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Track 1 · Exposure2 min read

LESSON 05

Focal length

The number on the lens, in millimetres. It decides how much of the scene fits into the frame.

HORIZONTAL ANGLE OF VIEW ON FULL FRAME

Five nested wedges from one point: the angle of view of 24, 35, 50, 85 and 200 mm lenses on a full-frame camera, from widest to narrowest.

What the number means

Focal length describes how strongly a lens bends light, in millimetres. For distant subjects, a longer focal length magnifies more and takes in a narrower angle; a shorter one takes in more of the scene and shows it smaller.

Wide, normal, long

On a full-frame camera, a lens of 35 mm or shorter is called wide-angle, and 50 mm is the usual normal lens, the one whose view looks natural. Much longer lenses are long-focus lenses, often loosely called telephotos.

Where you stand changes perspective

A wide lens used close up makes near things large and far things small, which can stretch a face or make a foreground bold. The lens itself does not bend perspective; it makes you stand closer or further away, and the distance does the rest.

Smaller sensors crop the view

The same lens on a smaller sensor shows less of the scene. To compare, multiply by the crop factor: a 50 mm lens on a sensor with a crop factor of 1.5 frames like a 75 mm lens on full frame.

Try it today

  1. 01Pick a subject with a background: a person by a tree.
  2. 02Shoot it close up at your widest focal length.
  3. 03Zoom to your longest and step back until the subject fills the frame the same way.
  4. 04Shoot again from there.
  5. 05Compare how large the background looks in each.

Figures from Wikipedia, 'Focal length', 'Wide-angle lens', 'Normal lens', 'Telephoto lens' and 'Crop factor', read 2026.10.16. The angles in the drawing are worked out from the frame width and the focal length (2 × arctan(18 mm ÷ focal length)). The steps under Try it today are working practice, not a standard.