Aperture Priority–The Auto Exposure For Photographers

Text and Photography by Chuck Place

I almost always have my camera set to “Manual” exposure. I admit it. I’m a “Manual” snob. Taking full control of my camera’s shutter speed and aperture, or f-stop, gives me perfect exposures no matter the subject or the lighting.

Making the leap from “Program”, where the camera makes all the exposure decisions, to full “Manual”, where the photographer is in charge, is a big step however. Let’s face it, “M”, or “Manual”, can be rather intimidating.

Are all the auto-exposure settings a waste of time? No, of course not, but one is better than the others.

Back lighting for Aperture Priority exposure of sailboarding

Back lighting of sailboarder in Aperture Priority exposure can be tricky.

Let’s break down exposure. Assuming a proper exposure is the final result, shutter speed usually just needs to be fast enough to produce a sharp subject. Whether 1/500, 1/1000 or 1/2000—they all will look the same, assuming you aren’t photographing a hummingbird. Shutter speed is generally used to freeze motion—and give you a proper exposure, of course.

Set Aperture Priority exposure for great depth of field in landscapes

Set Aperture Priority exposure for great depth of field in landscapes

Aperture settings, or the f-stop, also control exposure, but determine depth of field in an image as well. Depth of field, or how much of the image in front of and behind the plane of focus is sharp, is one of the most powerful tools in photography. Changing from great depth of field to very shallow depth of field completely changes how a viewer “reads” your photograph. The storyline of an image changes dramatically with a change in depth of field.

Aperture Priority works well for dusk images

Aperture Priority works well for dusk images but a tripod may be necessary for the long exposures.

Aperture, or f-stop, is the exposure setting that a photographer must control absolutely!

Conveniently, there is an auto-exposure setting on most cameras that allows a photographer to set the proper depth of field while the camera picks the appropriate shutter speed for a correct exposure—“A” or “Aperture Priority”.

Photographing people often requires shallow depth of field to separate the subject from the background.

Photographing people often requires shallow depth of field to separate the subject from the background.

If you want to separate your subject from the background of an image, set your aperture, or f-stop, to a wide opening of f2.8 to f5.6 for a shallow depth of field. Conversely, if the background or environment is as important as the subject, pick an f-stop that creates greater depth of field, say f16 or f22. The photographer must make the decision on how much depth of field is appropriate, then the camera picks the shutter speed to create a proper exposure.

Aperture Priority for travel subjects

The Aperture Priority exposure setting is perfect for travel photography under changing light.

“Aperture Priority” is especially useful in situations where the lighting changes quickly, like sports, weddings, travel, concerts and street photography. It’s fast and eliminates half the work of “Manual” exposure.

Is it foolproof? Well, no.

Pick shallow depth of field for food shots using Aperture Priority exposure settings

Pick shallow depth of field for food shots using Aperture Priority exposure settings

Your camera may still underexpose sunsets like the one above, light-colored buildings and backlit subjects just like it did on “P”. Much of the time, however, the exposures will be great and each image will have the depth of field that you want, rather than what the camera “thinks” is correct.

Even in the tricky lighting environments listed above, the exposure will be close and can be corrected in post-production. Not that I advocate fixing everything in post—quite the opposite—but the “A” exposure setting makes setting exposure relatively fast and painless. Take control but make it easy. Shoot in Aperture Priority and relax!