Which diopter?

Discussion in 'Leica and Rangefinders' started by abufletcher, Jan 10, 2005.

  1. Anyone have a quick 'n dirty way of guessing which diopter strength to use?
    For example, do camera diopter numbers have some rough relationship to
    those dime-store reading glasses with strengths like 1.5, 1.75, 2, etc.?

    Or can something be guessed by where I would set the diopter setting on an
    SLR with an adjustment slider/dial? For example, with my normal glasses, I
    have to move the slider on my D70's viewfinder almost all the way to the top.
    On the other hand, with the glasses I had made for computer work the slider is
    almost at the bottom. Would ZERO on the diopter scale be like putting the
    slider in the middle? If so, would UP be POSITIVE or NEGATIVE?
     
  2. Donald, do a search here on PN. In my few years of subscribing there have been at least two detailed threads on viewfinder correction lenses, containing expert advice from opticians.
     
  3. Jonathan, I tried a search but didn't turn up anything.
     
  4. I don't remember the means by which I figured it, but I was only
    able to narrow the calculation to 2 possible numbers. If you're
    talking about a diopter lens for a Leica M, I think the way to
    determine it with certainty is to look through each of the lenses
    and compare them. Positive is magnification.
     
  5. Going into a shop and looking at actual diopters on the camera is,
    unfortunately, not an option. Again what I'm looking for is some kind of quick
    and dirty way to get a rough handle on what sort of diopter is needed, i.e. a
    way to narrow the choices down to a minimum.

    For example, can someone tell me if shifting the diopter control UP on the
    D70 is positive or negative? If so, then since the diopter range is from -1.6 to
    +0.5 then the top position would be a +0.5 diopter.

    BTW, the viewfinder on the D70 appears slightly smaller with the diopter
    adjustment set to the top.
     
  6. Donald

    From my own experience the M cameras are .5 dioptre less than R cameras, eg:

    Leica R +2dioptre

    Leica M +1.5 dioptre

    These are the settings I use, but you, and your eyes, may need different settings.

    Regards

    Bruno
     
  7. There is no way to translate from an SLR to an M. SLRs may have some negative magnification built in, or may not.

    The drug store glasses diopter is the same as Leica diopter. There is a scientific definition for a diopter which I do not remember.

    The problem is few dealers carry the lenses. Tamarkin in New York does and were willing to exchange a few to get it right.

    Then your eyes change and you start again! Have your eye doctor give you your perscription and see how it changes. Make the correction lens change the same absolute amount.
     
  8. Donald, I've just tried the search too and can't find the threads I remember. I may have printed them out - will have a hunt.

    Meanwhile, here is what I remember of the discussion. Because the Leica M viewfinder is looking straight out into the world, the correction needed is that which enables your eyes to focus at infinity. Your optician should be able to quote this to you. Your focussing ability for close-distances is irrelevant. Thus I need reading glasses (only), but the M viewfinder is perfectly sharp (fortunate!).
     
  9. Donald

    Whoops! thought you were talking about Leica !

    regards

    Bruno
     
  10. I wear reading glasses (farsightedness.) If I buy those cheap drugstore glasses, I take
    something around +2.5 which fit my left eye okay but not so well my right which has
    stronger astygmatism. But that's another story. On my M7 (0.72) I can't focus at all with
    my naked right eye, and much better with my naked left eye. So I ordered a +1D
    correction lens for the VF. Now, I can focus with my right eye. It's not perfect (again, that's
    a problem with astygmatism, not farsightedness), but it's a big improvement. I also have
    +1D correction lenses on my Nikon SLRs (F2 and F3.) So, first, the diopter correction
    apparently is not the same as your reading glasses, probably because the VF already has a
    correction in it and the virtual image is formed at a different distance than the naked view.
    Two, I think negative diopter corrections are for nearsightedness, while positive are for
    farsightedness. Also, all the cameras I've had with built-in VF correction go from
    - something to +1, no more, though correction lenses have a more extended range on the
    plus side. Go figure.

    My $0.02.
     
