Focal length is an optical lens property, normally stated in millimetres.
Use it to understand framing and compare lenses on a given sensor format.
With sensor format and position fixed, a longer focal length gives a narrower field of view and a larger subject image. A shorter one includes more of the scene.
From one position, photograph a building at two focal lengths and compare the frame boundaries.
Focal length is not the physical length of the lens. Sensor format also determines the field of view.
Follow a connection to understand how these ideas fit together.
A longer focal length narrows the view on a fixed sensor.
Multiply the physical focal length by crop factor to describe framing equivalence.
One fixed focal length defines a prime lens.
Operating optical zoom selects another focal length within the lens range.
Compare changing the lens setting with changing where you stand.
Source check: . This records a check of the supporting references; it is not an expert endorsement.
With sensor format and position fixed, a longer focal length gives a narrower field of view and a larger subject image. A shorter one includes more of the scene.