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Thread: What does it mean to "meter off of ..."

  1. #1

    Join Date
    Mar 2011
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    Lachine, Quebec, Canada
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    Real Name
    Erik

    What does it mean to "meter off of ..."

    Hello,

    I have seen in discussion where someone is told to meter off of, say the black door.
    How do you do that? Does the camera meter the scene from the center of the lens? I'm sure there is a difference in spot meter VS matrix metering when pointing the camera in a particular scene.

    If we stay with the black door. If the black door is to the left of the yellow wall in the scene, I'm guessing spot metering will read from the yellow wall. Matrix will read from the entire scene.

    Now, what if I wanted to meter off of the door but keep my composition? Do I point the camera to the door while on spot metering, exposure lock, then re-compose?

    Thanks,

    Erik

    Thanks,

    Erik

  2. #2

    Join Date
    Aug 2010
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    Stockholm, Sweden (and sometimes Santiago de Cuba)
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    Real Name
    Urban Domeij

    Re: What does it mean to "meter off of ..."

    It is not quite as simple as metering the door and lock. You must also decide where to put the tone of the door in the range of the picture; i.e. if the door is black, it is supposed to appear black in the image. When spot metering, the Zone System should be applied, and it helps to first have learned it. However, you need not understand all of its intricacies in order to apply it.

    When spot metering with the camera, mostly it is the centre spot that limits where you read. So you aim it at the door, and it gives you a medium gray value for the door. You decide to put the door two (2, 2 or 3) stops darker, because you don't want it to be medium grey and all light tones blown out.

    How much to compensate for the tone is a matter of knowing your camera/sensor and your way of converting.

    After the shot when you chimp with highlight warning, you can see whether everything fell within the possible dynamic range of the sensor at actual ISO setting. When DR is high, you might need to use base ISO to accomodate a wider range of tones.

    So in essence: You decide to put the black door three stops below, adjust compensation to -3 and spot meter the door, lock exposure, recompose and shoot. More commonly, you spot meter off the brightest highlight with appropriate plus compensation in the image you wish to take, lock exposure, recompose and shoot.

  3. #3

    Join Date
    Dec 2008
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    New Zealand
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    Have a guess :)

    Re: What does it mean to "meter off of ..."

    Hi Erik,

    Cameras have different metering modes - usually:

    - Evaluative / Matrix (Canon / Nikon)

    - Partial

    - Centre Weighted Average

    - Spot

    In essence all you're doing by using any one of them is telling the camera how much (and which) part of your composition to consider when deciding what combination of aperture / shutterspeed / ISO to select for you.

    Case in point; put someone in front of a window (inside) - put your camera on evaluative / matrix - and take a shot that includes the window. Assuming that it's a bright sunny day, the camera will give you an exposure that tries to protect some of what's visible through the window, and the person will be little more than a silhouette. In contrast (little photographer humour there!), if you put the camera into spot-metering mode - point it at the face of your associate - and you'll get an entirely different exposure (the face will look pretty good, but they'll be surrounded by a sea of white as the backlighting over-powers the sensor).

    So in the first case, evaluative / matrix metering told the camera that EVERYTHING was important, but in the second case, spot-metering told the camera that only the face of your associate was important. Partial metering is 1/2 way inbetween these two, and centre-weighted average says in essence that "everything is important, but what's in the centre of the composition is even MORE important - so err on the side that gets what's in the centre close to being right if possible.

    What a lot of people DON'T understand though is that the camera essentially assumes that what you're pointing at is a medium grey (in terms of brightness, not colour) - if you photograph a black cat on a black rug the camera will expose it as a grey cat on a grey rug; shoot a white bear in the snow and the camera will give you a grey bear in grey snow (keep in mind that the camera doesn't know what you're shooting). When you use wide-scope metering modes like evaluative / matrix you normally get a good exposure because most scenes average out to 18% gray (which is why this figure is used in the first place), and although you may need some exposure compensation, generally it's minimal for normal scenes. Different story for spot metering though, because what you're metering probably ISN'T representative of the entire scene - so if what you're metering ISN'T a medium grey, it WILL be when you look at the shot afterwards, unless you add or subtract exposure compensation.

    So for spot metering - if you're spot metering your black door - and because black is 2 stops below medium grey - you'll want to tell the camera to go 2 stops lower than it would have; conversely, if you're spot metering something white (say brides dress), the camera will assume that it's a grey dress unless you add 2 stops of exposure compensation to make it white again.

    Normally cameras will spot-meter off the centre AF point, but be aware that some cameras (like my Canon 1Ds3) have an option that tells the camera to spot-meter off the currently selected AF point (which may well not be the centre one) - so just something to be aware of.

    Now, what if I wanted to meter off of the door but keep my composition? Do I point the camera to the door while on spot metering, exposure lock, then re-compose?
    There's a few ways to do it, but in essence, yes.

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