Understanding aperture priority (and exposure compensation) to improve your photography

Up until 2018 or so, I was an avid proponent of only photographing in full manual mode, taking control of everything including ISO and white balance. One day, I was chatting to a friend of mine who was (is) a full time professional photographer who asked why I was doing this all the time. When I gave my explanation (the usual, I want full control bla bla bla), he just laughed, and talked to me at length about aperture priority. I tried it, and immediately, the virtues he had told me about came real.

Let’s take a look at what aperture priority is, because understanding it will allow you to do what is important in photography and concentrate important aspects such as composition and being involved with your surroundings, instead of being fixated with settings. Of course there are times when you will still need to use manual settings, it would be silly to think otherwise, but using aperture priority, most of the time for most things is a game changer.

What is aperture priority?

Aperture priority, often abbreviated as A or Av on your camera’s mode dial, is a semi-automatic shooting mode that gives the photographer control over the aperture while the camera automatically sets the shutter speed and ISO to achieve a correct exposure. When used with Auto ISO, it creates a powerful and efficient workflow.

How it Works

In aperture priority with Auto ISO, you, the photographer, choose the desired aperture value (f-stop). This f-stop directly controls the depth of field, which is the range of distance in a photograph that appears acceptably sharp.  A wide aperture (e.g., f/1.8) creates a shallow depth of field, blurring the background and isolating the subject. This is great for portraits. A narrow aperture (e.g., f/16) results in a deep depth of field, keeping both the foreground and background in focus, which is ideal for landscapes.

Once you’ve set the aperture, the camera’s meter measures the light in the scene. Based on this measurement, it then automatically calculates and sets the appropriate shutter speed to ensure a balanced exposure. At the same time, the Auto ISO feature adjusts the sensor’s sensitivity to light. If there isn’t enough light for a proper exposure at the chosen aperture and the slowest shutter speed, the camera will automatically increase the ISO, allowing it to capture more light without needing a slower shutter speed. Conversely, if there’s too much light, the camera will decrease the ISO to its base value (e.g., ISO 100) to avoid overexposure.

This three-way relationship—you control the aperture, and the camera handles the shutter speed and ISO—is the core of the system. You have direct creative control over the aesthetic element of depth of field, while the camera intelligently manages the technical aspects of exposure.

Why Aperture Priority is Often Better Than Manual Mode

While manual mode (M) gives you complete control over aperture, shutter speed, and ISO, it can be a slow and cumbersome process, especially in situations where light conditions are constantly changing. Here’s why aperture priority, once you understand manual mode’s principles, often makes more sense for many photographers in general photography:

• Efficiency: Aperture priority is far more efficient. In manual mode, if you move from a sunny area to a shady one, you’d have to manually adjust at least two of the three exposure triangle settings (aperture, shutter speed, and ISO). In aperture priority with Auto ISO, you only need to confirm your desired aperture. The camera instantly adapts the shutter speed and ISO to the new lighting, allowing you to focus on composition and timing rather than getting bogged down in technical adjustments. This makes it perfect for dynamic situations like street photography, events, or travel.

• Creative Control Over What Matters Most: For most photographers, the most important creative choice is the depth of field. Do you want a blurry background for a portrait or a sharp landscape from front to back? Aperture priority puts that specific choice front and centre. Shutter speed and ISO are often secondary, technical concerns. The camera is better equipped to handle these variables quickly and accurately, allowing you to prioritize the creative aspect of your image.

• Intuitive Workflow: Once you understand the fundamentals of the exposure triangle from using manual mode, you’ll recognize that aperture priority is a streamlined version of that process. You’re still making a deliberate creative choice, but you’re delegating the tedious, reactive parts of the exposure equation to the camera’s powerful processor. It’s a “set it and forget it” approach that empowers you to react to the scene as it unfolds.

In essence, aperture priority with Auto ISO gives you the best of both worlds: the creative control of manual mode over the most critical setting (aperture) and the speed and convenience of an automatic mode. It’s the sweet spot for most photographers who want to create consistently great images without missing the moment.

Understanding exposure compensation

When you are shooting in aperture priority mode and you adjust your exposure compensation, you are essentially overriding the camera’s automatic exposure settings to either brighten or darken the image.

Here’s how it works:

• Aperture Priority Mode (A or Av): In this mode, you manually set the aperture (f-stop) to control the depth of field. The camera then automatically calculates and sets the shutter speed to achieve what it believes is a “correct” exposure.

• Exposure Compensation: The camera’s light meter is designed to average the scene’s brightness to a “middle grey.” However, in scenes that are particularly bright (like a snowfield or a beach) or dark (like a night scene), the camera’s “correct” exposure may not be what you want. This is where exposure compensation comes in.

• The Effect: When you dial in exposure compensation in aperture priority, you are telling the camera to adjust the exposure without changing your chosen aperture. Since the aperture is fixed, the camera will change the only other variable it controls: the shutter speed.

• Positive (+) Exposure Compensation: If you set a positive value (e.g., +1 EV), you are telling the camera to make the image brighter. To do this, it will slow down the shutter speed to allow more light to hit the sensor.

• Negative (-) Exposure Compensation: If you set a negative value (e.g., -1 EV), you are telling the camera to make the image darker. To do this, it will speed up the shutter speed to allow less light to hit the sensor.

In summary, adjusting exposure compensation in aperture priority mode gives you the ability to fine-tune the brightness of your image while maintaining control over the depth of field. It’s a powerful tool for situations where the camera’s automated exposure decision doesn’t align with your creative vision.

Conclusion

It is not big or clever to use manual control all the time, and anyone who has done photography for many years knows this. Of course, if you need manual control for a specific thing you do, then that is fine, but for most things you will getter, and more consistent results using aperture priority. I, like many, used to think that only shooting in manual mode, was akin to bragging rights as a photographer, but looking back, that was simply not true. It is all about knowing what to use, and when to use it.

If you have not tried aperture priority, give it a go. Once you have set it up correctly, and understand how it works and the times you may need to change to manual, or shutter priority, you will never look back. Most of all, you’ll never miss your exposure because the light suddenly changes when you are chasing your next photography target.