What is a portrait lens?

Question

I hear this term used pretty often. Does it refer to a specific focal length? Or very low F-number? What does a lens need to have in order to be considered "portrait lens"?

Answer

Generally speaking a portrait lens is a moderate telephoto (for 35mm film, maybe something in the range of 85mm to 135mm) with a moderately wide aperture (again for 35mm film, f2 or so).

As to why telephoto, a longer lens allows the photographer to fill the frame with the subject's face/shoulders without the apparent distortion of features you would get from being close to the subject with a wide angle lens. Telephoto and a wide aperture also helps reduce depth of field.

Note -- it isn't unheard of to use 180mm and 200mm lenses (35mm film) to take portraits, this tends to flatten the features a bit which can be an agreeable effect.

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