EOS 300 DOF preview? huh?

Discussion in 'Digital Photography' started by [blu|shark], Jan 15, 2004.

  1. [blu|shark]

    [blu|shark] Guest

    i seem to fail to understand how _depth of field preview_ button on Canon
    EOS 300D works. manual lacks a thorough explanation, and when i use the
    button (in one of the creative modes), i don't notice any difference.
    i use 3.5AV thinking it should maximize the effect, but nothing really
    happens. (at least nothing i notice)

    i'd appreciate a few words of explanation on this subject, and also a tip
    on whether i should hold the button or just press it when i use it :)

    thank you!
    Matija

    --
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    [blu|shark], Jan 15, 2004
    #1
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  2. [blu|shark]

    Chris Brown Guest

    In article <1017l0mjcbzff$.1q78q5ls7d9lo$>,
    [blu|shark] <> wrote:
    >i seem to fail to understand how _depth of field preview_ button on Canon
    >EOS 300D works. manual lacks a thorough explanation, and when i use the
    >button (in one of the creative modes), i don't notice any difference.
    >i use 3.5AV thinking it should maximize the effect, but nothing really
    >happens. (at least nothing i notice)


    The DoF preview button simply closes the aperture to your selected value,
    for as long as you hold it.

    If the lens is set wide-ppen anyway, it won't do anything. Try setting the
    aperture to f/16, press and hold the button, and notice what happens.
     
    Chris Brown, Jan 15, 2004
    #2
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  3. [blu|shark]

    cc Guest

    This is a feature I have been hoping for ever since my Olympus SLR's
    shutter broke (Olympus were the only brand to have DOF preview for a
    while). I'm very glad to have it again on my 10D. What it does is allows
    you to view what will be in focus or appear sharp when the lens is
    stopped down to the aperture (f-stop) that you have selected. When you
    are looking through the viewfinder and not pressing the DOF preview
    button the lens is wide open and thus there is a very small depth of
    field (only a thin plane is in focus). If you increase the f stop value
    the DOF range will increase (more stuff will appear sharp), and pressing
    the button will allow you to see this effect and see what will actually
    be sharp in your picture. If you have set the aperture at its widest
    (lowest number) the button will make no difference. If you press the
    button when the f-stop is set to a higher number (smaller aperture) what
    you see through the viewfinder will become darker and you will see that
    more of a distance range is sharp.

    [blu|shark] wrote:
    > i seem to fail to understand how _depth of field preview_ button on Canon
    > EOS 300D works. manual lacks a thorough explanation, and when i use the
    > button (in one of the creative modes), i don't notice any difference.
    > i use 3.5AV thinking it should maximize the effect, but nothing really
    > happens. (at least nothing i notice)
    >
    > i'd appreciate a few words of explanation on this subject, and also a tip
    > on whether i should hold the button or just press it when i use it :)
    >
    > thank you!
    > Matija
    >
     
    cc, Jan 15, 2004
    #3
  4. On Thu, 15 Jan 2004 16:08:36 +0100, [blu|shark] wrote:

    > i seem to fail to understand how _depth of field preview_ button on Canon
    > EOS 300D works. manual lacks a thorough explanation, and when i use the
    > button (in one of the creative modes), i don't notice any difference. i
    > use 3.5AV thinking it should maximize the effect, but nothing really
    > happens. (at least nothing i notice)
    >
    > i'd appreciate a few words of explanation on this subject, and also a tip
    > on whether i should hold the button or just press it when i use it :)


    Autofocus systems always operate with the lens aperture fully open. So,
    when you focus on something, you will be using the lens at maximum
    aperture, but when the shot is actually taken, the aperture stops down to
    the selected value.

    To see the effect of DOF preview clearly, set the camera to Av, choose an
    aperture of f/16 or f/22, pick s subject to focus on, half press the
    shutter, and then depress the DOF preview. By using f/3.5, which is the
    max aperture on the 300D's kit lens, you won't see anything.

    You will see the viewfinder image become substantially darker, as the
    aperture stops down, and the depth of field visible in the viewfinder will
    visibly enlarge.

    HTH,

    Mike.
     
