Diopter correction v Reading glass stength

Discussion in 'Casual Photo Conversations' started by Ludmilla, Sep 20, 2021.

  1. My canon G5x mark ii has

    Eyepoint / Dioptre Correction
    Approx. 20 mm (from eyepiece lens centre)
    -3.0 to +1 m-1 (dioptre)

    What does this mean in terms of reading glasses magnification- I am currently on reading glass +2 but at max strength the canon viewfinder is not crystal clear.

    Is this because the viewfinder is poor or my reading glass strength is not strong enough.

  2. Ah, well, it all depends what baseline Canon are working from with their Dioptre correction factors.

    Almost no viewfinder places the focus at virtual infinity. They usually require the eye to focus at about 1 metre = ~ +1 Dioptre for someone with perfect eyesight. So adding the maximum built-in +1 correction theoretically takes you right up to your required +2 Dioptre reading glass strength. But these things aren't opthalmic prescription exact. You might need some + 0.5 Dioptre reading glasses as well as the camera's adjustment.

    If Canon have decided to place the 'neutral' focus at 1.5 metres instead of 1.0, then that could easily explain the discepency.

    FWIW, the EVF on my Sony MILC is the first viewfinder I've used with sufficient built-in adjustment to allow me to use it without spectacles (or contact lenses). Bless you Sony!
  3. Thanks RJ

    Is the Sony A7iv better than, say, the Sony A7c?
  4. By way of an example, this one from Nikon:
  5. Maybe I am too young to understand your issues, but if you can see well at infinity, adjust your camera to minus 1 and shoot without reading glasses?
    Hittingmyour optometrist tomdabble with their test glasses is always a good idea too.
  6. SCL


    Been thru this exercise too many times to count over the years with different cameras having their eyepiece set at different fractional diopters. Frustrating as Hell. But for me the usual solution, if I am wearing my eyeglasses is to use either a +/-0 or -0.5 diopter, especially after my recent eye surgery. My best advice, if you have a local camera dealer is to see if they have diopters or a test wheel to try - but decide in advance if you will shoot with or without glasses and base your decision on that baseline. I finally resolved my issues by finding a used diopter selector wheel o Ebay allowing me to self test what works for each camera - it's not perfect as it doesn't have all the fractional diopters, but some of them. Good luck and you should be delighted with the results once you get this sorted out.
    Jochen likes this.
  7. Dunno. Never looked through an A7c. Sorry. But it's miles better than the little A6000 that I have.
    Ludmilla likes this.
  8. Thanks, Jochen, that works for me although I am still unclear why - my fault not yours
  9. Here’s the diopter correction control. By putting the pointer in the centre I am assuming that equates to -1 (halfway between -3 and +1)

  10. The apparent distance of the screen in a Sony EVF is approximately one meter. Since my cataracts were replace, I can use the EVF without correction, which is consistent with a baseline +1.0 dioptre value. I have owned 6 models of a Sony, starting with an A7ii in 2014. All behaved in a similar manner, including an A9. A7iii, A7Riv and A7Siii in my current kit.
  11. Do not set the thing to a hypothetical, calculated value (the exact position of which unknown), when you can look through the thing while adjusting the dioptre.
    No glasses on. No lens on the camera. Look and set so the viewfinder screen is optimal in focus.
    If you cannot get it sharp, try again with glasses.
    But try! Do not guess.
  12. QG, sorry, my post wasn’t clear. What you suggest is exactly what I did.

    1. Wear No glasses
    2. Adjust the incredibly fiddly tool
    3. By trial & error, find the clearest view in the finder
    My post of the finder showed the results of my experiments coincide with Jochen’s suggestion.
    Last edited: Sep 22, 2021
  13. I owned the A6000 and had no trouble with viewfinder but my eyesight was better then- no reading glasses. But I must have made some adjustment to bring into the viewfinder into sharp focus.

    I always assumed the diopter correction was for people who wore glasses but I think, now, it’s for everyone- glasses or not. Is that correct?
  14. That's sort of how I did with my fuji as well except I did it with a lens and just focused on something about 10-20 feet away with the lens closed down enough that everything would be in focus from my selected spot to infinity, and then just adjusted the built-in diopter till my focal point and beyond were in focus. I guess you have to trust the auto focus on the camera, but it has seemed to work. I do it without glasses, so I take my glasses off to photograph. I've always found the glasses to really get in the way, so as the correction factor on my diopter, which doesn't have any numbers on it but Fuji's website states is –2 to +1 m–1. I use glasses that are a 2.0 and it seems to work great.
  15. I didn't realise this was such a difficult procedure, I've always just turned the adjuster in both directions until I find the clearest position. In my case with spectacles on (the only time I'm not wearing them is in bed or the shower). With my current Fuji camera I was finding the adjuster being moved presumably in and out of bags, a small piece of black tape has fixed this.
  16. It's best, or at least easier, to do it without lens, or with a very unfocused lens. You need to see the viewfinder image as sharp as possible, so set to markings in the viewfinder. Else you might confuse a misfocused lens with a badly set eyepiece correction.
    Last edited: Sep 22, 2021
  17. On an EVF camera, I bring up the menu and use that, easy to see when you've got it sharp.
  18. Good idea!
  19. What effect does using progressive eyeglasses have on this process?
  20. "Diopter" is a physical property of a lens, based on a practical use, which can be measured. Specifically, it is related to the distance a human eye or camera lens, focused at infinity, can focus on an object with use of a diopter lens or filter in reciprocal meters. In other words, a +1 diopter lets your eye focus at 1 meter, +2 diopter at 2 meters, etc. Minus diopters behave the same way regarding focal distance (i.e., for reading), but to correct for near-sightedness. It gets complicated because your eye and camera lens do not have a fixed focal distance. Furthermore, not every eye wil focus at infinity without aid, which is why many of us wear corrective glasses.

    That said, corrective lenses stronger than +/- 3 diopters are less common, so adjustable diopters in an eyepiece can often be used with the unaided eye. The problem wearing glasses is that you may not be able to see the entire field of view without moving your eye about. A higher eyepoint finder mitigates this problem. Most viewfinders, OVF or EVF, have a built-in +1.0 correction, which places the screen at an apparent distance of 1 meter.

    The accommodation of your eye makes it hard to focus accurately with an optical finder, because you can see through the ground glass and focus on a virtual image behind it. This is particularly true because as AF became common, the GG became more transparent for better viewing. Even manual cameras (i.e., Hasselblad) followed this trend with Acute-Matte screens. The solution is to focus your eye carefully on screen markings (or the Fresnel lines) when focusing the camera.

    You can't "see through" an EVF screen, but using it is more comfortable if you use the diopter adjustment so that screen markings (and the image) are sharp when you eye is relaxed. In any case, as Q.G. stated, it is not necessary to have an image, because the screen itself is the object of concern.

    On a personal note, I needed +1.25 glasses for far vision as I grew older. I could zero the viewfinder dial with glasses for convenience, but needed to dial up 1.25 diopters without them. After cataract surgery, my eyes are permanently focused for far vision, so the dial can be zeroed. Since my eyes are no longer "adjustable," that focus point is very clearly defined.

    An interesting "factoid" is that diopters are additive, so a +1.0 lens placed close to a +0.5 lens has the same strength as a single +1.5 lens. The concept of diopters was coined to make refractive measurements for corrective glasses simpler.

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