What is a portrait lens?
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There was a time when zoom lenses were not of sufficient quality to be used for portrait work; certainly not for any serious professional, anyway. It is a generic term (which probably was coined even before that) because a portrait lens focal length depends on the film format being used. 80 mm was about right for 35 mm film, but 105 was OK, being slightly long. I disagree with the notion expressed above that anything around 50 is OK for 35 mm film; it's too short. As for 120/220 film, portrait begins at around 150 mm, so you can see what I mean by "portrait lens" being a generic term. Also, when using longer focal lengths, depth of field is less when all other factors are equal. Therefore, smaller f stops such as F8 are required, not larger, so I don't see the point about that either. For 35 mm, an 80 mm lens at F2.8 at ten feet provides a depth of field of approximately 9 inches. This is not enough to render the complete subject in focus (from one shoulder to the next) in a 45 degree pose.
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