Aperture is the last of the three major elements in photography (and has always been the trickiest one for me to wrap my head around). It’s the hole through which light travels and enters the camera, and adjusting the setting affects how big or small that hole is.
Aperture affects a photo’s depth of field — how much of the photo will be in focus:
- A small (or shallow) depth of field means less of the photo will be in focus and is created with a larger aperture (a bigger hole).
- A large depth of field means a larger portion of the photo is in focus relative and is created with a smaller aperture (a smaller hole).
For example, in this picture where the baseball pitcher is more focused and clearer compared to the crowd, a pretty large aperture was probably used. On the other hand, this one, where the pitcher and the crowd are both in focus, was likely taken with a smaller aperture.
Aperture is measured in “f-stops.” The range of my G12 point-and-shoot is from f/2.8 to f/8.0; high-quality DSLRs can have ranges from f/1.2 to f/22. Because these are fractions, a large aperture means the bottom number is actually smaller, and a small aperture means the bottom number is bigger.
- Large depth of field = small aperture = large denominator in f-stops.
- Small depth-of-field = large aperture = small denominator in f-stops.
Just like ISO and shutter speed, adjusting aperture has trade-offs:
- A smaller aperture (e.g., f/8.0) means you’re letting less light in, so you may have to increase ISO or slow down shutter speed to get a properly lighted, shallow depth of field.
- Conversely, a larger aperture (e.g., f/2.8) means you’re letting a lot of light in, so you’d want to decrease ISO or use a faster shutter speed to make sure the photo isn’t overexposed.
I had some trouble capturing images that really illustrated the concept clearly, maybe due to the limitations of my little G12 point-and-shoot, user error, or some combination of the two. A few of my attempts are below, but this post is also a helpful guide.
For this picture, I used a relatively small aperture and slow shutter speed:
In this one, I used a larger aperture and faster shutter speed, and the exercise machines in the background are blurrier compared to the first picture:
Fun fact about proportions: Going from one f-stop to the next doubles or halves the aperture. So if you know you are decreasing the aperture by half, you could make the shutter speed twice as slow as the original speed to reverse the effect on the amount of light being let in.