Focal length, measured in millimetres, sets how much of the scene a lens shows. Shorter focal lengths show more; longer ones magnify distant subjects. The figures below are full-frame equivalents; see crop factor for other sensors.
- Under 20mm, ultra-wide: landscapes, interiors, the night sky. Stretches anything close to the edges.
- 24-35mm, wide: travel, street, environmental portraits, video of yourself.
- 40-60mm, standard: close to how we see; everyday, street, food.
- 85-135mm, short telephoto: flattering portraits with blurred backgrounds.
- 200-400mm, telephoto: sport, events from the back, wildlife in parks.
- 500mm and longer: birds and shy wildlife, motorsport.
Zoom or prime?
Zooms cover a range and save swapping lenses. Primes have one focal length but are usually brighter, smaller and sharper for the money. A good first setup is a standard zoom plus one cheap fast prime such as a 50mm f/1.8.
Perspective
Focal length doesn't change perspective on its own; your distance from the subject does. Telephoto lenses look "compressed" because you stand further back, which is why 85mm portraits look more flattering than close-up wide shots.