Exposure compensation

Discussion in 'Digital Photography' started by LouisB, Nov 15, 2006.

  1. LouisB

    LouisB Guest

    OK, I'm a little confused. It has been years since I did any serious
    photography and I'm staggered at what I have forgotten.

    These new digital cameras have lots of easy ways to dial in +ve or -ve EV in
    increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I can
    even bracket in any of those ranges.

    I'm just a little unsure as to the rules here. How exactly is the exposure
    altered by using positive or negative compensation? What are the basic rules
    for deciding when and how to compensate?

    I shoot mainly in RAW mode so I can play around with the compensation when I
    post process but I'd like to know whether that absolves me from even
    worrying about exposure compensation, at all?

    If anyone has the patience to succinctly explain this or point me in the
    right direction, I would be eternally grateful.

    LouisB
    ------
    "I'm a half-wit. I sold the other half on e-Bay"
    LouisB, Nov 15, 2006
    #1
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  2. LouisB

    rowan194 Guest

    LouisB wrote:
    > OK, I'm a little confused. It has been years since I did any serious
    > photography and I'm staggered at what I have forgotten.
    >
    > These new digital cameras have lots of easy ways to dial in +ve or -ve EV in
    > increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I can
    > even bracket in any of those ranges.
    >
    > I'm just a little unsure as to the rules here. How exactly is the exposure
    > altered by using positive or negative compensation? What are the basic rules
    > for deciding when and how to compensate?
    >
    > I shoot mainly in RAW mode so I can play around with the compensation when I
    > post process but I'd like to know whether that absolves me from even
    > worrying about exposure compensation, at all?
    >
    > If anyone has the patience to succinctly explain this or point me in the
    > right direction, I would be eternally grateful.


    Exposure compensation allows you to "shift" the camera's automatically
    chosen shutter/aperture values in order to expose more or less.
    Exposure meters are not perfect so there are some tricky (and even not
    so tricky) situations where you'll need to help them in order to get
    the best possible exposure. Basically anything which fools the
    averaging effect of the exposure meter will probably need some manual
    adjustment.

    I usually use exposure compensation in conjunction with the histogram
    which is shown after the shot is taken - the exposure meter makes an
    educated guess before the shot, the histogram shows exactly how that
    estimated exposure has been captured. For myself, if there seems to be
    more than about a stop that is unused I'll retake the shot with
    positive exposure compensation. If the histogram (or image) shows blown
    highlights then I'll retake it with negative exposure compensation.

    By the way, RAW is not magic: if you increase the exposure too much in
    post processing you'll bring out noticeable noise. If you have
    overexposed the shot then negative exposure compensation may require
    some "guessing" by the RAW converter as one or more of the R, G and B
    channels are overexposed (clipped) beyond their maximum values.

    If you do a Google search for "exposure compensation" you should be
    able to find out more.
    rowan194, Nov 15, 2006
    #2
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  3. LouisB

    jeremy Guest

    jeremy, Nov 15, 2006
    #3
  4. "LouisB" <> wrote in message
    news:qxJ6h.134560$...
    > OK, I'm a little confused. It has been years since I did any serious
    > photography and I'm staggered at what I have forgotten.
    >
    > These new digital cameras have lots of easy ways to dial in +ve or -ve EV
    > in increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I
    > can even bracket in any of those ranges.
    >
    > I'm just a little unsure as to the rules here. How exactly is the exposure
    > altered by using positive or negative compensation? What are the basic
    > rules for deciding when and how to compensate?


    The camera is metering for neutral gray. When you are in the snow, the
    camera will turn the snow to gray. So, you dial in +EV. When you are in
    the dark, the camera will change black to neutral gray. So, you dial
    in -EV.

    When in doubt, you could use EV bracketing (the camera will take three shots
    .... depends on your camera).

    If you are serious, use a spot meter and the zone system!
    Charles Schuler, Nov 15, 2006
    #4
  5. LouisB

    Paul Mitchum Guest

    LouisB <> wrote:

    > OK, I'm a little confused. It has been years since I did any serious
    > photography and I'm staggered at what I have forgotten.
    >
    > These new digital cameras have lots of easy ways to dial in +ve or -ve EV
    > in increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I
    > can even bracket in any of those ranges.
    >
    > I'm just a little unsure as to the rules here. How exactly is the exposure
    > altered by using positive or negative compensation? What are the basic
    > rules for deciding when and how to compensate?
    >
    > I shoot mainly in RAW mode so I can play around with the compensation when
    > I post process but I'd like to know whether that absolves me from even
    > worrying about exposure compensation, at all?
    >
    > If anyone has the patience to succinctly explain this or point me in the
    > right direction, I would be eternally grateful.


    The classic example is a back-lit scene. Say you want to photograph a
    person standing in front of a bright sky, without using fill flash. The
    camera's light meter will likely meter for the bright sky, rather than
    the shadowy figure, leaving you with an image of an indistinct
    sillhouette. So you dial in +1.5 EV (or so). The camera still meters off
    the sky as before, but boosts the exposure time and/or aperture
    (depending on how the camera figures these things out), and you end up
    with a washed-out sky and a well-exposed person.

