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Thread: how does a camera do exposure compensation?

  1. #1

    Default how does a camera do exposure compensation?

    really, how does a camera do it?

    does it change the shutter speed? or the aperture? does it depend on the camera mode eg A, M, P or S (or Tv)?

    assume if the camera changes its shutter speed to effect the compensation and the camera is already set to the highest speed, does it mean putting -1 compensation have no effect?

    can somebody pls enlighten me? try to find answer in many book, but there is no satisfying answer.

    thank q.

  2. #2
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    IF you are in Av, camera does it by altering shutter speed.

    If you are in Tv, camera does it by altering aperture.

    If you are in P/Auto/preset/scene modes, the camera follows it's own algorithm.

    If you are in M, and you don't follow meter, exposure compensation has no effect.

    Regards
    CK

  3. #3
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    Quote Originally Posted by firstmoon
    assume if the camera changes its shutter speed to effect the compensation and the camera is already set to the highest speed, does it mean putting -1 compensation have no effect?
    Oh, left this out. Yes, if it has reached the limit (highest possible shutter, the compensation will have no effect).

    Regards
    CK

  4. #4
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    Quote Originally Posted by firstmoon
    really, how does a camera do it?

    does it change the shutter speed? or the aperture? does it depend on the camera mode eg A, M, P or S (or Tv)?

    assume if the camera changes its shutter speed to effect the compensation and the camera is already set to the highest speed, does it mean putting -1 compensation have no effect?

    can somebody pls enlighten me? try to find answer in many book, but there is no satisfying answer.

    thank q.
    A proper exposure is determined by both shutter speed and aperature size. In manual mode, you control both shutter speed and aperature size.

    In Av mode, you control the aperature but the camera computer will calulate a n appropriate shutter speed for a proper exposure.

    Similarly, in Tv mode, you control the shutter speed and the camara calculates the appropriate aperature size.

    In P mode. Basically the camera sets the aperature to the largest and then computes the equivalent shutter speed.

  5. #5

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    I wonder that with digital,,, does the ISO setting change if limits have been reached?
    Gallery | Facebook Page Spreading the Good photography.

  6. #6

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    Quote Originally Posted by firstmoon
    really, how does a camera do it?

    does it change the shutter speed? or the aperture? does it depend on the camera mode eg A, M, P or S (or Tv)?
    View it as this way:
    P: Full Auto
    S: Half Manual
    A: Half Manual
    M: Full Manual

    In S mode, it shutter prioity. You adjust the shutter speed and the camera adjust the aperture to gives you the correct exposure*
    In A mode, it aperture priority. You adjust the aperture and the camera adjust the shutter till you get a correct exposure*
    In M mode, it full manual, you adjust both the shutter and aperture.
    Sorri, i dunno abt P mode though.

    *correct exposure: this so call correct exposure is wat is deem correct by the camera metering. however wat is deem correct by the camera might not always be correct. This is one of the reason why you use a EV compensation. i,e when metering against a scene of snow, your camera might actually gives you a higher reading then it should be, thus giving you a greyish instead of a pure white snow when you follow the 'correct exposure' thus we actually use a compensation of +1- +2 to compensate for the flaws of the meter.


    Quote Originally Posted by firstmoon
    assume if the camera changes its shutter speed to effect the compensation and the camera is already set to the highest speed, does it mean putting -1 compensation have no effect?

    can somebody pls enlighten me? try to find answer in many book, but there is no satisfying answer.

    thank q.
    by setting a compenation of -1 would actually require you to use a higher shutter speed which your camera already cannot support.
    if your qns is the oppz, in the case of putting your compensation to + , true, it will let you take w a slower shutter speed, and if this falls within your camera supported shutter speed, you can take the shot. but wat will happen?
    unless you know wat you are doing, by using using a + compensation you are actually overexposing your shot, and rendering the subject you meter to become overexpose. In general this should not be the way to do when your camera hit the highest shutter speed.

    in general, i would personal feel tat seldom would you hit the highest shutter speed, unless you using a very high speed film in daylight, or shooting with 1.4, or shooting at the sun.
    if you do have the prob of hitting the highest shutter speed often, this are something you can do:
    1. use a higher F value
    2. use a lower iso film, or digital cam you can set.
    3. fix on a ND filter when you need it.

    hope it helps.
    cheers=p

  7. #7
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    Quote Originally Posted by CYRN
    I wonder that with digital,,, does the ISO setting change if limits have been reached?
    It does if you set ISO to AUTO.

