The focal length of a camera determines the framing of the scene and how large individual elements will be.
The focal length is measured in mm. A physically large lens often comes with a longer focal length. However, the focal length is not a measure of the length of the lens. It is a measure of the distance between the camera’s sensor and the convergence point of the light-rays moving through your camera.
Together with the aperture, the focal length is the main consideration in choosing lenses. Continue reading for a detailed explanation of the two effects different focal lengths have on the image.
The angle of view determines how much of the scene you can capture.
A short focal length like 24mm has a very wide angle of view. Short focal lengths let you capture wide panoramas or enable you to fit more of the scene into the frame while in constrained spaces.
A long focal length like 200mm will capture only a fraction of the same scene. Think of it as a zoom. Where 24mm could capture a subject as well as the landscape surrounding them, 200mm will narrow the frame down, cropping-out everything but the center of the scene.
Compression helps you control the size of individual elements within the frame.
Think of your image as a set of stacked panes. Depending on your distance to the subject, they will move farther apart or closer together.
And yes, you heard correctly. The deciding factor for compression is your distance to the subject. The focal length just helps to fill the frame. If you move far away, you will have to compensate with a longer focal length to retain your original frame.
So how does compression take shape in an image? Let’s look at the first illustration. We are using a wide lens, something around 24mm. We are standing just a few steps away from our subject, the pyramids are way off in the distance. Being close to your subject with a wide lens will spread out elements of the scene and enable the viewer to feel the space.
For the second illustration, we walked far away. The distance between us and our subject is now as long as the distance between our subject and the pyramids. to zoom back in and retain the framing of the first illustration, we switched our wide lens to a much longer lens, something like 200mm. Being far away from your subject with a long lens compresses elements of the scene. This results in a flat appearance that will diminish the spatial dimensions of the image.
Both of the effects are neither good nor bad. They are both tools for us to experiment with and make the right choice for what we are trying to accomplish.
You have probably noticed that images you take on your phone with the front-facing camera, tend to not turn out in your favor.
Take a deep breath. It's not you. It's your lens, and also its proximity to your face.
To fit you and your friends into the frame, manufacturers opt for wide-angle lenses on the front of their phones.
Unfortunately for our self-esteem, wide lenses do the same to faces as they do to landscapes. They decompress and magnify all the wrong parts. That’s why when shooting portraits, we usually opt for long focal lengths like 85mm.