What is Focal Length?

Focal length is really just the fancy DSLR term for the ability of your lens to ZOOM. If you've been using a compact camera for some time, you may know that the camera has a 3x, 5x or maybe even a 10x zoom.

People rarely discuss the focal length of a compact camera lens, but it's a fairly common term when you're talking about a DSLR lens.

Here's the gist of it:

• The focal length of a lens is expressed in millimeters
• Small focal length number ==> WIDE angle of view
• Large focal length number ==> TELEPHOTO angle of view

When you're using a wide-angle lens (with a small focal length) and you look through the viewfinder, you see everything from the foreground to the background. Wide-angle lenses are typically used for landscape photography.

When you're using a telephoto lens and you look through the viewfinder, you only see a portion of the scene in front of you, and that view is magnified.

Telephoto lenses let you take close-up pictures of subjects from very far away, which is why they are the lens of choice for wildlife photographers.

28mm	50mm	70mm	200mm

This is pretty straightforward, but gets a bit confusing when you start talking about zoom lenses, which have VARIABLE focal lengths.

Let's pick the typical kit 18-55mm zoom lens to use as an example.

• With the lens set to 18mm, the lens is at its wide-angle setting
• With the lens set to 55mm, the lens is at its telephoto setting

However, the same terminology could be applied to a 70-300mm zoom:

• 70mm is the wide-angle setting of the lens
• 300mm is the telephoto setting

The big difference here is that the 70-300mm lens cannot capture the same wide angle of view as the 18-55mm and the 18-55mm cannot zoom in as close as the 70-300mm.

Speaking of zoom, let's take a moment to talk about zoom POWER; this is how the zoom setting of all compact digital cameras is described.

To get the zoom power of any DSLR lens, divide the telephoto focal length by the wide-angle focal length.

Examples:

Exercise

• Pick up your camera - with whatever lens is attached - and set the lens to its wide angle setting
• Look through the viewfinder, and as you do, turn the zoom ring on the lens to gradually change to the telephoto setting
• If you have different lenses - with different focal lengths - note how each lens provides you with a different angle of view as you look through the viewfinder

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