Understanding Aperture Priority Mode in Photography

One of the most useful camera modes is called aperture priority . To use this mode, all you need to do on most cameras is spin your camera’s PASM dial to the “A” or “Av” setting.

What Is Aperture Priority?

Aperture priority is a camera mode in which you manually set your aperture, while the camera automatically selects a shutter speed.

That’s all there is to it. So, what makes aperture priority mode so valuable?

First, it gives you full control over the single most important setting in all of photography – aperture. (Manual mode is the only other way to get full control over aperture.) Get aperture right, and everything else follows.

Second, aperture priority mode is fast to use. That’s especially true compared to manual mode, which takes more time to set properly when the light is changing.

In short, if used right, aperture priority mode lets you pick the optimal camera settings – just like in manual mode – but more quickly.

How to Use Aperture Priority Mode Optimally

Aperture priority is not hard to use, so long as you understand aperture, ISO, and shutter speed.

First, enter aperture priority mode by turning your PASM dial to “A” (or “Av” on Canon cameras). With some Fuji and Leica cameras, you get the same effect by turning the Shutter Speed dial to Auto.

Second, you must select your aperture manually – the f -stop you plan to use. In aperture priority mode, the camera will never change the aperture you select. So, it’s very important to pick the right one for your desired depth of field (and other factors).

Third, select the proper exposure compensation. Be sure not to overexpose any important highlights in your image. Often, this will necessitate -0.3 or -0.7 exposure compensation. (This setting works by altering which shutter speed your camera selects, shifting the exposure in your desired direction.)

Fourth, pick the right ISO. If your subject isn’t moving, and you’re shooting from a tripod, stick to base ISO. This is ISO 100 on most cameras.

I’ll cover handheld photography in a moment, but hopefully you can see why aperture priority mode is so quick to use. For something like landscape photography, you can pick a good aperture (maybe f/8), a reasonable exposure compensation (say, -0.3 EC), and base ISO – and then you’re done.

No matter how the light changes, your camera is now, essentially, set-it-and-forget-it. Yet your settings are optimal.

Shooting Handheld

For tripod-based photography, aperture priority mode is clearly useful and easy to set. But when you’re shooting handheld or your subject is moving quickly, things are a bit different.

As you know, aperture priority mode requires your camera to select a shutter speed automatically. But in dark conditions, it’s going to select a long shutter speed – say, 2 seconds – which you won’t be able to handhold sharply.

The solution is to increase ISO. As you leave base ISO and jump to ISO 400, 800, 1600, and so on, your camera will use a faster shutter speed to compensate. And you’ll get back into handholding territory.

Although you can increase ISO manually, a quicker way is often to use Auto ISO.

Auto ISO

The genius of Auto ISO is that it has a built-in shutter speed limiter. Rather than worrying about your camera selecting a 2-second shutter speed in aperture priority mode, you can manually limit shutter speed to a safer value. Maybe 1/100 second for regular handholding, or 1/500 if you’re photographing sports.

In fact, you can even limit shutter speed to change as you zoom in and out. (That’s found by changing “Minimum Shutter Speed” to “Auto.”)

By default on most cameras, this lines up with the “1/focal length” rule. With a 24-120mm zoom, the camera would stick to 1/25 second or faster at the wide end, and 1/125 second or faster at the telephoto end. (Many cameras today let you adjust this default behavior to be faster – i.e., 1/50 and 1/250 instead – or slower, if you so choose.)

My final recommendation:

  • If you’re shooting handheld, use aperture priority mode with Auto ISO and Auto Minimum Shutter Speed. If you want to be safe, prioritize Auto Minimum Shutter Speed one click “faster” than default.
  • If you’re shooting sports, use aperture priority mode with Auto ISO. Use a manual minimum shutter speed of 1/500, 1/1000, or whatever you feel will comfortably eliminate motion blur.

This is only a brief explanation of how useful Auto ISO can be. If you want a good primer on Auto ISO, take a look at our complete guide on the subject.

When to Avoid “A” Mode

I use aperture priority about 95% of the time for my own photography – regardless of the genre I’m shooting and whether I’m using a tripod. It’s just that flexible.

But sometimes, aperture priority mode is not ideal. That’s especially true when you need to use the same camera settings across a series of photos. For example, with panoramas or focus stacking, I almost always use Manual mode.

The same is true in conditions when automatic exposure gives you poor results. For example, with Milky Way photography, cameras rarely meter your scene correctly. Even with exposure compensation, you will often get images that are too dark or inconsistently exposed in aperture priority mode. I always use Manual for taking star photos, or other images in very dark conditions.

Aperture priority mode also restricts you to shutter speeds of 30 seconds (on most cameras) or shorter. If you want to use your camera’s bulb or time mode, you will need to be in Manual.

On top of that, I recommend using manual mode if you do flash photography. Otherwise, you won’t have total control over the balance between flash and ambient light. All of my flash-lit macro photography is done in manual mode, for example.

Lastly, some photographers like using manual mode in combination with Auto ISO for shooting sports and wildlife. That’s not a bad method in low light, but in bright conditions, you’ll be in danger of overexposure (because the camera will hit base ISO and not be able to go any darker). With aperture priority mode, you have all the same benefits without the overexposure problem, since the camera simply uses faster shutter speeds once it hits base ISO.

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