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  1. #11

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    Quote Originally Posted by Ed Sukach
    Quote Originally Posted by Lex Jenkins
    It's natural to see converging verticals with tall buildings. The eye expects it. By overcorrecting these lines from ground level using a shift lens or camera movements we create a perspective that doesn't exist in nature. It looks odd.
    True.

    The perspective "sensed" by the human eye is approximately equivalent to the image from a 100mm lens in the 35mm format, which translates to something like 160mm in 2 1/4 and ... whatever would be mathematically the same for 4" x 5" and 8" x 10" (Sunday morning and I haven't had breakfast yet). Everything is approxinmate, as no one yet has found a way to make accurate measurements of human perception.

    Any image taken with a lens *greatly* longer or shorter in focal length (tilts and swings not considered) results in an unnatural convergence of line and area scale... NOT to be confused with distortion (i.e., barrel, pincushion, or random abberation) - all lens - optical - errors.

    Never have I had to amke morecorrections to a message. I NEED coffee.
    Ed,

    That is interesting. I had always heard that the so called normal lenses (related to equivalent human vision) were those that were near the diagonal of the format. That would be near 50 mm for 35, 75 or 80 for 6X4.5, 150 for 4X5 and 300 for 8X10. I don't know where this "normal' designation came from. However, I don't know that I personally see the world at the 150 focal length in 6X 4.5, 300 mm length in 4X5, or 600 mm in 8X10 which is what your comment would indicate. That seems to be a fairly strong telephoto view. (It could be that maybe I am just not focused enough in my perceptions)...

    At any rate, explain further...I have a feeling that I am about to learn something here.
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

    Visit my website at http://www.donaldmillerphotography.com

  2. #12

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    At the risk of thread drift I'd consider my sense of vision - and by that I mean with my nekkid eyeballs - to be akin to a well corrected 17mm lens (for 35mm film format) with heavy spherical aberration.

    If that sounds peculiar, consider that most of use have very good peripheral vision that matches an ultrawide very closely. Yet we can only clearly see whatever we're actually looking at. Hence the reference to spherical aberration, which in a lens diminishes the clarity at the periphery of an image.

    Oddly enough, the photos I've seen over the past few years that seem to most closely mimic my sense of vision were illustrations in Shutterbug taken by Roger Hicks and Frances Shultz with their Alpa WA (which, I believe, stands for Wallet Annihilator) and 38mm Biogon (as in, "gone," referring to all of one's remaining money after buying the camera).
    Three degrees of separation from Kevin Bacon.

  3. #13
    Ed Sukach's Avatar
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    Quote Originally Posted by Lex Jenkins
    At the risk of thread drift I'd consider my sense of vision - and by that I mean with my nekkid eyeballs - to be akin to a well corrected 17mm lens (for 35mm film format) with heavy spherical aberration.
    If that sounds peculiar, consider that most of use have very good peripheral vision that matches an ultrawide very closely. Yet we can only clearly see whatever we're actually looking at. Hence the reference to spherical aberration, which in a lens diminishes the clarity at the periphery of an image.
    It doesn't sound "peculiar", but it would apply to "field of vision", not "perspective" within that field. That human central vision has more clarity is due to two major reasons; the distribution of rods and cones in the retina of the eye, and the ... I was about to write "psychlogical" .. but that is not quite correct ... uh... "Visual Preconditioning", where the information in the center of the visual field is more important, therefore we are conditioned to pay the most attention to it.

    Hmmm... "heavy spherical abberation" ... I don't think I have that in *my* vision... but I'm not sure I'd notice it if I did... the brain can correct all sorts of optical "strangeness" through experiencing and conditioning to make the end result "correct" ... perceptually correct.

    That the "normal" lens has a focal length equal to the length of the diagonal (or diameter) of the field is a more or less arbitrarilly choen value... at that focal length/ field diameter, quite a few optical design problems are minimized - that is why "Normal" lenses can have the largest maximum apertures.
    Carpe erratum!!

    Ed Sukach, FFP.

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