The Jazz Guitar Chord Dictionary
  1. #1

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    Hi,

    Simple question really: diopters correspond to lens focal length, so I suppose there must be a way to tie correction in diopters of reading glasses to the working range (I'm aware that depth of field decreases with focal length)?
    IOW, given that I know the correction of my reading glasses and the distance range over which they allow me to see in focus, can I determine how much more correction I need to put that range X cm closer - or, how that range shifts per added diopter?

    Should be basic highschool physics, in which case pointers to a succinct refresher are acceptable too

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  3. #2

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    Diopters are the reciprocal of focal length in meters. A 1 diopter lens will focus (ie converge parallel light rays passing through it) to a point 1 meter from the lens, a 2 at half a meter etc. Divide 1 by your desired focal length in meters to get the necessary lens power in diopters.

    But if that refractive power isn’t a match for your vision, it will not correct your reading vision well.

  4. #3

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    Well, that's the point, our eyes contain a focussing mechanism too which interacts. I've got a set of cheap readers with +1 correction, but I can't see sharp at 1m with them.

    I've got a set of spectacles for reading & computer work with which I can see sharp from a bit over 30cm to a bit over 50cm. I'd like to spec another pair for diy stuff, so closer.

  5. #4

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    Quote Originally Posted by RJVB
    Well, that's the point, our eyes contain a focussing mechanism too which interacts. I've got a set of cheap readers with +1 correction, but I can't see sharp at 1m with them.

    I've got a set of spectacles for reading & computer work with which I can see sharp from a bit over 30cm to a bit over 50cm. I'd like to spec another pair for diy stuff, so closer.
    The simple truth is that you can't do that with static corrective lenses. As your need for close range correction increases, you'll be moving closer to the page. But there are some adjustable focus lenses that use mechanical, LCD, and other technology to let you dial in a compromise between clarity and focal distance that suits you best. They have a little knobs on them and you adjust them yourself. Google "adjustable focus eyeglasses" and you'll find many available.

    You'll get the same effect by having readers with different corrections. If you need 3s for perfect reading, 1.5s will give you longer distance but less sharpness. Going to a 2 will bring you closer to the page with better clarity, etc. You just have to find the minimum level of clarity that's acceptable to you and live with the distance. The more light you have on the page, the better your close vision will be because it makes the iris close down. This covers the periphera of the lens, and that's the most curved part. The center is the flattest, so you need less correction when looking through the middle of the lens of your eye. But you need bright light to keep the iris over the curved outer region.

    I'm still on 2.25 readers and doing fine. I do have a bit of trouble reading charts on the keyboard's lyre where I play regularly because it sits on top of the Hammond and is too far away. Adjustables might be what you want. I suspect that compromising clarity of focus for distance is not an acceptable trade-off for most people, and some of the charts that vocalists bring to us are barely readable by a teenager with perfect vision anyway

  6. #5

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    If you can see comfortably with a +2.50 OTC reader at 16” then theoretically a +1.25 OTC reader will allow you to see comfortably at 32”. Of course there are other variables but that is the basic math of it.

    You might inquire about midrange “progressive” type lenses. For example; Shamir Smart Office™ - Shamir Lens Technologies

    Many of my clients enjoy the wide field of view these lenses offer for computer and reading tasks including reading music. The lenses maximum viewing distance is around 10 feet so don’t try driving with them. Consult with your eyecare pro for more details.

  7. #6

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    Quote Originally Posted by Bflat
    If you can see comfortably with a +2.50 OTC reader at 16” then theoretically a +1.25 OTC reader will allow you to see comfortably at 32”. Of course there are other variables but that is the basic math of it.
    OK, that's simple indeed, and exactly what I was looking for. Thanks!


    I've got a pair of multi-focals which cost me a rib or two and which I barely use because the reading part is rarely at the right location. Most of the time I'm not wearing any glasses at all at the moment. The boon of being myopic is that I have good close-by vision without any correction, but not at the same range in both eyes (IIRC my current dedicated readers are -0.25 and +0.75). Not that long ago I walked around at home with my for-far glasses on my nose, with a fitting pair of generic readers either perched on top or at the appropriate position in front of them. I stopped doing that only because I got fed up with the weight and having to clean 2 sets of glasses; otherwise it was a perfect solution for me.

  8. #7

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    Im surprised no one brought up the A word. Do you know if you have any Astigmatism?
    I do in one eye, no store bought reader can ever be clear in the eye as they of course offer no correction. My go to music readers had to be made with the correction in the lens.
    Mentioning it as it frustrated me at first, getting store readers and never getting satisfactory results.
    Best of luck!
    jk

  9. #8

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    I do, in one eye, but it is so tiny that it can remain non-corrected. I only notice it when not wearing any glasses when I've been wearing glasses that do have the "cylinder".

    Store-bought readers always have 2 identical lenses so I'm looking at ordering a pair from on only optician anyway.