How to Use Exposure Lock in Critical Image Areas: Selective Metering Controls Automatic Exposure In Digital Cameras

There are several ways to deal with difficult exposure and get the correct exposure setting for a portion of a view. All have their advantages and some depend upon the style and personal preference of individual photographers.

Strong colors and large bright or dark areas in the background distract the digital camera’s inbuilt light meter seeking to find a compromise setting for the whole scene.

How

Move in close to the subject, or zoom in, so it fills the viewfinder and then activate the camera’s inbuilt light meter, usually by half depressing the shutter release button. Then press the conveniently located aperture lock button to freeze the current exposure settings in the camera. Then compose the picture and shoot using the locked exposure settings. The buttons are usually labelled as AE-L or with a key symbol.

Alternative Methods

One option is manual metering, using the same basic metering technique. Rather than locking an automatic setting, the shutter speed and aperture are set and stay that way until the photographer changes them. This is a good method when there are a number of shots required and the subject is unlikely to move, and the light will remain reasonable constant, such as still life or some landscape settings.

Then there is exposure compensation for automatic metering modes. Although this still is all about the overall scene, and not about finding an accurate exposure setting for particular area of the scene.

Using the spot metering mode is another technique, although sometimes it may not be convenient or fast enough. On some DSLRs, mode selection is via menu options, so it is faster to use the aperture lock on a normal automatic metering method.

Advantages of Exposure Lock

The key advantage of the exposure lock method is that it delivers accurate exposure of a critical area of the scene quickly. Depending upon the camera, it allows the use of automatic exposure modes to determine the exposure of an area and then apply this to the image overall. In the example photo of the white fishing boat at the docks the very bright white hull, which is the central feature of the image,

For occasions such as weddings where the subject may be difficult to arrange and get impatient while posing speed is important. This results in wooden looking people unhappy about waiting around while the photographer tries to correct the exposure.

Camera Differences

Although this is a common feature in DSLRs, there are some detail differences in the implementation between cameras. For example, in the Pentax DSLRs the exposure stays locked while the meter stays on. This is set in a custom menu at 3, 10 or 30 seconds.

On the other hand, there are a number of different exposure lock modes in Nikon’s D90 DSLR. It will stay locked while the button is pressed, or until the photographer presses the button again. There is also the mode where it stays locked only while the meter operates, as with the Pentax system. This is set in a custom menu.