Excerpt from Scott Kelby's Digital Photography book, Chapter 3, The Truth About Lenses—What Makes It a Portrait Lens?
What Makes It a Portrait Lens?
Some types of lenses are called portrait lenses, so I am often asked, ‘What is a good portrait lens?’ That is a good question—and one that, as is often the case with lenses, has no clear answer. I would say that a portrait lens is a prime lens (so it cannot zoom) between 85 and 105 mm.
But there is a problem (and this is where the ambiguity comes in). Earlier, I discussed crop factor and full-frame cameras. So an 85mm prime lens on a regular, non-full-frame camera is closer to a 120mm lens, right? See what I mean? The lens compression produces more flattering shots.
(I showed two photos side by side for comparison.) That is why you see so many fashion and portrait photographers using 70-200mm lenses, usually working around 200 mm for photos of faces and head-and-shoulders shots. (Especially if the model has dandruff. Sorry, I could not resist.) I have photographed with an 85mm lens on a full-frame camera, but I did not think it looked as good as an 85mm lens on a regular camera. The 120mm range simply suits my style better.
If you use a telephoto zoom, try both and decide which one you prefer. I only want to make clear that you do not necessarily need to buy a portrait lens—whatever that may be—to create professional portraits. Modern zoom lenses do an excellent job, and as long as you stay above 100 mm, you will be pleased with the results.
Source: Scott Kelby's Digital Photography book.
