Exposure Compensation – Part 2 of 2
Exposure Lock
In addition to exposure compensation adjustments, we can also use our camera’s exposure lock function to create proper exposures. Unlike the exposure compensation method where we allow the camera to take a midtone reading then adjust the exposure afterwards, exposure lock allows the us, the photographer, to manually seek out an area in the scene which we consider as midtone before making an exposure.
In Canon cameras, the exposure lock button is located at the top right at the back of the camera, indicated by an asterisk *. Nikon cameras usually have an AE-L/AF-L button right next to the viewfinder (usually the same button/knob as the exposure mode selector).
Figure 1: Canon and Nikon AE-Lock
Unlike the exposure compensation method where we allow the camera to take a midtone reading then adjust the exposure afterwards, exposure lock allows the us, the photographer, to manually seek out an area in the scene which we consider as midtone before making an exposure. We’re still relying on the camera’s automatic meter to take a reading, but this time we have the option to dictate which area to meter.
It’s best to use a narrower metering pattern such as center-weighted average or even spot meter when using the AE-lock. Just keep in mind that the margin for error is higher as the pattern gets narrower.
If your camera doesn’t have a spot metering function, you can zoom in with your lens and pick a spot to AE-lock before zooming out to recompose the scene.
Take a look at Figure 2, we have a high-contrast scene where we metered the little gray device on the dash of cab. I zoomed in with my lens and pressed the AE-lock button on that area, then zoomed out to capture the scene.
Figure 2: Exposing the Bright Gray Dash
Figure 3: Histogram
We can see by the histogram that the scene is very high in contrast where the bright areas and really dark areas pretty much dominates the whole frame with minimal midtones in the photo.
Metering the device on the dashboard was a decent compromise to capture enough details in both shadows and highlight areas.
In Figure 4, I AE-locked the dark steering wheel area and told the meter to turn that to mid-tone gray. The resulting histogram shows that the area we metered is now near midtone and all the dark shadow areas in Figure 3 such as the back of the seat, the gauges in the dash, etc are now exposed better while the scene outside the car is totally overexposed.
Figure 4: Exposing for Shadows
Figure 5: Histogram
If your intended purpose is to photograph the interior of the car, then this is the exposure to make, sacrificing the highlights to expose for the shadows.
Do notice that the camera now requires a longer shutter exposure to allow more light in, resulting a to blurrier photograph.
In Figure 6, we exposed for the scene outside the car. I metered the sky and the camera turned that area near midtone. The resulting image shows tremendous amount of details in the sky and almost all the scenes outside the car but the shadows are all clipped.
Figure 6: Exposing for Highlights
Figure 7: Histogram
Since our goal was to expose the scene outside the car correctly, this is an acceptable exposure for that intended purpose.
Finally, Figure 8is an exposure I’ve chosen as the best compromise. I AE-locked on a brighter spot on the dashboard and the resulting photograph gave me ample details in both the interior and exterior of the car.
Figure 8: Balancing Highlight and Shadows
Figure 9: Histogram
Using AE-lock is a good prelude to learning how to use full manual exposure settings. AE-lock, however is faster and more intuitive when there is constantly changing lighting conditions in a scene, especially if we’re using either aperture priority or shutter priority modes in our cameras.
We can simply choose which area to meter specifically, lock the exposure and keep taking shots without changing our chosen exposure settings until the scene requires a different reading. It’s like using full manual without having the need to know exactly how much adjustments are needed in shutter speed, aperture size, and ISO setting.
Learn how to use AE-lock properly and consistently and we’ll be less reliant on unpredictable auto exposure modes and get the proper exposure we intended to capture.