    Mike Brodbelt, Jan 15, 2004
    #4
  5. [blu|shark]

    Jim Townsend Guest

    [blu|shark] wrote:

    > i seem to fail to understand how _depth of field preview_ button on Canon
    > EOS 300D works. manual lacks a thorough explanation, and when i use the
    > button (in one of the creative modes), i don't notice any difference.
    > i use 3.5AV thinking it should maximize the effect, but nothing really
    > happens. (at least nothing i notice)
    >
    > i'd appreciate a few words of explanation on this subject, and also a tip
    > on whether i should hold the button or just press it when i use it :)


    When you look through your viewfinder, you're looking through your lens.
    (That's what SLR's are all about :)

    EOS lenses have an iris made up of metal blades.. These blades work like
    your eye and control the amount of light entering the lens by varying the
    size of the opening. As you increase the f number, opening gets
    smaller. If you reduce the f number the opening gets bigger.

    DOF depends on the size of the iris opening.. A very large opening creates
    a shallow depth of field.. (subject in focus, background out of focus).
    A tiny opening provides a large depth of field. (subject and background
    both in focus).

    Here's the trick.. In EOS lenses, the iris doesn't shrink the opening *until
    the shutter release is pressed*. It happens just before the mirror flips and
    the shutter curtains move.

    Because of this, you are always looking through the lens with the iris
    wide open. If your lens is an f/3.5 lens, then you're seeing the scene
    at f/3.5 no matter what you've set your f stop to. Because of that,
    you can't see what in the image (besides your subject) will be in focus
    or out of focus.

    By pushing the DOF preview button, you cause the iris to do what it's
    going to do when you press the shutter release. If you set the camera
    to f/22 the iris will shrink the opening to a tiny circle. Now you
    can see exactly what will be in focus or out of focus.. The only
    drawback is that things get pretty dark because the opening is smaller.

    Try this.. Put your camera in Av mode. Set the aperture to f/22
    Now turn the camera towards you and look down the lens.. Press the
    DOF preveiw button.. You'll see the iris open and close from wide
    open to f/22 as you press the DOF button.. Look through the viewfinder..
    Note objects in the far off distance as you press the button.
     
    Jim Townsend, Jan 15, 2004
    #5
  6. "[blu|shark]" <> wrote in message news:<1017l0mjcbzff$.1q78q5ls7d9lo$>...
    > i seem to fail to understand how _depth of field preview_ button on Canon
    > EOS 300D works. manual lacks a thorough explanation, and when i use the
    > button (in one of the creative modes), i don't notice any difference.
    > i use 3.5AV thinking it should maximize the effect, but nothing really
    > happens. (at least nothing i notice)
    >
    > i'd appreciate a few words of explanation on this subject, and also a tip
    > on whether i should hold the button or just press it when i use it :)
    >


    When you press the button, the diaphragm of your lens will close to
    its set number. If you set it to a high number, the image will be
    darker, but the depth of field will be bigger. If you set it to a
    small number, you may not notice the change.

    To see the effect, use the Av mode, and try different diaphragm
    settings.
     
    jerry_tig2003, Jan 15, 2004
    #6
  7. [blu|shark]

    Tony Spadaro Guest

    Try it at f16. There is an article here, on using the DOF preview button:
    http://www.chapelhillnoir.com/mani/techs/mdofwalk.html
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    "jerry_tig2003" <> wrote in message
    news:...
    > "[blu|shark]" <> wrote in message

    news:<1017l0mjcbzff$.1q78q5ls7d9lo$>...
    > > i seem to fail to understand how _depth of field preview_ button on

    Canon
    > > EOS 300D works. manual lacks a thorough explanation, and when i use the
    > > button (in one of the creative modes), i don't notice any difference.
    > > i use 3.5AV thinking it should maximize the effect, but nothing really
    > > happens. (at least nothing i notice)
    > >
    > > i'd appreciate a few words of explanation on this subject, and also a

    tip
    > > on whether i should hold the button or just press it when i use it :)
    > >

    >
    > When you press the button, the diaphragm of your lens will close to
    > its set number. If you set it to a high number, the image will be
    > darker, but the depth of field will be bigger. If you set it to a
    > small number, you may not notice the change.
    >
    > To see the effect, use the Av mode, and try different diaphragm
    > settings.
     
    Tony Spadaro, Jan 15, 2004
    #7
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