Exposure compensation

Discussion in 'Photography Beginners' Forum' started by burstintoflame81, Oct 22, 2009.

  1. burstintoflame81

    burstintoflame81 TPF Noob!

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    I am trying to learn more about the camera and its functions. I just wanted to get some clarity on the Exposure compensation. My current understanding is that, if a picture is too bright or too dark ( but I want to retain my current DOF and shutter speed ) then I can tweak the exposure which is basically making the sensor more or less sensetive? Is this correct?

    For instance, I was shooting a white swan the other day and I was getting a lot of blown out area in the white feathers but wanted my depth of field and shutter speed to remain the same. Would a 1/3 or 1/2 stop down on the exposure comp been a wise choice to remedy the problem?
     
  2. hulk

    hulk TPF Noob!

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    From what I understand, EC is to be used when you use your camera's metering system (ie. anything other than Manual mode). If it so happens that your camera meters the scene incorrectly, you can use the EC to alternate the exposure value. For example, if you're shooting a white dog in the snow, the camera will most likely underexpose the picture, so you'll have to compensate for it by using EC.

    Edit: To add to this, when you use the EC, the camera will modify either the aperture or the shutter speed (or both) depending on if you're in A, S, or P more.
     
  3. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Correct you can - using the ISO however. The three components that make up an exposure in a camera are the aperture, shutter speed and ISO - the modes on the camera only ever adjust how you reach those 3 settings for the shot.
    A lower ISO will make your sensor less sensative to light and also mean that you have far less noise in your shot (those little dotty things in the background mostly) whilst a higher ISO means more senstive and more noise (which at higher levels leads to a loss of sharpness and detail in the shot).

    When you use exposure compensation the camera takes its meter reading as normal, but then instead of trying to adjust the settings it has under its control (which is different depending what mode your shooting in) to get a "proper" exposure it tried to either under or over expose the shot depending on what compensation you selected.


    It would depend what mode you were shooting in - but essentially if your ISO was as low as it could go (ISO 100 on most cameras) then you would have to adjust either your shutter speed (faster) or your aperture (smaller aperture, bigger f number and thus more depth of field). In the secen you describe the aperture you want to stay the same, but the shutter speed you can have risen and it will just freeze the action that little bit more.

    Of course if you want to just adjust one setting like that you have 2 options - full manual mode or aperture priority mode - where you dial in the aperture (to keep it fixed) and you dial in the ISO (low as you can go is the general rule) and then the camera picks the shutter speed. Now in bright light and against a white subject the camera meter can give you a reading which will overexpose that area - essentailly the meter has been tricked into that and now you have to compensate by dialing in the underexposure - and thus telling the camera to shoot with a faster shutter speed.

    For more help I strongly recomend the book Understanding Exposure by Bryan Peterson - it will give you more depth to this whilst still being aimed at the beginner photographer
     
  4. burstintoflame81

    burstintoflame81 TPF Noob!

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    Yes, I usually us Av mode or manual. I just wasn't sure if changing the compensation was in fact changing the shutter speed or just altering how the system decides on which one it chooses or whatever. I guess the simplest thing would be to speed up the shutter speed just slightly and hopefully that would still give me whatever type of movement ( blurred or frozen ) that I was trying to achieve. Thanks for the help.
     
  5. tom123

    tom123 TPF Noob!

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    Exposure compensation either makes your photo lighter or darker depending on which way you compensate. Which parameter is going to change depends on your shooting mode. If you use aperture priority, then the shutter speed is going to change. If you use the exposure (shutter speed) priority, the aperture is going to change. Exposure compensation does not exist in manual mode because then you control both the aperture and shutter speed. Generally exposure compensation does not have anything to do with the sensor sensitivity.
     

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