In previous blog posts (here and here), I've written about how using the Exposure Compensation control on your digital camera can produce more pleasing exposures, especially of all white or all black subjects. However, depending on which exposure mode you are using, you might not get the effect you were expecting, even when you set the Exposure Compensation correctly. Let's take each exposure mode in turn and see what happens when you adjust the Exposure Compensation control.
In Program exposure mode (P), you select the ISO and the camera adjusts the shutter speed and aperture settings for an average brightness picture. When you dial in a change with Exposure Compensation, the camera can modify either the shutter speed, the aperture or a combination of both to produce a brighter or darker picture. So you get the brighter or darker photo you want.
In the examples above, the camera changed both the shutter speed and the aperture to make a +1 brighter exposure.
In Aperture Priority exposure mode (A or Av), you select the ISO and the aperture while the camera changes the shutter speed for an average brightness image. When you change the Exposure Compensation control in this situation, the camera adjusts the shutter speed to a longer or shorter time for a brighter or darker photo, respectively. Most digital cameras have lots of shutter speeds to work with, from 30 seconds to 1/4000 second on most advanced models. So it's easy for the camera to make a brighter or darker photo with Exposure Compensation.
In the preceding two photos of part of a steam engine, the camera adjusted the shutter speed to make a -2 darker exposure.
In Shutter Priority exposure mode (S or Tv), you choose the ISO and the shutter speed while the camera adjusts the aperture for an average brightness picture. When you dial in some Exposure Compensation, the camera changes the aperture to be larger or smaller for a brighter or darker image, respectively. However, most lenses have a limited range of apertures for the camera to pick from, usually f/4 to f/22 on a standard zoom lens. That is only five full stops of light compared to 17 full stops with shutter speeds. This means that the camera is more likely to run out of useable apertures to make the picture lighter or darker when you change the Exposure Compensation. So you can change the Exposure Compensation setting, but the camera might not make any adjustment to the image brightness because it has run out of aperture options.
In the two images above, the lens only opens to f/4. Because the lens was near its maximum aperture (1/3 stop away), the camera could not open the lens wide enough to make the picture noticeably brighter. In order to achieve a +1 exposure compensation, I manually adjusted the ISO to 200, making the sensor see more of the light. The shutter speed and aperture remained the same.
In Manual exposure mode (M), you are making all the choices for ISO, shutter speed and aperture, so you can dial in the necessary adjustments for a lighter or darker photo without needing to use the Exposure Compensation button.
In these flower photos, I manually changed the shutter speed to a faster 1/400 second to produce the equivalent of a -1 change in exposure, without using the Exposure Compensation control.
Bottom line: be aware that Exposure Compensation is more limited when you work in Shutter Priority exposure mode. Sometimes it will work as you expect; other times the camera may run out of apertures to give you the brighter or darker image you want. In that case, consider changing the ISO setting or switching to a different exposure mode to get the exposure you want.
Learn about more things you can do to make better pictures in Getting to Know Your Digital SLR Camera on Saturday, May 18, 2019, in Missoula, Montana. Click here to register.
In Program exposure mode (P), you select the ISO and the camera adjusts the shutter speed and aperture settings for an average brightness picture. When you dial in a change with Exposure Compensation, the camera can modify either the shutter speed, the aperture or a combination of both to produce a brighter or darker picture. So you get the brighter or darker photo you want.
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| Program Exposure Mode 1/250 second, f/8, ISO 200 Exposure Compensation 0 |
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| Program Exposure Mode 1/160 second, f/7.1, ISO 200 Exposure Compensation +1 |
In the examples above, the camera changed both the shutter speed and the aperture to make a +1 brighter exposure.
In Aperture Priority exposure mode (A or Av), you select the ISO and the aperture while the camera changes the shutter speed for an average brightness image. When you change the Exposure Compensation control in this situation, the camera adjusts the shutter speed to a longer or shorter time for a brighter or darker photo, respectively. Most digital cameras have lots of shutter speeds to work with, from 30 seconds to 1/4000 second on most advanced models. So it's easy for the camera to make a brighter or darker photo with Exposure Compensation.
 |
| Aperture Priority Exposure Mode 1/60 second, f/8, ISO 100 Exposure Compensation 0 |
 | |
| Aperture Priority Exposure Mode 1/250 second, f/8, ISO 100 Exposure Compensation -2 |
In the preceding two photos of part of a steam engine, the camera adjusted the shutter speed to make a -2 darker exposure.
In Shutter Priority exposure mode (S or Tv), you choose the ISO and the shutter speed while the camera adjusts the aperture for an average brightness picture. When you dial in some Exposure Compensation, the camera changes the aperture to be larger or smaller for a brighter or darker image, respectively. However, most lenses have a limited range of apertures for the camera to pick from, usually f/4 to f/22 on a standard zoom lens. That is only five full stops of light compared to 17 full stops with shutter speeds. This means that the camera is more likely to run out of useable apertures to make the picture lighter or darker when you change the Exposure Compensation. So you can change the Exposure Compensation setting, but the camera might not make any adjustment to the image brightness because it has run out of aperture options.
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| Shutter Priority Exposure Mode 1/500 second, f/4.5, ISO 100 Exposure Compensation 0 |
 |
| Shutter Priority Exposure Mode 1/500 second, f/4.5, ISO 200 Exposure Compensation +1 |
In the two images above, the lens only opens to f/4. Because the lens was near its maximum aperture (1/3 stop away), the camera could not open the lens wide enough to make the picture noticeably brighter. In order to achieve a +1 exposure compensation, I manually adjusted the ISO to 200, making the sensor see more of the light. The shutter speed and aperture remained the same.
In Manual exposure mode (M), you are making all the choices for ISO, shutter speed and aperture, so you can dial in the necessary adjustments for a lighter or darker photo without needing to use the Exposure Compensation button.
 |
| Manual Exposure Mode 1/200 second, f/4, ISO 400 Exposure Compensation 0 |
 |
| Manual Exposure Mode 1/400 second, f/4, ISO 400 Exposure Compensation 0 |
In these flower photos, I manually changed the shutter speed to a faster 1/400 second to produce the equivalent of a -1 change in exposure, without using the Exposure Compensation control.
Bottom line: be aware that Exposure Compensation is more limited when you work in Shutter Priority exposure mode. Sometimes it will work as you expect; other times the camera may run out of apertures to give you the brighter or darker image you want. In that case, consider changing the ISO setting or switching to a different exposure mode to get the exposure you want.
Learn about more things you can do to make better pictures in Getting to Know Your Digital SLR Camera on Saturday, May 18, 2019, in Missoula, Montana. Click here to register.