explanation needed for optical illusion in digital photo

Discussion in 'Digital Photography' started by Eigenvector, Jul 29, 2003.

  1. Eigenvector

    Eigenvector Guest

    This may or may not be the best place for this question, but it came to me
    as I was trying to photograph the moon. I got the shot okay, nice and clear
    and properly lighted but it looked so small!

    Can anyone give me a good solid explanation for why objects in my digital
    camera appear so small compared to what I see with my eye? I (no pun
    intended) was expecting to have my shots turn out to be identical to what I
    was seeing but when the camera displayed them it was like I took the shot
    from 50 miles away. Why do cameras in general display the objects in
    question so much smaller that what the photographer sees when he takes the
    shot.

    http://photos.imageevent.com/eigenvector/blethemlake/large/P7160643.jpg

    That is a representative shot - full 8x zoom, in reality that mountain is
    huge from that spot, but in the shot it looked dinky.

    http://photos.imageevent.com/eigenvector/blethemlake/large/P7160644.jpg

    Here is the unzoomed version.
     
    Eigenvector, Jul 29, 2003
    #1
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  2. Eigenvector

    gr Guest

    The brain likes to play tricks with distant objects like the moon (and
    mountains, etc.), especially when it's close to the horizon or there's some
    other reference to view it against. The brain makes them look bigger than
    they really are. The moon is about 0.5 degrees in diameter (give or take a
    smidge), no matter where it is in the sky... high or low. But when it's low,
    we see it as bigger than it really is. Our brain says that any distant
    object visible must be really big, so we see it that way.

    Here's a way to partially "untrick" your brain. Bend right over and put your
    head upside down and between your legs. Then, look at the full moon as it
    rises over the horizon. Note that it doesn't look so big any more, because
    your brain doesn't have a good reference to place it against. (At least I
    hope you don't normally go around bent over with your head between your
    legs...)
     
    gr, Jul 29, 2003
    #2
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  3. Eigenvector

    Charlie D Guest

    Anyone watching you would see the moon too. ;)
     
    Charlie D, Jul 29, 2003
    #3
  4. Eigenvector

    gr Guest

    :) Yeah, it's best not to do it in a public park.
     
    gr, Jul 29, 2003
    #4
  5. You got closer than 50 miles from the moon?

    Sorry, I couldn't resist.



    Rodney Myrvaagnes J36 Gjo/a


    "In this house we _obey_ the laws of thermodynamics." --Homer Simpson
     
    Rodney Myrvaagnes, Jul 29, 2003
    #5
  6. Eigenvector

    Don Stauffer Guest

    These 'illusions' have been much discussed in the professional
    (psycho-physics) literature, and I have never seen a good explanation.

    However, keep in mind that what the brain perceives is not at all what
    is on the back of the retina. Much of the effect you mention appears to
    be an 'attention' related effect.

    Eye is highly distorting, brain remaps. Brain sees different estimate
    of horizontal angles than vertical ones. Retinal image is sharp only in
    center degree or less of angle, very fuzzy at edges, but brain makes it
    appear that resolution at edges is same as center. A full list of these
    effects is very long.

    I would say it is only the way our visual cortex is 'programmed.' There
    is no physics explanation.
     
    Don Stauffer, Jul 29, 2003
    #6
  7. Eigenvector

    Dave Balcom Guest

    }It is a mental illusion, more than an optical illusion.

    I vaguely remember from school that the reason the moon appears
    larger/orangish at the horizon is because the atmosphere is thicker
    (between the moon and the observer). The added air means added
    refraction. BTW, the sun shows the same effect at sunset/sunrise and
    is for all practical matters the same apparent size as the moon...
     
    Dave Balcom, Jul 29, 2003
    #7
  8. Eigenvector

    gr Guest

    I suggest you get out a telescope and measure the angular size of the moon
    yourself, both near the horizon and overhead. (Do it the same night, so as
    not to get minor size differences due to the moon's proximity to Earth.)
    You'll find the size difference imperceptible. So, as you like to say,
    BZZZZZZZZZZZZTTTTTTT!!!!!!
    WRONG!
     
    gr, Jul 29, 2003
    #8
  9. Eigenvector

    George Kerby Guest

    DAMN!
    I'm going to find my high school science instructor and kick his old
    shrivvled-up ass!
    I stand corrected, but it sounded reasonable.
    DING_DING_DING: A WINNER!
    http://unmuseum.mus.pa.us/exmoon.htm
    And for those of us who need visual stimuli:
    http://antwrp.gsfc.nasa.gov/apod/ap020130.html

    It seems that this phenomenon is widely debatable, but water doesn't figure
    in the equation.


