There may be 50 shades of grey, but when we are talking about exposure the only one we’re concerned about is 18% grey. I would like to talk a little about how we can keep control of exposure when we are not in manual mode.
You may be ringt, but you may not be correct:
Exposure compensation is used to override the suggested correct exposure as calculated by your camera’s light meter. It is important to understand how your camera is determining what is the correct exposure. The meter in the camera is measuring the light in the scene and tries to balance the overall scene to a middle gray tone, also known as 18% grey.. If the main subject of your image is of a tone that is lighter or darker then 18% grey the calculated exposure will be under or over exposed. This is where exposure compensation comes in to save the day.
In order to use exposure compensation, you must be in one of the camera modes that allows the camera’s meter to make exposure decisions. This would include aperture priority, shutter priority, or the program mode. If you are in manual mode, exposure compensation will do nothing unless you have Auto ISO enabled. Basically, exposure compensation is only usable if the camera is incharge of making the exposure decision. Once the proper camera mode is selected, it will be possible to override the exposure calculated by your camera by using the exposure compensation.
Clear as mud:
So what does exposure compensation actually do? You know that it changes the exposure, but how does it do it? Does it change the aperture, shutter speed, or is it pure magic?
The answer is that it depends on what mode you have your camera in, and which camera you have. In general exposure compensation in various modes works like this…
Aperture Priority Mode – In Aperture Priority mode, exposure compensation changes the shutter speed. In this mode, you set the aperture and the camera sets a corresponding shutter speed. If you change the Aperture, your camera just sets another corresponding shutter speed, and there is no change in the exposure level. Exposure compensation gives you the ability to change the shutter speed (and the overall exposure value) while staying at the same aperture you originally set.
Shutter Priority – In Shutter Priority mode, exposure compensation changes your aperture. It is basically the reverse of Aperture Priority mode. You set a shutter speed, and the camera sets a corresponding aperture. Exposure compensation therefore changes the exposure by allowing you to change that aperture size.
Program – In Program mode, or P on your mode dial (no P does not stand for Professional”, exposure compensation usually changes the shutter speed. It is possible that your camera works differently, or that you can change how it works in the camera’s menu. This is a good excuse to read some of your camera’s instruction manual.
Let’s talk about when you might want to use exposure compensation. You may wonder why you’d want to change anything, if your camera is already determining the proper exposure level.
if the tones in your frame are darker than this 18% grey tone, the meter will show that there is not enough light for a proper exposure so it will overexpose the image causing the darker tones to become grey. Conversely, if the tones in your frame are lighter than middle grey it will underexpose the image causing whites to become grey.
SInce I live in a town with the nickname of Winterpeg, here is an example that I encounter for almost 1/2 the year. Taking pictures of a snowy scene. If I was to just trust the camera to calculate the exposure all that “wonderful” snow would come out looking grey. I need to add positive exposure compensation of up to 2 stops if I want the snow to be white.
How much is the doggy in the window:
Another common situation where you would want to use exposure compensation is when your subject is strongly backlit, and you do not want a silhouette. This will often happen when you have a subject standing in front of a window. This can really fool a camera meter. With all the light coming from behind the subject you may need to add 2 or more stops of compensation to get a good exposure of the subject.
Not all positive:
I have given a couple of examples of when positive exposure compensation would be needed, but when would you need to add negative compensation? Remember that the camera is trying to make everything 18% grey, so if your subject is darker then that you will need to add negative compensation. Let’s consider the following situation; you are taking a landscape image of a spectacular prairie sunset over a hay bale field. the sky is 2/3rd’s of your scene, but the bottom 1/3rd is the field. this dark field at the bottom will in most situations probably cause your camera to overexpose the scene as it tries to balance the different tonal ranges and bring some detail into the foreground. In this case let’s also assume that the focus is the sky not the field. You would have to dial in negative exposure compensation to preserve the colours and detail in the sky.
A Photographer should have complete control over the exposure process, but not all of us want to work in manual mode. Working in aperture or shutter priority can allow you to work faster, but by adding exposure compensation to your process, you can get the speed of other modes, along with the control of manual.
If you haven’t used exposure compensation before, give it a try.
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There will not be a blog next week as I will be away from the computer.
Thanks again for taking the time to read my blog. Please click the like button if you like it, and as always please leave any questions in the comments and I will answer them.