Need some explanations about exposure compensation

Discussion in 'Photography Beginners' Forum' started by Tom3, Dec 8, 2008.

  1. Tom3

    Tom3 TPF Noob!

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    I need to understand something:

    the exposure being a combination of the ISO, shutter speed and aperture, at which point does the exposure compensation work?

    Is it merely post processing from the original data before being saved to jpg? I havent' tried but, in that case, does it even do something to the raw picture?
     
  2. rufus5150

    rufus5150 TPF Noob!

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    Exposure compensation depends on what mode you're in. (The following assumes you're using a fixed ISO because I've no idea how auto-iso works.)

    If you're in Aperture priority, adjusting the exposure compensation will increase or decrease the shutter speed.

    If you're in Shutter priority mode, adjusting the exposure compensation will increase or decrease the aperture.

    If you're in 'P' mode (on canon cameras, at least), it will try to recalculate both the aperture and shutter speed to maintain its 'optimal' parameters for getting you a reliable shot.

    It is definitely not done after the image has been captured. It directly affects your exposure settings when the image is taken.
     
  3. Turnerea

    Turnerea TPF Noob!

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    It depends on what mode you are in. Assuming you aren't using some function that allows auto-ISO, then your ISO is set. Then if you are in Av (aperture priority) the camera takes your exposure compensation into consideration when calculating the shutter speed. The same, but just switched for Tv (shutter priority). In manual exposure compensation is not used, as you are choosing both aperture and shutter speed... and the ISO is set as well. So you basically dial in whatever compensation you'd like in manual, hence its flexibility...
     
  4. kundalini

    kundalini Been spending a lot of time on here!

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    The bold above is incorrect. The camera is trying to meter for 18% grey. If you're shooting snow or coal (in manual), then if you don't add or subtract (+/-) compensation, then each subject will be grey.

    Basically, if your subject is darker than the background, add EV (+) and likewise in reverse, take away EV (-) if your subject is brighter than the background.
     
  5. rufus5150

    rufus5150 TPF Noob!

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    I don't even have a way to get to the exposure compensation values when I'm in manual mode. The main wheel modifies the shutter speed, the shift-main-wheel modifies the aperture. I can certainly under-expose or over-expose in 3rds of stops, but the EV just becomes a process of reading the meter.

    Other cameras may differ, but that statement is certainly true for mine (rebel xti)
     
  6. tsaraleksi

    tsaraleksi TPF Noob!

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    While this is true, a lot of people get confused about the use of EC in manual mode, not really understanding the way that the you have to simply pick the exposure you like best, as opposed to the way it works in the other modes.
     
  7. kundalini

    kundalini Been spending a lot of time on here!

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    Sorry rufus...... shudda stated this was for a Nikon, but I figured the functionality was universal. My bad.
     
  8. Tom3

    Tom3 TPF Noob!

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    so, if I understand correctly, it merely change whichever setting is not locked, in all modes but manual, in order to adjust the exposure.

    however, I do not understand what happensa in manual? i guess it could change the iso settings, but what does it do if everything is manual, incuding iso?
     
  9. Photog

    Photog TPF Noob!

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    Now I'm confused! In manual mode then, if your camera has an option to change EC, surely this is effectively just changing the calibration on the meter - shifting it left/right, and then you are the one who compensates for this different metering by adjusting shutter speed/aperture? Yes/no?
     
  10. Turnerea

    Turnerea TPF Noob!

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    Maybe this functionality is different in Nikon, but the fundamentals will remain the same.

    In manual mode you have full control, so you can get the same results of having used exposure compensation with Av or Tv, but you're not really using it "exposure compensation"- you are dialing in whatever exposure you want directly- not compensating a definite number + or - from the reading like you do in Av or Tv mode.

    To the original poster- your statement about what happens in Av and Tv is correct- just adjust the one you aren't setting. Hope this helps clear up what happens in Manual... I'm an engineer too... I think about it this way- when I'm using exposure compensation that's one equation used to pin down the three variables (aperature, shutter speed, iso). When in manual you don't have this equation relating aperture+shutter speed, so you need to dial in both the aperture AND shutter speed to make up for losing one equation....
     
  11. Kegger

    Kegger TPF Noob!

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    I just use it to tone down exposure on my camera, as it shoots to the left as it is. So -.07 EC evens everything out. So you can look at it as a fine tune for the sensor.
     
  12. Tom3

    Tom3 TPF Noob!

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    ok, this seem to make sense now.

    I'll do some tests to see what it does in full manual; maybe it doesn't do anything then on my camera (Nikon D200)
     

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