How to determine correct diopter?

Discussion in 'Leica and Rangefinders' started by scott squire / nonfiction media, Jun 13, 2003.

  1. So I wear (nearsight) correction glasses, most of the time. Often
    leave them off when shooting. I'd like to make the most of the
    viewfinder, so how do I determine which (if any) would be the
    correct diopter?
    Cheers,
     
  2. The only real way to get a correct fit is to go to a Leica Dealer and try the ones nearest your prescription in your camera model's viewfinder. If you're not near a Leica dealer, then you may have to (1) find out your prescription's plus (+) or minus (-) diopter value and then (2) order several from a dealer with the understanding that you can return the ones that don't match your prescription.
     
  3. The last time we got into this, a couple of years ago, it was pointed out that the finder image is presented at a virtual distance of two meters; and that there is some negative diopter correction (trusting my failing memory, I think 1/2 diopter was mentioned) already in the finder. In some way this influences the choice of correction lens you need (I think it does). I don't remember whether it was said that the lens supplied with the camera comes out when you install the new diopter; or if you take the 1/2 diopter figure into account when ordering your personal corrective diopter.

    The point being, don't run right out and do anything until a couple of the members who really have this down pat get a chance to respond to this. There is something specific you're supposed to know.
     
  4. Actually, I'm going in for an eye exam next week, and I will simply take an M body along and request that I be measured through the camera, for the best lens correction for my glasses and contacts.

    One problem with using corrective lenses, I guess, is that one would have to be constantly putting on and taking off one's eyeglasses, unless the prescription is mild enough to get away without wearing them much of the time. I like to wear contacts for serious shooting, but then at my age I have to put on the 1/2 frame reading glasses to see the camera controls. It's a good argument for shooting my R5, which displays everything in the finder.
     
  5. I got tired of the glasses routine and had lasik in January. It's about the price of a M7 and can't correct for tired old eyes (still nead readers). But it's wonderful after 45+ years of glasses to be able to use a viewfinder without diopters or giving up real estate to the distance imposed by glasses.

    Yes, you can get lasik for less than the price of an M7 but consider the concept of "discount eye surgery" before jumping in.
     
  6. I'm an eyeglass wearer and at my last eye exam, I asked the optician for a prescription for the diopter correction lenses to by used on my cameras. He seemed entirely familiar with this.

    So far, I've only used the prescription for one camera, a Fuji GS690II, which uses the Nikkor diopter lenses. His prescription seems to be right on the money.
     
  7. <<So I wear (nearsight) correction glasses, most of the time. Often leave them off when shooting. I'd like to make the most of the viewfinder, so how do I determine which (if any) would be the correct diopter>>

    If you do not have astigmatism in your shooting eye, and you do not need bifocals to see clearly at 2m (about 6ft) you want the Leica diopter that is the closest to your distance Rx. If you have astigmatism (but again, don't need bifocals for 2m) you want the diopter that is 1 diopter stronger than your distance Rx (more negative, ie -3 if your Rx is -2). Optometrists/opthalmologists refer to this as the "spherical equivalent".

    If you have no astigmatism, but do need bifocals for 2m, you want to know from your eye doctor what the "add" is for you at 2m...and then add that to your distance Rx. Eg: If your Rx is -3 with a +1.5 "add" for correction at 2m, you get the Leica diopter of -1.5.

    Same scenario as above, but with astigmatism: again, one diopter more negative. In the example, you'd need a -2.5 diopter.
     
  8. Scott
    I hope my recent experience may be of some use to you.

    Being long sited I only wear glasses for reading and close up use, and my cameras (R8 & MP) being very ergonomic and intuative to use allow me most of the time to feel my way around with out even looking. Of course the R8 shows everthing in the viewfinder, which I have set to +2 dioptre. With the M camera the optical system of the viewfinder seems to be somewhat different, in that although I have read that there is a -0.5 dioptre built in, I can JUST ABOUT get away without a correction lens fitted, but when I did get one I found that a +1.5 dioptre was ok! Very odd but that is what I found out to be the power needed.

    Therefore I suppose you just have to experiment with various strengths until you can see clearly.

    Good luck.

    Bruno
     
  9. Best and easiest solution is to go into a camera store that's got the diopter lenses you can try. My distance prescription is 1.25, not sure if I have astigmatism or not, but I ended up choosing 1.50 for best viewing for distance with my M.
     
  10. WOW, you guys, absolute tonne of great answers, thanks. I'll
    investigate first the calling of the optometrist who prescribed my
    eyeglasses, then the fiddling with bits and the nice camera
    man's counter.

    Cheers,
     
  11. Your optician's prescription isn't necessarily applicable to the Leica. My prescription is +4.75 which, of course, Leica don't make so I thought I was stuck with using my left eye and getting a squashed nose (OK, I get that on my SLRs anyway).

    Luckily, I found a +3 on eBay for well under half price, screwed it in (after I realised you don't unscrew the viewfinder lens first!) and it worked perfectly. So as others have said, best try before you buy.
     
  12. Harvey is correct. i went through this last year with the M7, the
    ophthalmologist's refraction is simply a starting point for you. Go
    to the store and try the said corrective lens as well as those 0.25
    diopters above and below. Look at a sign 2 to 3 meters away
    and see which one results in the sharpest focus.
     
  13. what you want is the diopteric correction closest to your spherical equivalent. if you do not have astigmatism, this is equal to your distance refraction.

    if you do have asigmatism, the spherical equivalent is equal to 1/2 the astigmatism correction added to the spherical component of the prescription. for example, if your correction is -3.00 (sphere) +1.00 (cylinder, or astigmatic correction...which is specified as being oriented to a specific axis on your eyeglass prescription), your spherical equivalent is -3.00 plus +1.00/2 = -2.50. if your prescription was -4.50 +2.00 (at specified axis), your spherical equivalent would be -3.50.



    you want to get the eyepiece closest to your spherical equivalent.
    keep in mind that optometrists usually write prescriptions in minus cylinders, while ophthalmologists usually write prescriptions in plus cylinders. the spherical equivalent is still the sum of 1/2 the cylinder added to the sphere. the axis is irrelevant in calculating the spherical equivalent.

    if your spherical equivalent is -2.50 and you use bifocals, i would use the -2.00 eyepiece, since you will be slightly undercorrected for distance, but more in focus at near. if your spherical equivalent is +1.50 (and you use bifocals), i would use the +2.00 eyepiece. this is a somewhat complicated concept to explain fully in a short thread since myopia, hyperopia, and astigmatism, with or without presbyopia may be involved in any individual's prescription.

    if you want to email me your prescription, i will be happy to make a recommendation.

    i am familiar with this topic since in my day job i am an ophthalmologist.
     
  14. leica has said me: you must know the diopter required at infinity,for me + 1 , and not correction for reading, for me +2,5, than leica wiewfinder is -0.5 .the correct lens for me is -0,5.
    also for others amnufactors is the same. konika exar rf is basic 01, the right lens is 0.
    pentax basic is 0, the right lens is +1
     
  15. Searching for the correct diopter is not an easy task. We are talking about a reference of not only your prescription, but the additional variable (which is exponential) in conjunction with the viewfinder. I had the same problem until I found an optician in Shanghai who is a Leica M user and knows exactly the innards of the M viewfinder (which is fairly complicated by itself with optics and lens). He computed my prescription and custom made an eyepiece for me. It's a wonderful piece of work. The problem now is I wanted several of these so that I can attach one to all my cameras, but he is so busy. Now I find myself in an awkward situation of liking just one camera because of the eyepiece attachment and it cannot be easily swapped to all my other Leica bodies.
     

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