Evaluative mode locks exposure at autofocus

Discussion in 'Canon EOS' started by mendel_leisk, Oct 27, 2006.

  1. Like to confirm this is proper behavior for the 5D:

    1. If I have the camera in Evaluative metering mode, in either P, Tv or Av, and
    with autofocus on: exposure is locked at time of autofocus. If I pan about
    after acquiring focus, with the button half-depressed, aperture and shutter
    speed do not change, regardless of change in light levels. If I release the
    half-depressed shutter, the displayed aperture and shutter speed start changing
    again, as I pan through differently lit areas.

    2. If I repeat the exercise with the camera in any of the other metering modes,
    Partial, Spot or Center Weighted, autofocus and then pan with shutter-button
    half-depressed, aperture and shutter speed *do* change, as I pan to lighter or
    darker subjects.

    3. If I have the camera in Evaluative metering mode, but with autofocus off,
    then the metering behaves per number 2.

    In short, with Evaluative metering mode, acquiring autofocus also locks
    exposure, as long as the shutter is half-depressed. No other meter mode does
    this.

    FYI, I have custom function 4 set to 0.

    Sorry if this has been covered before, I looked but didn't find anything. My
    search string was pretty verbose ;)
     
  2. That behavior is correct. Basically the Evaluative metering depends on the focus point used. When you focus, the camera evaluates and determines the metering dependent upon that point. If you lock focus and recompose, it will "hold" that meter reading....even if the original subject is moved out of the frame -jeffl
     
  3. oh... and if the lens is in manual mode, the camera and lens don't communicate fully...the camera doesn't have a subject on which it is focused and has evaluated the exposure. If you focus manually while leaving the lens in autofocus, the exposure will hold as in your situation #1.
     
  4. Yep it's normal. All EOS bodies work the same.
     
  5. The description of the function of AE lock is extremely poor (and misleading) in the manual. The manual says "If the AF mode is One-Shot AF or AI Focus AF and the metering mode is Evaluative, pressing the shutter button halfway will automatically set AE lock at the same time when focus is achieved.

    Later in the manual, there's a small matrix describing AE lock behavior dependent upon metering mode and AF point selection. For Evaluative Metering, it says: "Automatic AF point selection: AE lock is applied at the AF point that achieved focus". "Manual AF point selection: AE Lock is applied at the selected AF point" Then a footnote: * When the lens' focus switch is set to <MF>, AE Lock is applied at the center AF point.



    I read that as meaning that when the camera achieves focus (which it'll still do in MF mode), it would lock the exposure at that time. However, even while the focus lock annunciator is lit, the lens is in MF mode, the camera is in Evaluative metering, and CF4-0 is set, the exposure WILL still change.

    Even reading this strictly, I would argue that the camera IS in One-shot AF mode; only the lens is not. This fine point is not discussed in the manual anywhere I can find.

    Either there's something in the manual I have not yet found, or the manual is mis-written or ambiguous.

    There are several deficiencies like this in the EOS manuals, and they're extremely irritating due to the complex nature of the interactions of many different camera settings.
     
  6. Thanks all. As you said, Jeff, I was wondering about the implications for lock focus and recompose. If I don't like this behavior, I guess my options are:

    1. Pick another meter mode, say Center Weighted, where exposure *is* constantly updating as you pan.

    2. Set Custom Function 4 to 1, and practice with it. I like the concept, but seem to have 2 left feet with this setup ;D
     
  7. Thanks Brian.
     

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