  11. Oliver

    The R8 goes to +2, one of the reason I bought one.The R cameras seem to have very user friendly viewfinders.

    Regards

    Bruno
     
  12. No Leica, but early 50 eyes and an N80. Up is + diopter on the slider; it's marked. Without glasses I'm one click up. With my reading glasses (they are +) I have to move the slider all the way down, and it still doesn't look as good as no glasses with the slider properly adjusted. I suspect that +.5 would work for me (need to get a diopter for my FE2). But, SLRs are different than a RF; focus screen in a SLR is at some apperent viewing distance (I think around 1m) so I would imagine that a far sighted pseron would need less + correction with a RF than a SLR.
     
  13. I too notice that despite the references to the M finder being set at 2m, for me looking thru an M finder is the same as normal vision, i.e. I need one kind of correction to see far off objects and another for close up objects, thus rather than spend the dough on a diopter I just position my progressive-focal glasses so as to see sharply depending upon how far off the subject is. That, and thankfully with the rangefinder it isn't absolutely essential to see the finder 20/20 as it is with a reflex.
     
  14. For my M7 I have a +1.5 diopter. I have a
    distance prescription for glasses that is fairly mild,
    with magnification, just started needing it in the
    last 2-3 years. I walk around seeing distance pretty
    well without glasses, but if I really want to see in
    sharp focus, I've got to put them on. Maybe that info
    helps you to compare, or maybe you could contact Leica
    and ask them how their diopter #'s relate to your
    optometrist's prescription for you. I would think
    that you could mailorder 2 or 3 different lenses and
    return the ones that aren't optimum. I got my diopter
    from Cal's Camera in Costa Mesa Ca; maybe you could
    ask them about doing a mailorder.
     
  15. Ben Z wrote:

    <<....references to the M finder being set at 2m.....>>

    Surely that refers to the frame-lines, not the image plane of the viewfinder?
     
  16. Nope, it refers to the so-called "virtual distance" at which the finder is set (which seems applicable to SLRs with ground glass screens but not direct-view viewfinders). The framelines are set at the closest focusing distance of each focal length: 1.5m for the 135, 1 m for the 90 and 75, and .7 m for the others, minus some arbitrary amount Leica says will be hidden under a slide mount.
     
  17. From Dec 13, '04 - thread - M7 Diopter Guidelines. Spider's input at the bottom of the thread lays it all out:

    spider . , dec 14, 2004; 04:32 a.m.

    This may clear things up on the diopter issue:

    1) You are younger than about 45 and don't require glasses for distance or reading: No Leica diopter needed.

    2) Your distance vision is perfect:

    a) You are under 45. No Leica diopter needed, as the lens of your eye is able to make the correction for you to balance the M camera. The exception here will be in hyperopia (farsightedness), which is discussed below.

    b) For those over 45 who have perfect distance vision and do not have hyperopia: Although your distance vision is perfect, you likely require glasses for reading. In this case, your M camera makes things tougher for you by -0.6 diopter. Since the lens of your eye can no longer change shape to adjust for this -0.6 diopter, you may benefit by adding the +0.5 Leica diopter.

    3) You have myopia (nearsightedness) of more than -1.00 diopter: You likely wear glasses all the time to correct for your defective distance vision and therefore want to wear glasses while taking photos:

    a) If you are under 45, no Leica diopter needed.

    b) If you are over 45, you may benefit from the Leica +0.5 diopter to make the correction that the lens of your eye can no longer make. Essentially, your M camera is overcorrecting you by -0.6 diopter and you can't adjust for it because the lenses of your eyes have become stiff with age and can no longer change shape. This may cause eyestrain. The simple +0.5 Leica diopter may make a nice difference in your comfort. An alternative that I like is to have a pair of "compromise" glasses that undercorrects my nearsightedness by a half diopter. An example of this in my case is that I requir -2.50 glasses but I have a pair made up in -2.00. This gives me a little better close vision (I am over 40), while not compromising my distance vision much. When I put the camera to my eye the addition of the -0.6 of my M camera in combination with -2.00 glasses corrects my vision to very close to the -2.50 that I need to enjoy 20/20 vision.

