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Thread: Underexposure

  1. #1

    Unhappy Underexposure

    Have been trying to freeze fast moving object with fast shuttle time (1/125 etc) but usually my shots turn out to be underexposured even though I step up the exposure compensation.

    Wat are the soultions to solve this problem, is it thru adjusting the aperture (aperture priority)?

    Pls advise, will appreciate greatly.

  2. #2
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    Digital or film camera? What's your ISO speed in relates to your aperture and shutter speed. Prehaps you can try increasing your ISO setting or aperture?

  3. #3

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    mine is digital
    using ISO100

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  5. #5
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    Underexposure can only be due to not enough light available for that combination of aperture/shutter speed/sensitivity of medium.

    By using shutter speed priority you probably used a speed that may be able to stop the action/movement but you must not forget that the camera will automatically open up the aperture to get a correct exposure. If your lens aperture has reach its limits (can't be opened up any further to accommodate that speed) then you are in trouble, the result is underexposure. By playing with the exposure compensation you are increasing the chip sensitivity, but this one also has its limits. You likely ran into the limitations of the camera's aperture and chip sensitivity.

    Hong Sien
    Last edited by hongsien; 27th June 2003 at 04:33 PM.

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    Originally posted by hongsien
    By playing with the exposure compensation you are increasing the chip sensitivity, but this one also has its limits.
    Exposure compensation does not alter the chip sensitivity. The ISO setting alters the chip sensitivity or rather the gain.

    I agree with djchris, use a flash if there is not enough light to sustain the shutter speed.

  7. #7

    Default Re: Underexposure

    Originally posted by tangoninazero
    Have been trying to freeze fast moving object with fast shuttle time (1/125 etc) but usually my shots turn out to be underexposured even though I step up the exposure compensation.

    Wat are the soultions to solve this problem, is it thru adjusting the aperture (aperture priority)?

    Pls advise, will appreciate greatly.
    Not sure what's your subject.

    Fast shuttle speed can be gained by using a bigger aperture eg. f2.8 wide, f4.2 tele, if that is still not enough, try ISO200 or use a flash (fill-in).

    If it is outdoor photoshoot, a good nice weather helps.

  8. #8

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    Thanks for all the advises
    keep them coming. More info means more learning experience

  9. #9
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    Originally posted by linse
    Exposure compensation does not alter the chip sensitivity. The ISO setting alters the chip sensitivity or rather the gain.

    I agree with djchris, use a flash if there is not enough light to sustain the shutter speed.
    On my older casio QV-3000 when I change the exposure compensation, it increases sensitivity. There is no ISO dial on my casio, it is basically the same. It is the same for film cameras: when you change the ISO dial or use exp compensation, it is the same.

    Not sure about those DSLR cameras.

    Hong Sien

  10. #10

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    Originally posted by hongsien
    On my older casio QV-3000 when I change the exposure compensation, it increases sensitivity. There is no ISO dial on my casio, it is basically the same. It is the same for film cameras: when you change the ISO dial or use exp compensation, it is the same.

    Not sure about those DSLR cameras.

    think there is something amiss with the concept. When you rate the ISO setting or use exp compensation on a film camera, you are not changing the sensitivity. The film loaded in the camera body is still of the same sensitivity, obviously. What you're doing is an effect of compensating of the camera's metering. Virtually, it can be seen as changing the "sensitivity" as in you may get faster or slower shutter speed, but physically, sensitivity of the film definitely isn't altered.

    As for digital cameras, you only change the sensitivity of the CCD when you change the ISO setting. Note this is NOT the same as rating the ISO on the film camera. On the digicam, you are physically asking the chip to increase gain thus have a higher sensitivity. On the film camera, you are just overriding the camera's perception of what is sensitivity of the film it is using. Arguably, the conceptual end product of both may be the same, but physical process wise, they are fundamentally different.

  11. #11
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    Just to add ...

    when you use positive exposure compensation, you are telling the camera to overexpose the photo. It does so by slowing the shutter speed or opening up the aperture so more light photons will hit the CCD or film, therefore resulting in a brighter or more exposed photo.

    When you increase the ISO or gain in digital cameras, the camera amplifies the signal from the same number of light photons hitting the sensor to make a brighter image. Unfortunately, noise is amplified as well therefore you have lower signal to noise ratio. That's why higher ISO settings in digital cameras are more noisy.

    Therefore, if you just use negative exposure compensation to increase the shutter speed without altering the aperture, you will underexpose you photo.

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    Ah! ok, thanks! So, digitals don't work the same as film cameras in this (compensation)? How about if I use my casio at fully manual: I set speed and aperture and then use compensation? I will have to try it.........what I meant was that on film cameras when you change the ISO or compensation they are doing the same on the camera (changing the metering) whereas it seems in digitals you change the gain in one way and change the aperture/speed setting in the other. I still haven't figured it out on my old casio if that is the case, but it must be according to the digital experst here......

