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  1. #11

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    Quote Originally Posted by phaedrus View Post
    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.
    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?
    Bruce Watson
    AchromaticArts.com

  2. #12
    Mats_A's Avatar
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    Quote Originally Posted by phaedrus View Post
    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.
    Thank you. This explains it. The things you can learn at APUG. Amazing!

    r

    Mats
    Digital is for communication, film is for documentation.


    http://www.flickr.com/photos/studiopirilo

  3. #13
    Poisson Du Jour's Avatar
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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.
    “The photographer must determine how he wants the finished print to look before he exposes the negative.
    Before releasing the shutter, he must seek 'the flame of recognition,' a sense that the picture would reveal
    the greater mystery of things...more clearly than the eyes see."
    ~Edward Weston, 1922.

  4. #14
    Sirius Glass's Avatar
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    Quote Originally Posted by Wade D View Post
    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.
    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
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  5. #15
    Wade D's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    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
    Very true! I'm getting by quite nicely at 56. A few focus aids and bad breath to boot.

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