    If your camera allows it, you can do the same thing by just changing the
    aperture and/or shutter speed yourself. EV is measured in stops, so
    opening the aperture one stop gives you +1 EV. Doubling the time of the
    shutter speed is +1 EV. Do both and get +2 EV.

    As to when to use EV compensation: That depends on what you're
    photographing. In the above example, if you *wanted* a sillhouette
    against the sky, then boosting the EV would be a bad idea. It's a
    judgement call.

    HTH.
    Paul Mitchum, Nov 15, 2006
    #5
  6. LouisB wrote:
    > OK, I'm a little confused. It has been years since I did any serious
    > photography and I'm staggered at what I have forgotten.
    >
    > These new digital cameras have lots of easy ways to dial in +ve or -ve EV in
    > increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I can
    > even bracket in any of those ranges.
    >
    > I'm just a little unsure as to the rules here. How exactly is the exposure
    > altered by using positive or negative compensation? What are the basic rules
    > for deciding when and how to compensate?
    >
    > I shoot mainly in RAW mode so I can play around with the compensation when I
    > post process but I'd like to know whether that absolves me from even
    > worrying about exposure compensation, at all?


    No. It's way better to nail the exposure as close as you can, whether or
    not you shoot RAW, even though it is more forgiving on luminance and
    color balance.

    --
    John McWilliams
    John McWilliams, Nov 16, 2006
    #6
  7. "LouisB" <> wrote:
    >OK, I'm a little confused. It has been years since I did any serious
    >photography and I'm staggered at what I have forgotten.
    >
    >These new digital cameras have lots of easy ways to dial in +ve or -ve EV in
    >increments (mine is 0.3, 0.5 or 1 depending on how you customise it). I can
    >even bracket in any of those ranges.
    >
    >I'm just a little unsure as to the rules here. How exactly is the exposure
    >altered by using positive or negative compensation? What are the basic rules
    >for deciding when and how to compensate?


    The camera's light meter is calibrated to assume a scene
    averages at about 14-18% gray. If the scene does average that,
    your exposure will probably be about right; if a scene doesn't,
    then you can use exposure compensation to re-calibrate the light
    meter.

    But if you shoot a scene that is mostly white (on a winter day
    outside in the snow, for example), the scene's average will not
    be middle gray. If you do not adjust the meter, it will meter
    it for exposure as middle gray, and the resulting images will
    have gray snow and be very drab.

    Instead, what you do is dial in +1.5 EV, which tells the light
    meter than the average is going to be about 1.5 fstops brighter
    than middle gray.

    Likewise if you take a picture where the background is very dark
    it may be necessary to dial in a negative EV number.

    All it does is calibrate the exposure meter. The specific
    effects from that depend on the various exposure modes available
    on your camera. For example, if you use "manual mode" the
    immediate affect is only to tell you that you are over/under
    exposing by the number of fstops you have dialed in as EV
    compensation. If you don't adjust the exposure, nothing
    changes... You could just as well leave the camera set to 0 EV
    and simply set the aperture/shutter to over/under expose.

    But with any kind of "automatic" exposure mode, something will
    change, so setting meter calibration with EV compensation is
    nice.


    >I shoot mainly in RAW mode so I can play around with the compensation when I
    >post process but I'd like to know whether that absolves me from even
    >worrying about exposure compensation, at all?


    Setting exposure compensation is the right way to adjust
    exposure when you use any "automatic" exposure mode in the
    camera. It is perhaps a waste of time (but may be easy just
    because it is commonly used) when shooting in "manual" exposure
    mode.

    The trick with digital and RAW mode though, is to *ignore* the
    meter anyway! (Okay, not totally... but don't use it for
    anything other than an quick way to get an initial starting
    point for exposure.) Set your camera to either show a
    histogram or better yet a "blinking over exposure" LCD display.
    Use the exposure meter to determine initial settings, but look
    at the histogram/blinking-display to determine if exposure is
    right. Between the two, what you want is highlights that should
    not be blown to be almost up against the right side of the
    histogram. If there are some highlights (light sources, for
    example) that you are going to allow to be blown out, a blinking
    display is the only way to know what is over exposed and what is
    not.

    Just increase exposure until the desired highlights blink,
    and then back off until they stop. It is fairly easy to get
    within 1/3 fstop.

    The essential effect of setting exposure as above is that the
    image will record the maximum dynamic range possible. It might
    well be that the "highlights" are NOT white! But if the
    highlights are actually gray, you will record data well down
    into the shadows that would be lost if those gray highlights are
    set to expose in mid range. With post processing you can adjust
    to restore the highlights at middle grey... *and* if you want
    it is also possible to "pull" the shadows up too, without the
    noise and posterization that would result if the gray had been
    exposed as gray! (All of which is part of what makes digital so
    much fun. That can be done with film too, but it is not so
    easy.)

    --
    Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
    Ukpeagvik (Barrow, Alaska)
    Floyd L. Davidson, Nov 16, 2006
    #7
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