    ______________________________________________________________________
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    George Kerby, Jul 29, 2003
    #9
  10. Eigenvector

    John M Guest

    LOL I just love it when people are so convinced they know what they are
    talking about, when they actually have no clue... Water has a magnification
    factor of 1.4X?? Where in the hell did you hear that one?
     
    John M, Jul 29, 2003
    #10
  11. Eigenvector

    ralford Guest

    you will also remember from school that the refracted apparent size would
    also manifest itself on film/ccd. It doesn't.

    refraction doesn't explain the illusion.

    cheers,

    rma
     
    ralford, Jul 29, 2003
    #11
  12. Eigenvector

    Mxsmanic Guest

    This is incorrect. Measure the size of the moon in both positions
    through a telescope or other optical device with a measurement grid, and
    you'll see. It is always the same size.
     
    Mxsmanic, Jul 29, 2003
    #12
  13. Eigenvector

    Eigenvector Guest

    Thank you all for the replies. I didn't want this thread to turn into an
    argument over why the moon appears larger than it is. I've seen those
    arguments and have come to the conclusion that we simply don't know yet.
    But back to the original question which was really on why photographs make
    objects appear so small. I appreciate your answers, thank you mxsmanic for
    clarifying the notion around wide angle and narrow angle lenses. I guess
    the better question would be to go to an optometrist group and ask them what
    is it my eye/brain does to the incoming light image.
     
    Eigenvector, Jul 30, 2003
    #13
  14. Eigenvector

    Charlie D Guest

    Charlie D, Jul 30, 2003
    #14
  15. A perfect exampe of this is a street in my community which terminates at a
    harbor. The distance across is about 5 miles. When you make the final turn
    down the street you see a straightaway which ends with a view of the water
    framed by houses along both sides, very similar to your example. With just
    water is looks quite normal but if there happens to be a ship in the view, as
    you make the turn from about 3/4 mile from the water, the ship looks like it's
    anchored alongside the waterfront! But by the time you get to the end of the
    street the ships has "shrunk" and you can see that it is really about 4 miles
    out.

    It's all about relative sizes and distances fooling your perception. Sme
    reason the settign sun/moon look so large.

    Glenn
     
    Glenn Woodell, Jul 30, 2003
    #15
  16. It places more emphasis on the central area of your vision. You still see the
    periphery just as you do the central part but you don't pay as much attention
    to it. When you create a 2D image and look at it you generally scan over the
    entire image rather than scan with the viewfinder which changes your framed
    view as you move.

    Glenn
     
    Glenn Woodell, Jul 30, 2003
    #16
  17. Eigenvector

    ralford Guest

    There are a couple of classic optical illusion examples that demonstrate
    this phenomenon. One is the two partial thick quarter circles that appear
    different sizes when placed one above the other - most older than 30 will
    have seen this? Another example, closely related to this discussion, is
    found at http://www.eyetricks.com/0502.htm

    cheers,
    rma
     
    ralford, Jul 30, 2003
    #17
  18. Eigenvector

    Browntimdc Guest

    Here's a thought to ponder: If it were true that some atmospheric effect
    made the moon look bigger near the horizon then the wedge shaped slice of
    air would make the moon look elliptical, not just larger.

    Tim
     
    Browntimdc, Jul 30, 2003
    #18
  19. Eigenvector

    Mxsmanic Guest

    Photographers use this trick all the time; that's the purpose behind
    wide-angle and telephoto lenses. I'm surprised that they need it
    explained to them.
     
    Mxsmanic, Jul 30, 2003
    #19
  20. Eigenvector

    Eigenvector Guest

    I'd always wondered how haze was filtered out of photographs. That's a huge
    problem with most of my outdoor shots, the haze is a serious problem. That
    was another part of my basic question, but I hesitated to ask. Why doesn't
    my eye see the haze, yet the camera is almost obscured with it. Sounds like
    the camera needs to have the incoming light filtered.
     
    Eigenvector, Jul 31, 2003
    #20
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