Strange eye adjustment

Discussion in 'Darkroom Equipment' started by Mats_A, Jun 28, 2010.

  1. Mats_A

    Mats_A Member

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    Have noticed something that seems strange to me, not being an opthamologist.

    When I stand for a prolonged time in "complete" darkness my eyes seem to become more nearsighted. When I tray-develope a sheet I have an opaque divider between the tray and a timer with "glow in the dark" numbers. This is connected to a radio that will go silent when time is up.
    When I put out the light I can see the numbers very sharply but after about 4 minutes I notice that I have to lean closer to see the numbers. Just like being shortsighted.

    I would think that as the eyes adjust I would be able to see better in the dark, not worse.

    Anyone else noticed this?

    r

    Mats
     
  2. Ian Grant

    Ian Grant Subscriber

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    The dark shows up problems faster because you pupils have far less depth of field, also your eyes relax..

    It's why as your eyesight gets worse it becomes noticeable in low light levels. It's why people with failing sight & no glasses often use a bright light to read,, one of my friends uses a torch :D

    Ian
     
  3. holmburgers

    holmburgers Member

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    It could be that your iris was wide open, thus, shorter depth of field. I noticed once that in bright sunlight I could focus closer than ever before, presumably because my iris was so small and I had great DOF.

    Your eye is a lens, so the circle-of-confusion principles will apply just the same.

    update.... JINX! You have fast fingers Ian Grant
     
  4. richard ide

    richard ide Member

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    Slightly OT but a lot of people let their circle of confusion envelope their whole head. :D:D
     
  5. bsdunek

    bsdunek Subscriber

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    I resemble that!!!
     
  6. tkamiya

    tkamiya Member

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    Hey, my darkroom is a room of confusion.... my confusion is bigger than yours.
     
  7. phaedrus

    phaedrus Member

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    I'm an ophthalmologist, let me see through ;-)
    What you experienced is very common , it's called night myopia and constitutes a shift of up to -0.5 diopters at low light levels. Reason: the lens is aspheric, outer regions that get revealed when the pupil dilates have a shorter focal length. Plus, as has been mentioned, an increase of aberrations with a wide pupil.
     
  8. Poisson Du Jour

    Poisson Du Jour Member

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    Erm... well, that's interesting. Very interesting. A bit OT again for interest...
    How is it explained that I need glasses inside for reading/detail but can see perfectly well outside in most conditions, even for reading/writing — no specs necessary, amazingly. Is it the same as in the darkroom (though it's not dark in the house).
     
  9. phaedrus

    phaedrus Member

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    You're stopping down your eye when you go outside, smaller coc and so on. Break out your light meter, it IS darker in the house. Get a really strong reading light to equal the luminance you measure outside: presto, you can read again without glasses. But don't cheer too soon, this, too, will pass like all worldly things as presbyopia progresses.
     
  10. Wade D

    Wade D Member

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    I'm near sighted and can no longer see close up in near darkness. Even with glasses it's hard to drive at night. Astigmatism causes flare in oncoming headlights.
    I can't even read the date on a coin without a magnifier. Old age is fun isn't it. OK I'm not that old so call it middle aged.:wink:
     
  11. Bruce Watson

    Bruce Watson Member

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    And isn't this why testing defocus, astigmatism, etc. is done in a darkened room? To open up the iris, decrease DOF, and expose the aberrations?

    How dark is too dark? When do you cross over from being able to properly test for defocus to testing for night myopia? There's probably a line there somewhere (or at least a light level) that you want to approach but not cross, yes?
     
  12. Mats_A

    Mats_A Member

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    Thank you. This explains it. The things you can learn at APUG. Amazing!

    r

    Mats
     
  13. Poisson Du Jour

    Poisson Du Jour Member

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    Wow! Us humans have an expensive aspherical lens in our eyes. What are the odds it's made by Canon!?
    And which of the Five Aberrations of Seidel are most common with age? Mine is simply inability to focus closely (blur); easily corrected if I move back/put glasses on or as noted above, "odd" result in bright sun as opposed to inside. I have normal vision impairment for my age (my Mum at aged 94 has 3 sets of glasses, me just one). Others in my family (brother in law) have macular degeneration and another, niece, has astigmatism. I seem to do OK peering around and at detail in the darkroom with glasses on. But in another area, my move up to large format is impeded somewhat by my finding that it is much harder, not as straightforward or easy, to "detail" the ground glass than it is to manually focus on my EOS1N, which has both dioptric correction applied at the viewfinder and again at the magnifier (for critical manual focus of TS-E lens, which is not AF). Still, I'm not complaining what can be achieved with a personalised, accurate corrective facility. :smile:
     
  14. Sirius Glass

    Sirius Glass Subscriber

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    Old age is better than no age at all. Or on another subject, but you will see the parallel, my father used to complain about the dog's breathe, my brother would respond, "Bad breathe is better than no breathe at all."

    Steve
     
  15. Wade D

    Wade D Member

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    Very true! I'm getting by quite nicely at 56. A few focus aids and bad breath to boot.:D