This post is a continuation in the series of “Correct Exposure” series. We will deal with “exposure compensation” in this post, and it’s best that you’re familiar with what we’ve covered in my earlier tutorials, in particular the first two parts in this series, (click here and here for a refresher, if needed).
On to the subject at hand… what is “exposure compensation”? In simple terms, one can describe exposure compensation as being a man-made “interference” with the camera’s decision-making process. As you might recall from my previous post, the exposure meter is a gauge that tells you the extent of brightness or darkness being recorded in the image, and whether or not your image should be exposed properly, or correctly, given the selected settings (aperture, ISO, shutter). The way the camera “decides” this is to make a computation on the basis of the light that is coming into the camera. This computation is designed in a way to show a “correct exposure” reading if the light coming into the camera produces a particular shade of grey if it is “mixed” together. If the result is a darker grey, the camera indicates that the image is underexposed, and if it’s brighter, it shows an overexposed reading. Where does our interference come in then? How can we introduce exposure compensation, and why would we want to?
For starters, let’s clarify one thing. The camera, on its own and irrespective of how good it is, is no guarantee of a good photo. It is almost insulting to a good photographer to be told “wow, that’s a great photo – you must have a good camera.” Why? Simple really – no camera on its own can take a good picture. You need a photographer, and, preferably, one that knows what he or she’s doing. One area where this really matters is in knowing when the camera’s exposure meter is “lying” to you. In such circumstances, one needs to “compensate” for this lie, by overriding the camera’s decision. Let me present you with an example.
Suppose you’re taking a picture of a dark object placed on a dark background. In such a situation, much of the light coming into the camera is going to be dark. In fact, most times, it will be so dark that if you mix all the light (and colour) coming in, the result would most definitely be a grey that is darker than that required for a “correct exposure”. In such situations, if you DO take a picture based on the camera settings recommended by the exposure meter, your image would end up looking much brighter than what is in truth the real situation. In such situations, you need to tell the camera that you need an underexposed image, and this is done by using the exposure compensation button/dial on your camera. (Most cameras allow you to do it, refer to your camera’s guide for more specific instructions). By telling the camera you need to underexpose, the settings recommended by the camera are adjusted to let less light in, generally resulting in a more “true” photo of the subject than if you had used correct exposure. Check the images below, for instance.
The image on the left is what the camera “suggested” would be a correct exposure of a black joypad on a black laptop case. As you can see, there’s very little “black” in the image, despite both items being black in colour. When I took the photo on the left, the exposure meter read “zero”, but does that imply that the camera was right? Would the manufacturer of the joypad be happy that his product is shown as grey when in fact it is black? I doubt that. That’s why I had to use exposure compensation. On the right, I used a 3-stop, negative exposure compensation, and the ISO was lowered to 400, (which is one half, of one half of one half of 3200, the original setting). The image, obviously, turned out much darker, but at least it’s definitely more correct than the “correct exposure”, right?
The same principles apply when photographing a scene or subject that is made up of a lot of white/bright elements – but this time round the exposure compensation should be on the plus side – that is, you need to tell the camera to let in more light so that you end up with the proper exposure needed. Examples include a photo of a white subject on a white table, for instance – with so little grey or dark items showing, the resulting picture would definitely be an underexposed image if you use the camera’s recommended settings. By dialing in some positive exposure compensation, you will get a better image for sure.
So, to recap:
- The Correct Exposure is sometimes not ideal – for very dark scenes or very bright scenes you will probably need to use exposure compensation.
- When shooting a scene that is predominantly dark, use negative exposure compensation.
- When shooting a scene that is predominantly bright, use positive exposure compensation.
Finally, using exposure compensation is only possible when you’re shooting in Aperture Priority, Shutter Priority or Program exposure mode. When using Manual exposure mode, you control all three factors of ISO, Aperture and Shutter Speed and thus need no “compensation” per se – you just have to change the settings you want to get the image exposed to whatever level you want it. Under the other modes however, exposure compensation is used as described above, to tell the camera to over or under expose the image as desired. We’ll cover “exposure modes” more in depth in my next post if you want more detail!