    4) You have myopia of -1.00 diopter or less: You might not wear your glasses for most things because you see pretty well, however, you may wear them when you drive (especially at night). In this case you will probably be shooting without your glasses and might like having a Leica diopter to match your spherical correction. Choose the Leica diopter that most closely matches your prescription. -0.5 or -1.0 are available. Generally by the time you need -1.50 spectacles, you will likely be wearing glasses most of the time, including when you shoot. If you prefer not to wear glasses at -1.50, then a Leica diopter of -1.5 (if available) would very definitely help you do critical focusing with your M camera.

    5) You have astigmatism (cylinder on your glasses prescription) of greater than 0.5 to 1.0 diopter regardles of spherical correction: You probably should wear your glasses when you take photos. There is no Leica diopter to correct for astigmatism.

    6) You have hyperopia (farsightedness). As you get into your late 30's you may start to have trouble reading as, even though you could see like a hawk at distance when you were young (20/10 distance vision is not uncommon in young hyperopes) , your eye lenses are losing the ability to change shape to focus correcly on things near to you. Eventually you will likely require glasses for both distance and reading. Early into your transition into needing glasses but before you start to wear them, you will benefit for that period of time by using a +0.5, to +1.00 Leica diopter when you are shooting without glasses. Eventually you may go beyond this and will find that you are wearing glasses all the time and that your Leica diopter no longer works for you because you wear your glasses and shoot with them.

    With some exceptions based on personal preference and special requirements, there shouldn't a great need for Leica diopters of that go more negative than -2.00 or more positive than +2.00, as by the time you need this much correction, you likely are wearing glasses all the time. Of course there will be some people who do without glasses at 2.00 diopters, probably because of vanity, annoyance from spectacle frames, or desire to better see the framelines in the M, however, most people wear their glasses at this level of defective vision.
     
  18. I went through the same questions two years ago when I bought my M6ttl.

    My baseline was my Nikon F, for which I used a Nikon accessory diopter labeled +0.5. A Photonet poster told me the F comes from the factory -1.0, and that Nikon labels its accessory diopters based on the end result, not on the actual value of the diopter. Thus a Nikon +0.5 accessory diopter has actual value +1.5. You screw it in, and you're adding +1.5 to -1.0, yielding an end result of +0.5

    I called Leica. The rep said the M6 comes from the factory -0.5 and that Leica accessory diopters are labeled according to value added, not the end result. Thus, I bought a Leica accessory diopter from B&H labeled +1.0, yielding a net +0.5 (adding +1.0 to -0.5). The diopter did the trick.

    Further, I set my Nikon N75 one click from the top. The manual says the range is -1.5 to +0.8.

    I don't know how these relate to my eyeglass prescription.
     
  19. Ben Z, you've confused me. You seem to be saying that the Leica viewfinder image appears to the eye as an object at infinity (apart from that 0.6 dioptre), not as a close object. That was my understanding too, and seems to be the basis of Spider's truly helpful post reproduced above.

    The framelines, on the other hand, indicate the field of view (less a bit) at the closest focussing distance of each lens.

    Is that right, or not?
     
  20. Hello Donald.

    I use diopter lenses on M and R bodies. I use them with and without glasses at different
    times. I am shortsighted and have spectacles that are -2.25 for both eyes.

    With the R bodies I have added a -1.0 diopter lens. This gives an adjustment range from
    -3 to +1. If I set it for -2.5 I can see clearly with or without glasses. If I make the setting
    more positive than -2.5 I need to wear my glasses.

    The M6, M7 and MP bodies have a built in -0.5 dioptre. Don't know about the earlier
    models. So I add a -2.0 diopter lens and the viewfinder is clear without glasses, and with
    if needs be.

    An interesting thing for shortsighted people. With the correction lens installed on an M
    body it becomes very easy to focus with the right eye. The left eye's open view will be
    blurry and the right eye's view will be clear, seen through the corrected veiwfinder. The
    brain locks onto the clear view through the viewfinder. :)
     

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