I plan to write a post about the exposure triangle (three factors that affect the exposure of a photo), but to include them all in one post means it’s going to be a too long read. So, instead, I will divide them into three separate articles with a hope that you can understand it more easily. The first one is aperture.
So, what is aperture, you ask? To put it simply, it is an opening in a lens through which light enters the camera. As you can guess, when the lens is set to be wide open, more light will be allowed in, increasing the photo’s exposure. You won’t likely need that unless you shoot in low light situations or in an attempt to achieve certain creative effects (we’ll talk about it in the later section)
Aperture and F-Stop Values
An F-stop value reflects how wide the lens aperture is. It is shown as “f/n-number”. The larger the number, the narrower the aperture; the smaller the number, the wider the aperture. Confusing? I hope not. You see, it’s a simple math. As the dividing number gets larger, the resulting value gets smaller.
There are at least nine values on the scale that measures aperture. Here are they:
As you go down from one value to the next, you’re decreasing the aperture size by half, which also means you’re allowing 50% less light to enter the camera.Take a look at the diagram below:
Now, since 50% is quite big a jump, camera makers often squeeze in one to three more f-stops in between those values above. For instance, in between f/2.8 and f/4, you will likely find f/3.2 and f/3.5. With these, you can control the amount of light coming through the camera lens more flexibly.
Aperture and Exposure
So, now we know that aperture and exposure is correlated to each other, but how does the former affect the latter? Well, it’s obvious. As you set the aperture wider, you’re allowing in more light, which results in your photos being more exposed. Take a look at the images below. The ISO and shutter speed are controlled; only the aperture is changed to show how directly it influences exposure.
Any F-stop value from f/2.8 and lower is considered as wide aperture. It’s mostly used in low light conditions and indoor scenes.
Aperture and Depth of Field
In addition to exposure, aperture also affects depth of field. To explain what it is in detail would be too long and may distract you from our main topic here. So, let’s just be content with a short description from Wikipedia: “Depth of field (DoF), also called focus range or effective focus range, is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.” In other words, it’s a range in which an object is in-focus.
As of how it’s affected by aperture, well, wider aperture leads to shallower depth of field, which means less objects in the scene will be in-focus. This is how photographers get those attractive looking photos where the background or foreground (or both) is blurred and the main subject is sharp. It’s handy when you want to have a beautiful soft focus effect on your photos.
On the other hand, smaller aperture creates a deeper depth of field. You’ll find more objects on the scene looking sharp, which is exactly what you need when you’re shooting a landscape. Capturing a scene of a group of people can also use small aperture as it makes sure all faces will be in-focus, thanks to the deep depth of field.
The following diagram summarizes what I’ve explained regarding aperture and depth of field. As you shoot in manual or Aperture Priority mode, it’s important to keep such correlation in mind to get the intended look from your photos.