(Last Updated On: June 16, 2019)

Lens Focal Length

Focal Length is the measurement of the optical center of the lens to the film plane. Lenses come in different “focal lengths” and more and more you see mostly zoom lenses with a variable focal length (ie 18-55mm). A full extended zoom lens in this examples would be 55mm. Zoomed down the lens is 18mm.

Focal Length diagram

How Focal Length Affects Your Background (free video)

The Basics of Lens Focal Length (free video)

So what does the focal length change?

Let me show you 5 photographs that all have the same exposure, but different focal lengths.

28mm Exposure Control

50mm Exposure Control
50mm (normal)

100mm Exposure Control

200mm Exposure

400mm Exposure Control

All shots were taken from the exact same spot with the same camera body.

I simply doubled the focal length with each photo and used the same exposure (f16 @ 1/500 using Fujicolor 400). As you can see the longer the focal length the closer to the action we get. Also, as we get closer to the action and the focal length is longer there is a more narrow depth of field (background is more blurry). Ever wonder why that happens? Find out the physics of depth of field.


  1. How does this influence macro photography. I am having trouble getting good macro shots (achieving the narrow depth of field). I was advised to play with the focal length. I’ve studied aperture a lot over winter, but it is honestly a little hard (even with notes) to absorb.

  2. I am truly grateful for finding this website, clear, helpful, detailed, illustrated, I love it. Best part is, the comments reveal a team of people all helping each other out with patience and understanding.

  3. Focal length is not measured from the end of the lens. It’s measured from the optical center of the lens to the focal point. You can actually have a longer lens with a shorter focal length than a physically shorter lens.


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