Keys to Composition: Aperture

Have you ever wondered how pro photographers get that beautiful creamy look in the backgrounds of their photos? Ever wondered how landscape photographers manage to get such sharp detail throughout the entire frame? Well today we're going to talk about the aperture setting on your camera, what it is, what it does, and why it's important.

Aperture affects more than just exposure

When taking photos, there are three main things that affect your exposure; Aperture, Shutter Speed, and ISO. All of them affect your images in different ways. Shutter speed determines how long your shutter is open and can either allow you to freeze the action in your frame, or to get artistic looking motion blur. ISO affects the sensitivity of your sensor to light, and can allow you to shoot in darker environments, but at the cost of loss of detail (how much loss depends on your camera). Today, we're going to look at aperture setting, and how that affects your images.

First of all, look at both of these images that I took while shooting my short film, The Fall, in Los Angeles.


Notice how out of focus the background is in the F/2.8 photo vs. the one shot at F/10. That's because shooting at a lower aperture results in a shallower depth of field which narrows the plane of focus, while shooting at a higher aperture results in a deeper depth of field which keeps more of the image in focus. This is also affected by focal length and distance from your subject, with longer focal lengths compressing your depth of field and shorter focal lengths expanding it, while getting closer or farther from your subject will do the same respectively.

Changing the F-Stop, as it's called,  has the added effect of letting more or less light into the lens. Lower apertures let more light in, while higher apertures let less light in.

"But Tim, that makes no sense. Shouldn't the higher number be letting more light in?" Great question. You would think so, but no. It goes back to how  the F-Stop is calculated.

So how does it work?

The aperture of a lens is made up of several diaphragm blades like those pictured at the top. Those blades can open or close to create a larger or opening, similar to how the pupils in your eye expand and contract. The F-Stop is calculated as a ratio of the size of the aperture relative to the focal length of the lens, which means that the larger the ratio, the smaller the physical opening. If you want to learn more about the technical side of it, there's an excellent explanation here.

The most relevant excerpt:

We say that a lens has an aperture of f/4 to mean that the hole is 1/4 the focal length. So a 50mm lens (standard in 35mm format) at f/4 will have a hole 50/4 or 12.5 mm across. At the same aperture number, a 100mm lens will have a hole of 100/4 or 25mm diameter. That gives the longer lens a hole with four times the area, so it can capture the same energy from an area of the scene that is four times as small.

So why does it matter?

Being purposeful about your aperture size can have a huge effect on your photography. I myself shoot almost exclusively below f/4 because it allows me to easily separate my subject from the background and it gives my photos a polished look. Plus, it makes it so much easier to shoot in low light, which I often have to do for my work.

Shot at F/1.2
Shot at F/1.2

This is just my aesthetic, and there are plenty of reasons why you might want to use a higher aperture. Perhaps you are shooting landscapes and you want to capture detail throughout the entire scene, or perhaps you want to want to get close to a subject while still keeping them in focus. Those are both situations where you might want to use a higher aperture.

Keep experimenting with your aperture settings, and figure out what works for you! Perhaps you'll find that you like using smaller apertures like me, keeping your subject in sharp relief, while blurring everything else. Perhaps you'll find that you enjoy revealing detail from background to foreground. There's validity to both approaches. The important part is to get your camera off automatic and to start shooting! So get out there and have fun!

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