Exposure Modes, Metering Modes & Exposure Compensation
By Marc F Alter
In many ways our digital camera are like mini-computers; helping us achieve balanced compositions, focus and exposures. For Exposures, there are several different types of settings we can use that tell our camera how we want it to act. One of these is known as Exposure Modes. Typical DSLR (Digital Single Lens Reflex) Exposure Modes are Auto, P, A, S and M:
- Auto (Automatic Exposure) – Automatic Exposure is a feature on many DSLRs that allows the photographer to simply point and shoot to get a fairly good exposed image (in some cases) based on the amount of light in the scene. With this mode, the camera automatically adjusts the ISO, Aperture and Shutter Speed to what it believes is the correct setting. This setting is usually in Green and is not available on some of the more advanced DSLRs. This is because setting your camera on Auto often also locks you out of other DSLR settings like Metering Modes, White Balance, Focus Modes, Exposure Compensation, etc.
- P (Program) – Also joking known as “Professional”, this Exposure Mode is similar to automatic in that the DSLR attempts to automatically adjust the Shutter Speed and Aperture for optimal exposure. Although some “P” mode adjustments may vary from one camera manufacturer or model to another, when you point your DSLR to a bright scene, the Aperture automatically adjusts to a higher F-Stop while setting the Shutter Speed reasonably high (to let in less light). When you point your DSLR to a dark scene, the Aperture automatically adjusts to a lower F-Stop while setting the Shutter Speed low (to let in more light).
The difference between Auto and Program Mode is with “P”, the photographer has the ability of adjusting the camera selected settings. You have the option of setting the ISO, Aperture, Shutter Speed and many of the other camera settings (ie; Metering Modes, White Balance, Focus Modes, Exposure Compensation, etc). Typically, if you change Aperture, the camera will automatically change the Shutter Speed. If you change the Shutter Speed, the camera will automatically change the Aperture. If you change both the Shutter Speed and the Aperture, the camera will change the ISO (light sensitivity setting).
- A or Av (Aperture Priority) – With this Exposure Mode, the photographer determines and sets the Aperture size. Once this is done, the camera measures the amount of light at the scene and then automatically adjusts the Shutter Speed. This has the advantage of the photographer selecting the DOF (Depth of Field) needed for the composition. At a given F-Stop, if the scene is bright, the camera will automatically adjust the Shutter Speed to be faster (to reduce the amount of light coming into the camera). If the scene is dark, the camera will automatically adjust the Shutter Speed to be slower (to increase the amount of light coming into the camera). With this mode, the camera does not adjust the ISO.
- S or Tv (Shutter Priority) – With this Exposure Mode, the photographer determines and sets the Shutter Speed. Once this is done, the camera measures the amount of light at the scene and then automatically adjusts the Aperture. This has the advantage of the photographer selecting the amount if time of shutter is open for the composition. At a given Shutter Speed, if the scene is bright, the camera will automatically adjust the Aperture to be higher (to reduce the amount of light coming into the camera). If the scene is dark, the camera will automatically adjust the Aperture to be lower (to increase the amount of light coming into the camera). With this mode, the camera does not adjust the ISO.
- M (Manual) – This setting basically tells the camera to not make any automatic adjustments. It is up to the photographer to manually set the ISO, Aperture and Shutter Speed.
Metering Modes – In addition to Exposure Modes, many DSLRs also offer a setting that allows you to control how much of the scene the camera considers when calculating a “correct exposure”. Different Metering Modes typically include “Metrix, Center, Spot” (although some more advanced DSLRs may have additional settings as well).
- Matrix/Evaluative/Full – This setting typically sets the camera to use the entire frame when calculating a correct exposure. Depending on the camera, “Matrix Metering” may use the center areas more than the corners when determining correct exposures. Some cameras also offer Group Metrix Metering, allowing the photographer to select how large an area to use and where that area is located within the frame. This type of metering works well in scenes that are evenly lite.
- Center Priority / Center Weight – This setting sets the camera to use only the middle of the frame when calculating a correct exposure. This type of metering works well in scenes where the subject is in the center of the frame and you care less about how the outside areas are exposed.
- Spot - This setting sets the camera to use a single area in the frame when calculating a correct exposure. This point is typically only about 5% of the frame and its location can be chosen by the photographer using the Focus Point(s). This type of metering works well in scenes that are unevenly lite and where the subject may be off center.
Exposure Compensation – Things never always go as planned and sometimes this is true for exposures. After taking care to select the right Exposure Mode and Metering Mode for your subject, you take a test shot and check the Image’s Blinkees and/or Histogram; you spot a problem. Either the Blinkees are flashing (indicating you are blowing out some white areas) and/or the Histogram shows its right up against the extreme right (too bright) or extreme left (too dark). What is a person (photographer) to do? This is where Exposure Compensation comes into use.
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Under-Expose Image Over-Expose Image
- Exposure Compensation allows the photographer to intentionally adjust the automatically calculated exposure values when using P (Program), A (Aperture Priority), or S (Shutter Priority). Typically when using the Exposure Compensation function your camera, you view a scale with a Zero in the middle. As you adjust the Compensation to the right, you are telling the camera to Over-Expose from its automatic calculated exposure vales. As you adjust the Compensation to the left, you are telling the camera to Under-Expose from its automatic calculated exposure vales. You can usually move this setting in either 1/2 or 1/3 increments.
When else might you use Exposure Compensation? Maybe when you are shooting in conditions (ie; snow, fog, etc), where the camera is attempting to turn the scene grey instead of recording white. Or when your Subject is surrounded with lots of bright backlite light, resulting in your subject becoming underexposed. Each picture you take may be different and you need to learn how to adapt to capture the best image you can.