Tip of the week: Understanding camera's exposure compensation feature
One of the most common problems, especially for people who are beginners to photography is the correct camera exposure. Let us start with explaining what the term exposure means. Exposure is a combination of three camera parameters: aperture value, shutter speed and ISO value. Combining those three in proper way gets you a properly exposed image, not too bright, not too dark.
Generally, light meter built in the camera sets at least one of the three parameters, depending of the mode your camera, to achieve the properly exposed image. There are different regimes of metering light in the scene, which you can set on your camera, but we will not talk about it in this article. Lets just say that camera thinks that most of the scenes, to be properly exposed, need to be an average of middle grey tone (18% grey). So if the average is darker than middle grey, camera will adjust the exposure to higher values and vice versa. Problem arises when the proper exposure of the scene is not an average of a middle gray. Then, the camera is not exposing the scene properly. This can happen if there is a lot of contrast in the scene (sunsets), or if there is too much white areas (snowy scenes) or dark areas. In those cases, camera’s exposure compensation feature comes very handy.
Camera exposure compensation feature is not always located in the same place. Depending on the camera type or brand it can be found in different places. Sometimes it is inside the menu which is the most inconvenient place. On most dSLR cameras it is a dedicated button which you need to hold and rotate the aperture dial simultaneously to change the exposure compensation. On most mirrorless cameras and some dSLR cameras there is a dedicated dial for this feature which is, in my opinion, the most convenient option.
This is how the exposure compensation dial looks:
On the screen it looks like a bar going to the left or to the right of the middle zero “0” value.
And this is how it looks as a dedicated button:
Let’s see how changing the exposure compensation reflects on aperture, shutter speed, or ISO values. If you take your image and you see that it is too dark or too bright, you can quickly change the exposure compensation to adjust the image brightness so the image looks properly exposed, or exposed in the way you like it. If your image is too dark, you need to dial the exposure compensation to positive (+) values. If it is too bright you need to go to negative (-) values. I will not say to the left or to the right because in some cameras you can set if the positive values are to the left or to the right of the middle „0" value.
If you correct the exposure compensation the camera changes either aperture, shutter speed or ISO depending of the mode set in the camera:
Manual exposure mode
If you are in manual exposure mode, changing the exposure compensation does nothing. Except if your ISO is set to AUTO. If it is, then it corrects the ISO value to lower or higher values depending you want the image brighter or darker. I do not recommend setting the ISO to AUTO for photography since high ISO values can dramatically degrade the quality of your photo.
Aperture priority mode
Since the aperture priority mode allows you to change only the aperture so that the camera adjusts the shutter speed to properly expose the image, using the exposure compensation changes the shutter speed to longer or shorter values, keeping your aperture fixed to the value you have set. It is good to mention that if the exposure compensation feature sets the shutter speed to very long values, your image can get blurry if not using a tripod.
Shutter speed mode
Contrary to the Aperture priority, in this mode, the exposure compensation works the other way. You are setting the fixed shutter speed and the camera sets the aperture. Thus changing the exposure compensation makes the camera change the aperture. Be aware that in this case camera is limited to the lens widest aperture, so if the exposure is already using the widest aperture, you cannot make the image brighter using exposure compensation since the aperture cannot go wider because of the limit of the lens.
Exposure compensation is a very useful and convenient feature. You can quickly adjust the brightness to your liking. Even if the camera light meter did set the proper exposure, sometimes you want the image to be darker or lighter, depending of the mood of your image. Try and experiment with it, you will be surprised how easy and quickly you can change the lightning of your scene, to your liking.
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