    Hong Sien
    Last edited by hongsien; 28th June 2003 at 02:02 PM.

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    Originally posted by hongsien
    Ah! ok, thanks! So, digitals don't work the same as film cameras in this (compensation)?
    Digital and film cameras work the same way when you use exposure compensation because it involves the camera's metering.

    How about if I use my casio at fully manual: I set speed and aperture and then use compensation?
    If you use any camera on manual exposure: Assuming the shutter and aperture are set for the correct exposure to start with, if you then dial in positive exposure compensation, the camera's metering will then indicate that the scene is underexposed. In turn you will have to decrease the shutter speed or open up the aperture to match the new metered exposure.

    I will have to try it.........what I meant was that on film cameras when you change the ISO or compensation they are doing the same on the camera (changing the metering) whereas it seems in digitals you change the gain in one way and change the aperture/speed setting in the other.
    It is true changing the compensation and ISO on a non-digital alters the metering. However, this does not make you film more sensitive to light unless you push process the whole roll of film. If you haven't being push-processing your film and is using negative exposure compensation/increase ISO settings to increase the shutter speed in low light situations, you have been underexposing your negatives. It may not be obvious to you if the photo labs have compensated for the underexposure. However, if you shoot slides, it will be very obvious. You can underexpose film more and still get away with it as film has a greater lattitude compared to CCD/CMOS chips.

  14. #14

    Talking

    Originally posted by linse

    If you use any camera on manual exposure: Assuming the shutter and aperture are set for the correct exposure to start with, if you then dial in positive exposure compensation, the camera's metering will then indicate that the scene is underexposed. In turn you will have to decrease the shutter speed or open up the aperture to match the new metered exposure.
    how izzit pozzible when, in manual mode, u dail in +ve expozure compenzation but yet the camera'z meter will then indicate underexpozure ..... ?? .....

    izzit bcoz the camera meter will take the compenzated setting az the correct setting ..... ?? .....

    thankz .....


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    Originally posted by FOOXX
    how izzit pozzible when, in manual mode, u dail in +ve expozure compenzation but yet the camera'z meter will then indicate underexpozure ..... ?? .....

    izzit bcoz the camera meter will take the compenzated setting az the correct setting ..... ?? .....
    Sorry if I am confusing anyone. Say if the initial exposure of F2.8 1/125 (manually set) gives the correct exposure. The camera's meter will indicate underexposure (when using +ve exposure compensation) relative to the initial setting (0 exposure compensation).

  16. #16

    Talking

    Originally posted by linse
    Sorry if I am confusing anyone. Say if the initial exposure of F2.8 1/125 (manually set) gives the correct exposure. The camera's meter will indicate underexposure (when using +ve exposure compensation) relative to the initial setting (0 exposure compensation).
    hmmm ..... ok .....

    so letz say the initial correct setting iz f2.8 1/125 .....

    now me over-compenzate by 1 stop .....

    so now the camera meter will "think" that f2.8 1/60 iz the correct expozure n a setting of f2.8 1/125 will underexpoze the shot .....

    iz thiz explaination correct ..... ?? .....

    thankz .....


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    Yes.

  18. #18

    Talking

    Originally posted by linse
    Yes.
    thankz .....


  19. #19
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    Originally posted by linse
    Digital and film cameras work the same way when you use exposure compensation because it involves the camera's metering.


    If you use any camera on manual exposure: Assuming the shutter and aperture are set for the correct exposure to start with, if you then dial in positive exposure compensation, the camera's metering will then indicate that the scene is underexposed. In turn you will have to decrease the shutter speed or open up the aperture to match the new metered exposure.


    It is true changing the compensation and ISO on a non-digital alters the metering. However, this does not make you film more sensitive to light unless you push process the whole roll of film. If you haven't being push-processing your film and is using negative exposure compensation/increase ISO settings to increase the shutter speed in low light situations, you have been underexposing your negatives. It may not be obvious to you if the photo labs have compensated for the underexposure. However, if you shoot slides, it will be very obvious. You can underexpose film more and still get away with it as film has a greater lattitude compared to CCD/CMOS chips.
    Thanks! I know all this, but I am confused with exp compensation in digitals and increasing gain, I am not sure how to do that (increasing gain) on my Casio QV-3000. Anyone who can help me? I also read somewhere that the Casio QV-3000 can be used fully manual but can't seem to find out how to do it. Will have to read dpreview I guess. Thanks anyway!

    Hong Sien

  20. #20
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    Ok, have been playing with the Casio abit more now, and I finally found out what happens with the compensation and how to increase the gain! Damned electronics!

    Hong Sien

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