Exposure Explained

Exposure is one of the most fundamental concepts in photography. It refers to how much light reaches the camera sensor (or film) when you take a photo. Exposure affects the brightness, contrast, and colors of your image. A well-exposed photo will have a balanced distribution of light and dark areas, without being too bright (overexposed) or too dark (underexposed).

But how do you achieve the correct exposure? The answer lies in the exposure triangle. The exposure triangle is a way of understanding how three camera settings work together to control the exposure: aperture, shutter speed, and ISO. These settings also affect other aspects of your image, such as depth of field, motion blur, and noise. By learning how to adjust these settings according to the lighting conditions and your creative vision, you can master the art of exposure.

Let’s take a look at this depiction of the exposure triangle that I borrowed from this blog.

Credit: ActionCamera.blog

As you can see, aperture, shutter speed, and ISO are interrelated and affect each other. Changing one setting will affect the exposure and require you to adjust another setting to compensate for it. For example,

  • If you increase the aperture (smaller f-number), you let in more light and need to decrease either the shutter speed (faster) or the ISO (lower) to maintain the correct exposure.
  • If you decrease the shutter speed (slower), you let in more light and need to decrease either the aperture (larger f-number) or the ISO (lower) to maintain the correct exposure.
  • If you increase the ISO (higher), you make the sensor more sensitive to light and need to either decrease the aperture (larger f-number) or shutter speed (slower) to maintain the correct exposure.
Now, let’s discuss in more detail how each of these three components affect exposure.
 

Aperture

Aperture is the size of the opening in the lens that lets light into the camera. The aperture is measured in f-stops, such as f/2.8, f/4, f/8, etc. The smaller the f-number, the larger the aperture, and vice versa. For example, f/2.8 is a large aperture that lets in more light than f/8, which is a small aperture that lets in less light.

Aperture also affects the depth of field of your image, which is the range of distance that appears sharp in focus. I talk more about this on my dedicated page about aperture.

Shutter Speed

Shutter speed is the length of time that the camera shutter stays open to expose the sensor (or film) to light. Shutter speed is measured in seconds or fractions of a second, such as 1/60s, 1/125s, 1/500s, etc. The faster the shutter speed, the shorter the exposure time, and vice versa. For example, 1/500s is a fast shutter speed that freezes motion and lets in less light than 1/60s, which is a slow shutter speed that creates motion blur and lets in more light.

Shutter speed also affects the appearance of movement in your image. A fast shutter speed can capture fast-moving subjects without blur, such as sports or wildlife photography. A slow shutter speed can create intentional blur to convey a sense of motion or dynamism, such as panning or long exposure photography. Check out my post on shutter speed for a more info.

ISO

ISO is the sensitivity of the camera sensor (or film) to light. ISO is measured in numbers, such as 100, 200, 400, 800, etc. The higher the ISO number, the more sensitive the sensor is to light, and vice versa. For example, ISO 100 is a low sensitivity that requires more light for a correct exposure than ISO 800, which is a high sensitivity that requires less light for a correct exposure. In digital photography, this “sensitivity” is really an amplification of the digital signal, since the sensor has a fixed sensitivity to light.

ISO also affects the amount of noise or grain in your image. Noise is the random variation of color or brightness in your image that reduces its quality and detail. A low ISO produces less noise and a cleaner image than a high ISO. However, it’s important to note that modern cameras have improved their noise performance and can handle high ISOs better than before. Forcing a low ISO to reduce noise is not always the right decision and can have a negative impact on other, potentially more important, aspects of your image.

Check out my post on ISO for more information.

Balancing Aperture, Shutter Speed, and ISO

Armed with the knowledge of the exposure triangle, you might now be wondering, “How do I choose the right balance between all these settings?”. The short answer is, it depends on your creative vision! However, I will do my best to give some guidance and suggestions based on my personal experience. But before we continue, I highly suggest reading my dedicated pages on aperture, shutter speed, and ISO if you don’t already have a solid understanding of how these settings affect your image. With that said, here are some suggestions on how I prioritize each of these settings when adjusting my exposure.

ISO does not provide much of a creative purpose, so I typically prioritize ISO last. Modern digital cameras have impressive sensors with improved low-light performance, meaning that higher ISO values are much less noisy than they were in the past. For this reason, I don’t mind shooting at a slightly higher ISO if it means I can prioritize aperture and shutter speed, which both have more important roles in the overall image, in my opinion.

Prioritizing between aperture and shutter speed is dependent on what I’m shooting, but I typically start with aperture. Aperture affects the depth of field, which determines how much of the image is in focus. By setting my aperture first, I can ensure that I get my desired aesthetic.

Most of the time, I want everything in my image to be tack sharp. In these cases, I need to set the shutter speed to a value that minimizes motion blur (from either camera movement or motion in the scene). Thankfully, cameras and lenses these days have impressive stabilization, so camera movement is less of an issue. For long exposure photos, sometimes smaller apertures and low ISO aren’t even enough to compensate for the increased amount of light. In these cases, I like to use a neutral density (ND) filter, which uniformly lowers the amount of light that enters the lens.

Although balancing these exposure settings can be daunting at first, a bit of practice will help make the process more natural. Understanding how each of these settings contribute to exposure and the overall aesthetic of the image will help take your photography to the next level.

Using Camera Metering and Histogram to Set Exposure

Most cameras have some type of built-in light metering to help you set your exposure. I will cover this topic in detail in another post.

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