Pretty good article on medium format cameras

Discussion in 'Digital SLR' started by RichA, Aug 23, 2008.

  1. RichA

    RichA Guest

    RichA, Aug 23, 2008
    1. Advertisements

  2. RichA

    Guest Guest

    larger *sensor*.
    Guest, Aug 23, 2008
    1. Advertisements

  3. RichA

    Guest Guest

    there's no ambiguity about what 'sensor' means.
    where did you get the idea that 'sensor' means the front of the lens?
    Guest, Aug 24, 2008
  4. Not true.
    Take a large format lens and camera.
    Enter a completely constant lit room.
    Where the film should be, mount a 4x6mm 10 MPix sensor.
    Choose a exposure time, ISO setting and f-stop.
    Expose your sensor and read it out.

    Now replace the tiny 4x6mm sensor with a 60x90mm 10 MPix
    sensor, and expose it at the same exposure time, ISO setting
    and f-stop.

    Tell me, will the larger sensor have collected more photons?
    Will each pixel of the larger sensor have collected more photons?

    PS: Now remember that f-stops are independent of image circles.

    Wolfgang Weisselberg, Aug 27, 2008
  5. RichA

    Me Guest

    At the appropriate f-stops required to produce an image at a standard
    size with the same DOF, or doesn't composition matter in theoretical
    Me, Aug 28, 2008
  6. Oh, you are right, how stupid of me!

    I was just proving that "You will only get more photons if you
    use a physically larger lens" is wrong. Every time someone
    moves a full frame lens from a crop to a full frame body
    exactly that happens. (Yes, FF bodies are better at light
    gathering, all things being equal, see below.)

    But, as requested, let's do practical photography:

    a) Portrait, "normal" (50mm in 35mm equivalent) lens, 1 meter
    distance between camera and object, DOF ~10cm. Target is a
    20x30cm photo viewed at 41cm (the diagonal length)
    b) Landscape, "wide" (28mm in 35mm equivalent) lens, put everything
    from 2.5m onward in DOF. Target is a 2x1.5 meter print for
    the wall, viewed at ~1.56 meters distance (where the field
    of view is the same as the real landscape)

    Sensor used: 4x6mm 60x90mm
    Area: 24mm² 5400mm²
    a) Pixels needed * 2865x1910 i.e. 5.5 MPix *
    f-stop 1.0 16
    resulting DOF[1] 11.69cm 11.12cm

    b) Pixels needed * 4408x2938 i.e. 13MPix *
    f-stop 2.0 32
    resulting DOF[1] 2.17m 2.29m

    24mm² / 1.0 => 24
    5400mm² / 16 => 337.5

    24mm² / 2 => 12
    5400mm² / 32 => 168.75

    337.5 : 24 = 14:1
    168.75 : 12 = 14:1

    As you can see, the 60x90mm sensor enjoys a 14-fold light gathering
    advantage --- that's more than 4 stops --- over the 4x6mm sensor.
    Actually, 14:1 is the difference between 60 and 4mm, between 90
    and 6mm.

    Once again it's proven that quadrupling the sensor size needs
    doubling the f-stop (for the same DOF) and still doubles the
    light gathering capability.

    And practical photography also has a few problems with the
    necessary f/1.0 lenses for these tiny chips.


    [1] Includes diffraction effects.
    Wolfgang Weisselberg, Aug 29, 2008
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.