[yelvertoft]

Having posted a thread on the basics of manual exposure mode, I thought I’d put together another beginner’s article on another exposure feature, “Exposure Compensation”.

To begin, it’s worth noting that a camera’s exposure meter monitors the amount of light entering the camera (the days of non-TTL metering are long gone in this digital era). Sounds obvious I know, but it should be remembered that it’s simply measuring the amount of light, not the colours. Despite all the technology that’s gone into cameras these days, cameras cannot interpret what they see, that is down to the user. The camera’s light meter detects a certain amount of light and it doesn’t know if this is a dark surface with a lot of light falling on it, or a light surface with a small amount of light falling on it. To cope with this uncertainty, the meter in the camera will be calibrated to give the correct exposure when it is measuring the light reflecting off a mid-grey surface.

So, if you take a picture of a completely black surface and nothing else, left to its own devices, the camera will tend to give settings that would result in more of a dark grey than black. Likewise, if you take a picture of a completely white surface and nothing else, the camera will give settings that will tend towards light grey rather than white. In each case, the camera does not know that the surfaces are plain black or white and the meter is calibrated so that it hedges its bets on grey.

Ok, the photographer isn’t so clueless about what he or she is looking at. The photographer knows they are looking at a black or white surface. Knowing this, and knowing that the meter is calibrated to assume everything is mid-grey, when faced with a scene with lots of bright/dark areas, the exposure compensation feature can be used to, errrmmm, compensate the exposure.

If you want the brighter areas of a scene to be remain bright in the picture, the compensation control should be used to give a positive compensation. If you want the darker areas of a scene to remain dark in the picture the compensation control should be set to a negative value. You know the camera will try and turn everything to grey and are telling it to keep the whites white (positive compensation) or the blacks black (negative compensation). If the scene is an equal mix of light and dark, assuming you are using an evaluative exposure metering mode, the camera will get things pretty much right on its own as it averages things out.

Scenes that will get it wrong would typically be snow scenes or where the subject is in shade against a bright background (positive compensation needed), or alternatively a light coloured subject against a very dark background (negative compensation needed).

How much compensation to apply will vary depending on the lighting, subject and background but +/- 1.0 is not at all unusual. Remember, with digital, it costs nothing to try a range of different exposures so fire away with a range of different settings and see what the results are like. Examine the EXIF data of each shot and learn the effect that each level of compensation gives. Many cameras have an “auto-bracketing” feature where a range of (typically) 3 shots can be taken, the camera automatically applying “correct” and a degree of under/over exposure compensation to the next three shots taken. This is a useful feature to help you learn the effects of under/over exposure and to help understand the meter readings your camera will have taken.

Hope this helps someone out there who is struggling with their new Christmas toys.

Regards and happy Christmas to everybody,

Duncan.