Life-size objects in the viewfinder

Discussion in 'Digital Photography' started by sfeher@gmail.com, Jul 16, 2006.

  1. Guest

    Hi All,

    As I am trying to educate myself in the physics of the camera, I have a
    question regarding the focal length for which you get objects to
    *appear* life-size in the viewfinder? Is this important in any way?

    Looking through the viewfinder the objects appear to be life-size at
    aprox. 70mm ?! This happens for both DSLR (D70 - 18-70 lens) and 35mm
    SLR (Elan7 28-90
    lens - which has a bigger viewfinder).

    I thought the focal length for real life-size would be 43mm for 35mm
    camera and somewhat proportional(1.5x) for the DSLR, hence my confusion
    when I actually got 70mm for each one of them.

    I hope my question is somewhat clear. It could be that I am looking at
    the problem from a weird perspective as I am learning these things. If
    so please let me know.

    Regards,
    Sebastian
    , Jul 16, 2006
    #1
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  2. k-man Guest

    You might be confusing focal length and magnification. Magnification
    is where you get "lifesize" images. This is particularly important
    with macros, where often you would want a magnification of 1:1. This
    is not a very detailed explanation, I know. But there are a lot of
    sites out there that have all the details.

    Kevin



    wrote:
    > Hi All,
    >
    > As I am trying to educate myself in the physics of the camera, I have a
    > question regarding the focal length for which you get objects to
    > *appear* life-size in the viewfinder? Is this important in any way?
    >
    > Looking through the viewfinder the objects appear to be life-size at
    > aprox. 70mm ?! This happens for both DSLR (D70 - 18-70 lens) and 35mm
    > SLR (Elan7 28-90
    > lens - which has a bigger viewfinder).
    >
    > I thought the focal length for real life-size would be 43mm for 35mm
    > camera and somewhat proportional(1.5x) for the DSLR, hence my confusion
    > when I actually got 70mm for each one of them.
    >
    > I hope my question is somewhat clear. It could be that I am looking at
    > the problem from a weird perspective as I am learning these things. If
    > so please let me know.
    >
    > Regards,
    > Sebastian
    k-man, Jul 17, 2006
    #2
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  3. Guest

    wrote:
    > Hi All,
    >
    > As I am trying to educate myself in the physics of the camera, I have a
    > question regarding the focal length for which you get objects to
    > *appear* life-size in the viewfinder? Is this important in any way?
    >
    > Looking through the viewfinder the objects appear to be life-size at
    > aprox. 70mm ?! This happens for both DSLR (D70 - 18-70 lens) and 35mm
    > SLR (Elan7 28-90
    > lens - which has a bigger viewfinder).
    >
    > I thought the focal length for real life-size would be 43mm for 35mm
    > camera and somewhat proportional(1.5x) for the DSLR, hence my confusion
    > when I actually got 70mm for each one of them.
    >
    > I hope my question is somewhat clear. It could be that I am looking at
    > the problem from a weird perspective as I am learning these things. If
    > so please let me know.
    >


    This will vary with the camera. Most DSLR viewfinders are essentially
    a telescope. The prism re-inverts the image, so the type of telescope
    is the same as a 'spotting scope'.

    A telescope does have magnification, though not the same mathematically
    as the 'magnification' of a simple lens. The telescope 'magnification'
    is in angle space. The magnification of the scope depends on the ratio
    of the fl of the eyepiece lens to the objective lens. Thus if two
    cameras have different eyepiece lens fl, the magnifications will be
    different even with the same fl objective lens.
    > Regards,
    > Sebastian
    , Jul 17, 2006
    #3
  4. On 16 Jul 2006 11:13:31 -0700, in rec.photo.digital wrote:

    >I thought the focal length for real life-size would be 43mm for 35mm
    >camera and somewhat proportional(1.5x) for the DSLR, hence my confusion
    >when I actually got 70mm for each one of them.


    You are forgetting to also take into account the magnification of the
    viewfinder. For the D70, copied from the fine manual:

    Magnification Approximately 0.75× (50-mm lens at infi nity; –1.0 m–1)
    --
    Ed Ruf ()
    http://edwardgruf.com/Digital_Photography/General/index.html
    Ed Ruf (REPLY to E-MAIL IN SIG!), Jul 17, 2006
    #4
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