What is focal length and how does it affect my photos?

Question

What is focal-length? Are focal-length and zoom synonymous? How does the focal length of a photo affect it?

Answer

Focal length is a measure how the lens focusses the light into a point. When light enters a 50mm prime lens, the light converges into a point the camera sensor after 50mm.

In addition the focal length determines the magnification of the object you photograph. A long lens (e.g. 300mm) magnifies the images a lot (useful for birding) while a short (wide angle) lens (e.g. 20mm) is useful for indoor pictures or landscapes.

Zoom usually means the focal length of the lens can be changed.

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