Exposure compensation allows you to increase or decrease the standard exposure set by the camera. It’s particularly useful when photographing overly bright or dark subjects, high-contrast scenes, or in situations with considerable backlighting, all of which may deceive the camera’s auto-exposure programming to set exposure values that misrepresent what you saw. White sand beaches and snowscapes present familiar scenes in which cameras can set erroneous exposure values. Since these scenes feature high-reflectance surfaces spread evenly across the frame of your composition, and because the camera’s reflected-light meter sets exposure values to render subjects as middle grey, the resulting pictures are typically underexposed. Exposure compensation is the fix: it lets you use your better judgement and understanding of the subject to override the camera’s auto-exposure programming in situations where mistakes are likely.
On most cameras, exposure compensation is activated by a dedicated button marked by a square icon featuring a black on white + (plus) and a white on black – (minus). Pressing the button and rotating the appropriate dial will input the desired level of exposure compensation. (The exact procedure is camera-specific, so check the user’s guide.) The amount of exposure compensation you set is shown by the position of the exposure level indicator or by a number, both representing units of EV. In general, exposure compensation may be set in increments of ⅓ EV, up to a total deviation of ±2 to ±5 EV (depending on camera model).
Regardless of your selected auto-exposure or metering mode, by setting exposure compensation to +1 EV, you’re instructing the camera that it must increase its auto-exposure value by one stop (i.e., one-stop overexposure compared to the camera’s standard). The process works in the opposite direction, too; by setting exposure compensation to –2 EV, you’re instructing the camera to reduce its automatically determined exposure by two stops (i.e., 2-stop underexposure compared to the camera’s ideal).
The parameters adjusted by exposure compensation correspond to your selected auto-exposure mode. On most cameras, exposure compensation is only available in the Program, Shutter Priority, and Aperture Priority auto-exposure modes. In Program mode, exposure compensation is achieved by adjustments to both the shutter speed and aperture. In Shutter Priority mode, exposure compensation is performed by changes to the aperture. The camera will warn you when your desired level of compensation requires an aperture value beyond what the lens can achieve. In Aperture Priority mode, exposure compensation is made by adjustments to the shutter speed. The camera should warn you when your desired level of negative compensation requires a shutter speed that is faster than your camera’s capability. Exposure Compensation isn’t available in Manual mode because the shutter speed, aperture, and ISO are determined by the user, and there’s no auto-exposure program to override.
Exposure compensation and metering modes
Exposure compensation requires the ability to anticipate when a camera’s auto-exposure program may lead exposures astray, and your choice of metering mode can either assist or hinder this effort. In general, there’s greater uncertainty in predicting the degree of exposure compensation a scene requires when your camera’s metering mode is set to something sophisticated, such as evaluative, matrix, or multi-pattern metering because it’s hard to determine to which parts of a scene the camera will assign greater prominence. The amount of exposure compensation a subject requires is more predictable when the camera’s meter is set to average and centre-weighted metering. In either of these modes, you can perform a quick mental analysis of the tonal variations in the scene, and either defocus your eyes or squint them to get a sense of the averages your camera will prefer and then make the necessary adjustments using your better judgment.
Lastly, spot metering provides the most accurate method of setting exposure compensation because it allows you to isolate a single tone within the composition precisely and fix compensation according to whether you believe that tone should be exposed brighter or darker than middle grey, and by how much (if at all).
Exposure compensation and skin tones
The accurate representation of skin tone and colour has been the pursuit of photography for many decades, with most (relatively) modern consumer and professional films being specially formulated to provide both accurate and pleasing results. Portraits require particular attention because people are acutely sensitive to noticing slight deviations from a precise representation of skin tone and colour. If the intention of your photography is portraits of people featured prominently in the frame, then you should consider taking a spot meter reading off the subject’s face to determine what degree of exposure compensation suits them. Auto-exposure bracketing could be useful in such circumstances. In general, individuals with light and pale skin tones render well with +1/2 to +2/3 EV compensation, and individuals with dark to very dark skin tones present nicely with 0 to –2/3 EV compensation.
Exposure compensation and auto-exposure lock
There will be circumstances in which you’re tasked with taking pictures of multiple subjects under the same lighting. However, if the scene contains a variety of unevenly dispersed tones, either on your subjects or their surroundings, the camera’s auto-exposure programming may set wildly different exposures values between each picture, despite the consistency of the incident light. Although correctly setting exposure compensation for each photo can accomplish consistent and accurate results, the amount of compensation will change between images, and making these decisions will become tedious. Fortunately, there’s a more efficient way to handle such situations.
Auto-exposure lock, or AE lock, is a feature common to many DSLRs and mirrorless cameras and allows users to lock the camera’s auto-exposure values temporarily. AE lock is useful in situations where you plan on taking pictures of varied compositions or subjects under the same lighting conditions, and in cases where the area of focus is different from the exposure metering zone. For a detailed overview of your camera’s implementation of AE lock, refer to its user’s guide. In general, the AE lock functions in one of two ways on most cameras, either as a press and hold button or as a switch. Pressing and holding the AE lock button locks the exposure to the currently displayed values for the duration the button is pressed. When used as a switch, the exposure is locked when the AE lock button is pressed and released when the button is pressed again (or after the camera is powered off and on). When AE lock is used in conjunction with exposure compensation, the camera’s standard auto-exposure value is locked, but you may still vary the total exposure by adjusting exposure compensation.