Read any good photography tutorial—including all the ones on this site—and you’ll see one bit of advice repeated over and over again: shoot using Aperture Priority mode. So, why do so many professional photographers love Aperture Priority? What makes it so good? Let’s find out.
Aperture Priority mode (Av or A on the mode dial) is one of the two semi-automatic modes your camera has. The other is Shutter Speed Priority (Tv or S on the mode dial). In Aperture Priority mode, you set the aperture and ISO while your camera automatically sets the shutter speed based on its light meter reading. In Shutter Speed Priority mode, you set the shutter speed and ISO, your camera sets the aperture.
With Aperture Priority mode, you don’t give up control over how your images look. If your camera is picking a shutter speed that overexposes or underexposes the scene, you use exposure compensation to adjust it without having to worry about selecting an exact shutter speed.
Now, let’s look at why it’s great.
Aperture Controls How Things Look
Aperture is one of the most important factors in how things appear in your images since it’s what controls the depth of field. If you use a wide aperture, like f/1.8, you’ll have a narrow depth of field with only a small area of the image in focus and a nice blurry background.
On the other hand, if you use a narrow aperture like f/16, you’ll have a really wide depth of field with almost everything sharp.
I shot both the images above with the same 85mm lens, but they’re drastically different, in part due to the aperture. I just couldn’t have shot the portrait well at f/16 or the skyline at f/1.8.
Whatever lens you’re using, the aperture you use is going to be a big part of how the final photo looks. Shutter speed—which we’ll look at next—matters, of course, but not as much as the aperture in most situations.
Shutter Speed Is Less Sensitive to Change (At Handheld Speeds)
Shutter speed falls into two broad categories: fast enough to use your camera handheld or slow enough to blur motion. The general rule is that if you’re not using image stabilization, the slowest shutter speed you can reliably use is 1/[the focal length of the lens, accounting for crop factor] of a second. In other words, if you’re using a 100mm lens, your slowest handheld shutter speed is 1/100th of a second; if you’re using a 50mm lens, it’s 1/50th of a second.
Unless you’re shooting really fast moving subjects, the difference between 1/100th of a second and 1/4000th of a second just doesn’t matter too much to the overall look of things. That’s a 6-stop difference; the aperture equivalent is going from f/1.8 to f/14. The photo above was shot at 1/125th of a second; the one below was shot at 1/1600th of a second; can you spot the difference?
This is why Aperture Priority mode is so much more useful than Shutter Speed Priority mode. For shutter speed to really affect how your image looks, you need to slow down and use a tripod, in which case, you’re probably going to use Manual mode. To take both photos above, I just put my camera in Aperture Priority mode at f/1.8; the camera chose an appropriate shutter speed. As long as it doesn’t drop too low—in which case increase your ISO—you’re going to come away with good shots reliably.
It Keeps You Flexible
Manual mode is great for consistency. You can dial in your settings and know that each photo is going to be identically exposed—assuming nothing changes in the scene. It is, however, inherently inflexible. If something changes, you have to adjust everything.
Aperture Priority mode, on the other hand, is incredibly flexible. You can go from shooting a close up portrait at f/1.8 to shooting a group shot at f/8 with a single dial twist. If you’re doing street photography, you can go from dark alleys to bright plazas and not have to change a thing. If your shutter speed ever drops too low, all you have to do is increase your ISO—something that takes seconds—to keep the quality of your shots high. Similarly, if your camera starts underexposing or overexposing, you can tweak the exposure compensation and keep going.
When we advocate manually controlling your camera here on How-To Geek, using Aperture Priority mode like this is what we’re talking about. You don’t have to enter every single setting by hand, but you should understand what your camera is doing at any given time, and have things set up in such a way that you control how the final image looks. If shutter speed doesn’t matter, then let your camera pick it. And when it’s picking the wrong one, all you have to do is adjust the ISO or exposure compensation.