Exposure Compensation Setting
Exposure Compensation is an intentional exposure adjustment away from the light meter reading exposure that your camera has provided, for the purpose to arrive at your desired exposure.
Camera light meters have some draw backs reading the light of the scene. They do a great job of averaging the many different luminance areas of light and dark, but they don't have the capacity to understand the predominantly bright or dark reflective scenes.
That is to say, they tend to over exposure dark scenes and under exposure light scenes. So to get the exposures nudged into the right luminance range requires an analytical interpretation and adjustment to the exposure of the scene from you.
There is also the subjective side of your interpretation of the scene, for which the light meter is going to have no clue on how you want this scene to look
The light meter sees objectively, attempting to provide a averaged reading of light and dark areas of your framed scene, what's more, the light meter is designed to read only the middle tone value correctly.
So incorrect exposures are more frequent than you might want to expect from your expensive camera purchase, don't worry, this is rather common and you can learn to read from the scene what you want, recognize the light meter's limitations and then apply the correct through the use of Exposure Compensation.
Exposure Compensation is a great feature to use for making exposure adjustments away from the light meter's interpretation of the scene. In fact I would say it's design is brilliantly simple and intuitive.
We generally learn over time how and when the light meter will fail in it's interpretation of of the scene, I help you speed up that process by showing you what is going on, and how to avoid it in the section Understanding Exposure.
Exposure Compensation Overview
Let's assume you already have your exposure reading for a scene. You are using an automated exposure mode of AV or TV of your choice. You take the picture but you find the exposure appears lighter or darker than you desire to be.
The Exposure compensation dial is likely the big wheel dial on the back of your camera. It will adjust the Aperture setting if you are currently set to using TV or Shutter Priority semi automatic mode on your camera. The Exposure Compensation dial will adjust Shutter Speed settings, if you are using a AV or Aperture Priority semi automatic feature.
The Exposure Compensation display will look similar to the graphic below.
Exposure Compensation - Photopursue.com © 2011.
Exposure Compensation units have a maximum range limit of adjustment of ±2 stops of light, and stepped in 1/3 stop increments.
An important Exposure Compensation Basic
The exposure compensation indicator (the long pointy thing I show in the middle of the diagram) is seen in your camera veiwfinder and shows you the deviation you are from the light meter reading
The light meter reading is what I often call the base exposure. As you adjust the exposure compensation dial, you can clearly read the deviation from the base exposure in 1/3 stop increments for a maximum of ±2 stops of over or under exposure deviation. My diagrams show there is no current deviation set at this time, the compensation setting equals the meter reading.
Displaying exposure compensation this way rather then showing shutter speed number and apertures is quicker for the mind to interpret exposure adjustments and relate them to the type of scene you are shooing. So that when you are in that situation again, you can always dial in the correction, rather than repeating the same exposure error.
Soon you will be able to set corrections before you even shoot the first shot, which is vary beneficial for not wasting time on the first shot that always gets away.
Naturally you will often double check your results on the Histogram Graph and LCD monitor, but odds are, you'll be much closer to the desired exposure on the first shot and not wasting time.
Some cameras might have offered you a menu setting option where you have set your camera's exposure increment units at 1/2 stop increment adjustments, and your exposure compensation will work with these units under those settings, and your exposure compensation display will also reflect those units in some manor.
How Exposure Compensation behaves
in different exposure modes
You are allowed to make Exposure Compensation adjustments with the Aperture and Shutter Speed controls, but there are differences based on what shooting mode you currently are using.
How Exposure Mode effects adjustment options
EC adjustments in shutter speed and aperture are allowed.
AV-Mode, Canon (AP-Nikon):
EC adjustments are only performed in Shutter Speeds.
TV-Mode, Canon (TP-Nikon):
EC adjustments are only perfumed in Aperture settings.
EC adjustments are made in both Shutter Speed and Aperture but only based on your camera's criteria, you no longer make person choices about what settings your camera uses. Learn to avoid Program as a camera mode.
Pratice with Exposure
You can go outside and play with exposure readings as a kind of game, you don't have to wait the for the perfect photo opportunity to arise. I think this is the fastest way to learn the quirks of exposure, and because you are shooting digital, you can learn at a much faster rate than you would if you had to shoot film, and without all the finical burden.
Again I would steer you to the Understanding Exposure link for some helpful guidance.
As mentioned above, scenes that reflect a great deal of the light that illuminates them, like snow, or water, and even lots of the framed image being made up of sky, will tend to cause the light meter to want to turn down exposure lower than it should be. So you might want to experiment a little. Take a picture using the light meter reading, examine it and see if that scene could not benefit by being a little brighter
The situation just described is often referred to as back lighting, and subjects in the foreground often suffer by being darker than they should be.
The inverse to this scenario is also true, where the scene is dark because it manages to absorb most of the light that is illuminating it. A volcanic black sands beach would be a good example here. You could counter this scene by closing down the exposure some.
If this seems backwards to your way of thinking, then it might help to understand that the light meter is designed to read the middle gray value perfectly. Those scene that do not reflect middle neutral tones, the light meter will still set the exposure as if it were a middle tone values. Hence, we under expose for dark toned subject and over expose for light toned subjects as a compensation for the light meters readings short comings.
Shooting in Manual
Ironically the whole point of manufacturer's developing automatic shooting modes was to cut down on time consuming adjustments made for setting exposure.
But there are times when the light meter attempting to adjust for every little change in reflectivity of light is detrimental to shooting a series of pictures where your intent is to capture that action within the scene.
Shooting under a consistent light source from the same angle is one example. If you have determined the correct exposure for the scene, and this applies also when using Exposure Compensation, you don't need to keep changing exposure just because something of a little darker or lighter tones happens to be in your framed view. Light tones should be photographed light, and dark tones should photographed dark, that is of course unless you have some artistic reason to exposing otherwise. The light meter gets fooled because it is programmed to give an exposure that represents a middle value for that scene.
The Sun is a perfect consistent light source. Consider this when making exposure adjustments outdoors on a clear day when the sun is high in the sky. As the Sun gets lower, our atmosphere starts diminishing this light intensity by as much as three stops of light over an hour or so period of time.
This is a situation where shooting manual might be more practical. I use a parade shots shown below to help represent this idea.
Even though the subject matter may be constantly changing in colors and reflectivity, and brightness, there is not a lot of good reasons to keep playing with the exposure because you have already set for the light that illuminates the scene. Once you have it correct (if you have it correct), Just shoot. Subjects will reflect and be exposed relevant to their nature.
With all of these parade images below I used the same exposure on manual for controlling the highlights and background. For three of these image I also used a little electronic flash to fill in a little light to help with boosting the shadows. The basic principle here in this situation is you are shooting under a constant light source, so the light is not changing enough to worry about. Dark objects reflect low light and bright objects should be bright, so as long as you got the right base exposure, just use it.
However if you start shooting at different angles, like into the sun light, or from the other side of the street, then exposure adjustments need to be made.
If people are in the pictures, keep an eye on the flesh tones to see how they are appearing, they can serve as close middle values for exposure.
In manual mode, if you forget to adjust for your shooting situation as you change it, then you may loose a few shots until you remember your in manual mode. Semi Automatic modes are great for keeping up with exposure of different camera angles, but you still need to apply a little thought as to weather you need to also use a little Exposure Compensation on a shot per shot basis.