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Thread: Exposure correction questions.

  1. #1

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    Exposure correction questions.

    So now that I have my new camera, I started reading on how to improve myself as a photographer and how to control my new toy.

    So far so good, I understand correctly the role of the Shutter Speed, Aperture (Not everything from it, but the basic), and the ISO.

    After reading quite a few tutorials here, I found out about "Exposure". How to have a good expore not to clip off some highlights etc.

    Some questions remain regarding Exposure and Compensation.

    1. The way I understand Exposure compensation is a built-in camera setting that is "applied" when you focus by the camera itself. Sometime it is possible that the camera might applied it wrong in some scene the light is a bit tricky (Depending on the evaluation mode). Am I right?. Also why is it overexposing, because my setting in manual mode wasn't getting enough light to take a good picture?

    2. How do I read the Exposure meter in my viewfinder (Canon T3). When it's on the right of the middle it means that the camera is overexposing? But does it mean that my photo will be washed out? Do I have to keep this indicator in the middle? Or is it an indication of the level of light I'll get with my current setting if I take my picture.

    3. Is it possible to over or under expose myself the shot? (without changing the shutter speed, aperture and ISO)? I tought that was the use of the EV+- on my camera. When people say over expose your picture, how do I do it? (Shutter, Aperture, ISO?) or there are other way.

    If you have any other additional information, feel free to share, because I'm stuck here

    Thank!

  2. #2

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    Re: Exposure correction questions.

    The principles are quite simple, Mathieu, but actually understanding and then explaining them to someone else is a lot trickier.

    Basically, using an auto exposure setting (and I include the semi auto options like Tv or Av here) will correctly expose a perfect scene under perfect conditions.

    The problems usually occur when there are a few 'hot spots' or deep shadows which the auto exposure meter just doesn't see. This is where you can be 'cleverer than the camera' and use a little bit of exposure compensation to correct for the camera errors.

    The knack is recognising where/when these anomalies are likely to occur, which comes with practice.

    I'm not familiar with that camera, but does it also have a spot metering option? If so, try spot metering around a mixed lighting scene. Select some obvious hot spots and deep shadows and note the readings which will vary considerably.

    Evaluative metering (which goes by other names on different cameras) tries to work out an average but there are only a limited number of 'metering zones' available to your meter. Which is why it sometimes misses something obvious.

    Compare your spot readings with the evaluative reading.

    Ideally, under perfect circumstances, keeping your meter needle in the middle should produce a perfect result. But in reality, you often have to make a few manual adjustments by setting a little positive or negative Exposure Compensation.

    This will work in all of the semi auto options, except for full manual of course.

    Other potential problems come with techniques like focus on a particular point, hold the focus, then recompose the scene. With some settings, the exposure is held at the original focus point while other options will take a new exposure reading when you recompose your shot. Using exposure lock can sometimes be needed.

    But this is starting to move onto a bit of a specialised field now.

    In reality, you probably just need to do a lot of experimenting, and take notes, until everything eventually starts to make sense. Like I said, it isn't that difficult; but it can take a bit of initial understanding.

    Does this help; or have I just rambled on as usual?

  3. #3

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    Re: Exposure correction questions.

    Hey Geoff, Thank for taking the time to help me understand. Yes everything was clear but the "adjustments by setting a little positive or negative Exposure Compensation" you talk about.

    In Semi-auto mode, setting the Exposure Compensation will either move the Shutter, Apperture or ISO, depending on which semi auto mode you are, am I right? Exposure compensation is made of the combination of the three, it's not another setting apart of these three right?

    And yeah my camera support spot.

  4. #4

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    Re: Exposure correction questions.

    Yes, putting it very simply, if you are using the Tv (shutter priority) option you choose the shutter speed (and ISO) and the camera automatically picks the aperture. So using a bit of exposure compensation will tell the camera to select a slightly different aperture. And this will, hopefully, give the correct exposure for the scene.

    The same thing happens with Av (aperture) except that the shutter speed changes slightly.

    You can use an auto ISO but I prefer to keep that as a non variable part which I will manually alter if I can't get what I require with the current settings. Choosing the best ISO is something else which needs to be learned but basically, try to keep the ISO fairly low but don't let it dominate other requirements.

    It all seemed a lot more complicated with film cameras; particularly those old models without an in built exposure meter. You just had to guess the correct settings based on experience. Or use a hand held meter and hope that your camera settings requirements and the meter readings produced a similar result.
    Last edited by Geoff F; 16th June 2011 at 08:55 PM. Reason: spelling.

  5. #5

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    Re: Exposure correction questions.

    Great thank.

    So basicly "Exposure compensation" is not another settings that modify the result of the shot, but rather a concept "how much more or less light will you let enter your camera vs the camera light reading" using the Shutter speed, Aperture and ISO.

    Am I right?

  6. #6

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    Re: Exposure correction questions.

    Let's give a practical example, Mathieu.

    If I set my camera to Av mode with F8 and get a shutter speed of 1/200 then dial up an Exposure Compensation of +1 my shutter speed becomes 1/100. Which means a 'brighter' photo. Or the reverse for negative compensation.

    I could achieve the same result with the manual settings but using EC allows my settings to 'update' automatically as I move my camera around the scene; or the light changes.

    But when EC is applied your photo will always be brighter (or darker with negative compensation) than the normal zero setting would have been.

    This is most useful when the camera meter is being fooled by an unusual scene. For example a black cat sitting in the snow.

    Have a read of this CinC tutorial

    http://www.cambridgeincolour.com/tut...a-exposure.htm

  7. #7
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    Re: Exposure correction questions.

    Hi Mathieu,

    Quote Originally Posted by kontrol View Post
    Great thank.

    So basicly "Exposure compensation" is not another settings that modify the result of the shot, but rather a concept "how much more or less light will you let enter your camera vs the camera light reading" using the Shutter speed, Aperture and ISO.

    Am I right?
    Basically 'Yes', Exposure Compensation, or EC for short, is an 'offset' applied to what the camera wants to do and it adjusts either the shutter speed, aperture or ISO, it isn't a fourth type of setting. As Geoff has said, it only applies in Auto and Semi-Auto, not Manual.

    To be pedantic, your "how much more or less light will you let enter your camera vs the camera light reading", isn't 100% accurate - when we adjust ISO, which is adjusting the senstivity of the sensor to light, it isn't affecting the light entering at all, but I'm splitting hairs.

    Which of the many methods (Tv, Av or M) of exposure control is "right" depends on the subject, the light and the background. By "right" I mean most likely to give consistently correct exposures on multiple shots - I shoot wildlife, where this choice is very important. But for landscape, typically with the camera on the tripod, unless clouds are frequently rushing across the sun, or it is sunset/sunrise, you usually have many minutes in which to assess meter readings and set a good exposure usually in Manual mode, for the one shot - how sedate!
    Ooops, did I say that out loud? now I've upset half the members

    Cheers,

  8. #8

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    Re: Exposure correction questions.

    Awesome answers guys. Now I understand correctly the concept Thank.

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