  8. #8

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    Quote Originally Posted by Jus_a_Nick
    View it as this way:
    P: Full Auto
    S: Half Manual
    A: Half Manual
    M: Full Manual

    In S mode, it shutter prioity. You adjust the shutter speed and the camera adjust the aperture to gives you the correct exposure*
    In A mode, it aperture priority. You adjust the aperture and the camera adjust the shutter till you get a correct exposure*
    In M mode, it full manual, you adjust both the shutter and aperture.
    Sorri, i dunno abt P mode though.

    *correct exposure: this so call correct exposure is wat is deem correct by the camera metering. however wat is deem correct by the camera might not always be correct. This is one of the reason why you use a EV compensation. i,e when metering against a scene of snow, your camera might actually gives you a higher reading then it should be, thus giving you a greyish instead of a pure white snow when you follow the 'correct exposure' thus we actually use a compensation of +1- +2 to compensate for the flaws of the meter.




    by setting a compenation of -1 would actually require you to use a higher shutter speed which your camera already cannot support.
    if your qns is the oppz, in the case of putting your compensation to + , true, it will let you take w a slower shutter speed, and if this falls within your camera supported shutter speed, you can take the shot. but wat will happen?
    unless you know wat you are doing, by using using a + compensation you are actually overexposing your shot, and rendering the subject you meter to become overexpose. In general this should not be the way to do when your camera hit the highest shutter speed.

    in general, i would personal feel tat seldom would you hit the highest shutter speed, unless you using a very high speed film in daylight, or shooting with 1.4, or shooting at the sun.
    if you do have the prob of hitting the highest shutter speed often, this are something you can do:
    1. use a higher F value
    2. use a lower iso film, or digital cam you can set.
    3. fix on a ND filter when you need it.

    hope it helps.
    cheers=p

    That's a good one.

  9. #9

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    Quote Originally Posted by Sgt. Pepper
    That's a good one.
    thanks dude=p

  10. #10
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    Quote Originally Posted by Jus_a_Nick

    *correct exposure: this so call correct exposure is wat is deem correct by the camera metering. however wat is deem correct by the camera might not always be correct. This is one of the reason why you use a EV compensation. i,e when metering against a scene of snow, your camera might actually gives you a higher reading then it should be, thus giving you a greyish instead of a pure white snow when you follow the 'correct exposure' thus we actually use a compensation of +1- +2 to compensate for the flaws of the meter.
    one question...

    how would one know whether the camera metering is wrong at that particular moment of shoot..?

    taking that you are using film and don't have the benefit of viewing the picture at once...!

  11. #11

  12. #12

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    Quote Originally Posted by SuRfTeC
    one question...

    how would one know whether the camera metering is wrong at that particular moment of shoot..?

    taking that you are using film and don't have the benefit of viewing the picture at once...!
    the link by pepper is an informative read. to add on to that, you can compensate the sunny16 rule by how strong the sunlight and how cloudy it is.
    I have seen many exp photographer that can tell by jus looking at the sky that it is a cloudy F11, or cloudy F8
    if you are not one of those who trust by eyes, and prefer to be more gadget wise, you can also try the following:
    1. use your camera to meter on a grey card that have the same direction of light falling on your subject.
    2. meter using a incident light meter .
    (well, of course it assumes your meter is well calibrated)

    hope it helps, cheers =p

  13. #13
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    Quote Originally Posted by ckiang
    IF you are in Av, camera does it by altering shutter speed.

    If you are in Tv, camera does it by altering aperture.

    If you are in P/Auto/preset/scene modes, the camera follows it's own algorithm.

    If you are in M, and you don't follow meter, exposure compensation has no effect.

    Regards
    CK

    And to add to that, exposure compensation doesn't do anything in A mode if your camera keeps to the 1/focal length rule and u are at the shutter limit (in low light it seems to be usually 1/60sec). I.e it will not drop below 1/60sec in low light. If u use flash, then it seems like it usually alters the flash coverage. At least that is what I see on my Dynax 7 + 5600HS.

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