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Exposure question

Discussion in 'Nikon DX DSLR Forum' started by D. L. Miller, Jun 14, 2005.

  1. Under identical lighting the following happens.
    Camera D2x
    Lens 17-55mm f/2.8
    Set camera to "A" priority:
    Locked down on a tripod

    I set the f stop to f/2.8 and the camera sets the speed at 1/500 of a sec and it is a perfect combo and the pictures comes out perfect

    I didn't move the camera and maybe 1 minute between takes.

    Now I set the f stop to 5.6 and the camera sets the speed to 1/250.
    and for discussion lets say theses settings are also a perfect combo, but it is actually .7 EV off. The shot is too dark. If I bracket by .7 EV the picture comes out perfect on the + .7EV bracket.

    Can I assume anything? At first I thought it has to be a camera malfunction. Those the camera says f/5.6 and 1/250 of a sec, it isn't happening. (?)

    But the same steps taken with my 50mm f/1.8 hits both shots right on.

    Am I crazy and don't know anything about light and lens (which I'll admit) or do I need to find help at Nikon.
  2. marc

    marc Guest

    1. are you inside or outside
    2. bracket, how many steps
    3. iso?
    4. it is possible you are underexposing
    5. what are you shooting
    6. put the camera on p mode and see what it does
    7. if indoor, what wb setting

    there are many questions, you need to give more info

    are you using flash?

  3. Marc,
    1. Outside with good light, sunny day
    2. 3 each side at .3 EV
    3. ISO: 200
    4. Using camera meter with "A" priority
    5. Brown Firehouse
    6. Haven't done that yet, was trying to control "A" setting
    7. N/A : outside.

    The meter says the exposure is correct, but it will get darker as I stop it down even though the speed does adjust so the picture should have correct exposure.

    My spot meter function if off 1 f stop. Picture too dark. I adjusted that in the menu settings.
  4. Danny Lee

    Danny Lee Guest

    Are you shooting the same exact scene? If 1/500 f2.8 is correct then 1/250 4.0 should be correct also.
  5. thomas

    thomas Guest

    .7 ev off

    Hi Dan

    Mine do the same. At F:8 it is even worse = 1.0 ev too dark. It is not the camera, but the lens. Ron Resnick also noted this when he tested the lens.
  6. Chris101


    Feb 2, 2005
    Ummm, maybe I'm looking at it wrong, but you gave it twice the exposure time (1/500 -> 1/250 second) but then closed the aperture to four times (2 stops) less light (f/2.8 -> f/5.6).

    If you give it twice the time (one stop more light) then shouldn't you also close the aperture by one stop (to f/4, one stop less?)

    (PS, mathmatically, the f/stop is a function of the square of the light admitted (2X the diameter is 2 squared (4) times the area admitting light.) So double the f-number is four times as much light.)
  7. Chris 101,

    You are correct. I met to say if the f stop is correct for the speed at a given combo, why is it off for a different f stop with the correct speed.

    seeing thomas's reponse might be the answer.

    I'll check out Ron's review. I hope I am missing something. If not, then I can't trust the camer'a light meter at certain f stop and speed settings.
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