. My computer distance is about 24" and half my "add" works pretty well. For a tablet/laptop screen read from a closer distance, I actually use my reading correction.

To the extent people need to focus at different distances, the magnification "add" will change. Bur for a given distance it will always be the same number. That's why I suggested to the OP that she just experiment a little rather than going nuts with the arithmetic.
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Old 07-17-2017, 09:39 AM   #11
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I suspect +1.25, +1.50 or +1.75 will be best for me at 3-5 feet. I'll try all three. Just wondered if I could calculate the correction instead of trial and error. Thanks!
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Old 07-17-2017, 09:41 AM   #12
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I have progressives and they're OK for general use, but not my specific use (seeing a golf ball as clearly as possible at address). +1.00 is not enough and +2.25 is too much. If push comes to shove, I'll just try various cheaters in hopes of finding the right correction. I have some old +1.25 glasses to try already.
That is what I did after my cataract surgery, since I had no idea what strength of readers I needed. I went to Walgreens and tried on various strengths. Once I had it narrowed down to the approximate strength, I went to Amazon and ordered a set of 1.5x and another of 1.75x. Amazon had them at 3 pairs for $4.50 with free Prime shipping:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

After a week or two of using both strengths at home, I decided that 1.5x was best for my purposes and ordered a nicer pair at that strength (which is what I am wearing right now).

It is great to have 6 pairs of left over cheap readers, though, because I have them all over my house and I am never far from reading glasses. They are perfectly usable.
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Old 07-17-2017, 09:50 AM   #13
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It is great to have 6 pairs of left over cheap readers, though, because I have them all over my house and I am never far from reading glasses. They are perfectly usable.
+1, I resemble that remark. I have cheapo cheaters in my car, in DW's car, by my family room chair, in my sail bag, in my golf bag, on my workbench, at my desktop PC, and in the kitchen. Plus two pairs of progressives in plain & sunglasses, bifocal sunglasses and several pairs of non-prescription sunglasses.

Getting old isn't for (forgetful, vision impaired) sissies...
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Old 07-17-2017, 10:01 AM   #14
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+1, I resemble that remark. I have cheapo cheaters in my car, in DW's car, by my family room chair, in my sail bag, in my golf bag, on my workbench, at my desktop PC, and in the kitchen. Plus two pairs of progressives in plain & sunglasses, bifocal sunglasses and several pairs of non-prescription sunglasses.

Getting old isn't for (forgetful, vision impaired) sissies...
Oh, oops! I didn't realize that you already have lots of cheapo cheaters.

Like you, I have them all over the place. I also have a pair on the bedside table and another in my purse. And, I have a spare pair of readers right here by the computer, just in case I misplace my nicer ones.

I do like the fact that readers are so cheap. Before my cataract surgery, my (trifocal) glasses cost a lot more.
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Old 07-17-2017, 11:43 AM   #15
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Whatever you do, try to be more efficient than this woman:

Surgeons remove 27 contact lenses from woman's eye
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Old 07-17-2017, 12:23 PM   #16
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Whatever you do, try to be more efficient than this woman:

Surgeons remove 27 contact lenses from woman's eye
Before my cataract surgery, I had (and LOVED) contacts. I can understand where she is coming from! Though, I never did what she did.

Eventually I had to quit wearing them due to over-wearing syndrome, which I guess is minor corneal damage. I went back to just plain old ugly glasses. That's me, "Four Eyes"...

Since my cataract surgery, I don't have to wear glasses at all except up close! This is great. I can walk and drive with no glasses whatsoever. It's like being a kid again.
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