Focal length is one of the most important photography terms for you to understand because it informs you about the size of the lens - an important feature when buying glass for your camera.
Not only that, but understanding focal length also means that you understand what a particular lens is best suited to do.
That being the case, here’s a quick primer on understanding focal length.
Focal Length Defined
If we break focal length down to its simplest concept, it refers to how zoomed in your photos will be.
That is, the longer the focal length (the higher the number), the more zoomed in the shot will be.
For example, in the image above, which was taken with a long telephoto lens, you can see how there is little else in the shot other than the subject.
Contrast with this image, which was taken with a short wide-angle lens.
Notice how the primary subject is just one part of the shot, with much of the surroundings incorporated into the frame as well.
These are examples of how focal length impacts your photos, but what exactly is focal length?
To define focal length is to understand how it is measured.
While many photographers mistakenly believe focal length to be the measurement of a lens from front to back, this is not accurate.
Instead, focal length is the distance between the point of convergence of light and your camera’s sensor.
If that’s confusing, don’t worry - just remember that the longer the lens is, the longer the distance will be between the point of convergence and the sensor, and the longer the focal length will be.
So, in the image above, the lens on the far left has the shortest focal length; the lens on the far right has the longest focal length.
Types of Focal Lengths