Exposure Compnesation - Plus or minus for bright and dark subjects

Discussion in 'Beyond the Basics' started by ted_smith, May 8, 2007.

  1. ted_smith

    ted_smith TPF Noob!

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    Hi

    I'm getting horribly confused about exposure compensation.

    My Nikon D70's user manual says "as a rule of thumb, positive compnesation may be needed when the main subject is darker than the background, negative values when the main subject is brighter than the background". That makes sense to me.

    However, I've just read a book where it uses the example of photographing black dogs and, by contrast, white dogs. It's in the chapter titled 'Working with extremes of exposure'. It says when photographic black dogs "If your camera allows exposure compensation try subtracting 1 stop" and when photographing white dogs "If your camera allows exposure compensation try adding 1 stop".

    The two totally contradict each other? I've searched the net and everything I read suggests that the manual is correct but I also doubt the book is wrong and I expect I have simply mis-understood but I don't know what I have mis-understood. Can anyone clarify?

    Thanks

    Ted
     
  2. Sw1tchFX

    Sw1tchFX TPF Noob!

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    Your meter will try to make the dogs grey, so for the black dog, you need to underexpose to make it black again and over expose the white dog to make it white again, same goes for things like snow.
     
  3. gizmo2071

    gizmo2071 TPF Noob!

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    As switch said, your lightmeter will try to expose the colours for 18% grey.
    And a black dog or white snow isn't going to be 18% grey.
    So you need to adjust the exposure accordingly.
    Something thats not that simp[le to explain, but something that you show have a go at. Shot some white/black objects in sunlight. Go by the exposure reading and see how they look, then over/under expose to get them to look how they should.
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Both explanations make sense to me and I think I see where the confusion is.
    In this example, the subject is darker which means that the background (presumably the larger part of the image) is brighter...and brighter scene means you add exposure.

    Same thing here. The advice giver is assuming that the subject is smaller than the background and that you are using some sort of evaluative metering. The background is what is influencing the meter most...so that is what you use to adjust the exposure. If the background is darker...subtract exposure.

    That's correct...but in this example, we are metering the subject...not a small subject on a larger background. To do this, either fill the frame with your subject when you meter...or use the centre/spot metering mode.

    The whole idea behind this, is that the camera's meter want to turn everything into middle (18%) grey. It wants to turn snow grey and it wants to turn a black dog grey. When using exposure compensation, you are looking at the scene and trying to determine if the camera's meter will get it right or wrong. If the scene is a perfect mix of light and dark tones...then middle gray will probably be a good choice...no compensation needed. However, if the scene is bias one way or the other...then you need to realize that it will fool the meter and you should compensate. Going back to the dogs...a white dog will make the camera think it's too bright and it will try to give an exposure to make the dog grey....so you have to add exposure to get it back to white. Bright scene...add exposure. With a black dog, the camera with think it's too dark and will give too much exposure...so to get it to look black, you need to subtract exposure. Dark scene...subtract exposure.

    It can take a while to wrap your head around the concept...but once you do...it's all good.
     
  5. gizmo2071

    gizmo2071 TPF Noob!

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    Another thing you need to consider is the type of metering that you camera uses.
    Spot meter would be the most ideal as you could see what it recommends for specific areas of the scene.
    Where-as average or matrix metering is giving an average exposure reading for the whole scene, which is not what you want for this specific task.

    Sorry to add another problem to your understanding of this subject :p
     
  6. ted_smith

    ted_smith TPF Noob!

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    First things first, thanks everyone for your help with this, especially Mike_Mike who has taken some considerable time to make his point clear and I think I have more or less understood.

    Can I test and you guys tell me if I'm wrong :

    Dark black background and a dark dog - decrease exposure
    Normal background and a dark dog - decrease exposure, consider centered metering as opposed to Matrix to seperate dog metering from background metering
    Normal Background and a normal coloured dog - no exposure adjustment (probably)
    Normal background and a white dog - increase exposure, consider centered metering as opposed to matrix
    Bright background, bright white dog - increase exposure.

    And in summary, would I be wise to memorise Big_Mikes summary? :

    Dark Scene - Decrease Exposure (Double DD!)
    Bright Scene - Increase Exposure


    Ted
     
  7. Digital Matt

    Digital Matt alter ego: Analog Matt

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    I think you have a good basic understanding. What will really cement things is to go out and shoot. You have a digital. You can get instant feedback. Bracket your shots. Take one at the meter's recommended exposure, and change the exposure comp in both directions. View the pictures on the computer and view the Exif info. It's the only way to understand what is happening.
     
  8. Mike_E

    Mike_E No longer a newbie, moving up!

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    Or you could study Ansel Adams' zone system and use a spot meter with manual exposure and not ever worry about it again. ;) (be aware that to do this you have to be really sure of your composition)

    mike
     
  9. Garbz

    Garbz No longer a newbie, moving up!

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    What you should do is go take pictures and then while viewing them on your monitor take note of the brightness and metring used.

    Matrix Metering on Nikons as well as Evaluative Metering on Canons uses some complex guesswork to what you are trying to achieve. I have had plenty of occasions where I was photographing an average subject (which I will define here as a tanned person) against either a black or a blow out white background, and the matrix metre has hit it spot on. The reason for this is that in matrix metering the most weight is given to the assumed subject (i.e. the object in focus) which in this case ignored the background because of very large differences in focus (38cm vs infinity).

    I make a suggestion if you can not figure out your matrix metre and know how it will behave in varied situations (I have after 5 months of constant use and battles with it), switch to either centre weighted or spot metering. These modes are very predictable, and I know photographers who just look through their view finders with centre weighted turned on, take a second to adjust the EV compensation, and hit it dead on first go.
     
  10. Torus34

    Torus34 No longer a newbie, moving up!

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    Based on your original post, I suspect that the author of the second citation was guilty of sloppy wording. If you understand his instruction of 'subtract one stop' to mean reducing the f number by one value [f8 to f5.6, eg], both citations say the same thing.

    You might find the discussion of exposure in the following article to be of interest:

    http://www.thephotoforum.com/node/47
     
  11. EOS_JD

    EOS_JD TPF Noob!

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    To reduce exposure by one stop this is one of three ways in which to do it. Halving the shutter speed or halving the ISO are the others. Using EC it's usually done by shutter speed or aperture.

    Sometimes you don't want to affect the depth of field so this is why the writer used the expression one stop when refering to EC as it can be done in 2 ways (discounting ISO being used for EC) and he assumes you know the basics of what one stop is.
     

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