Much like the 85mm f/1.8, the Canon 100mm f/2 is also an exceptionally bright, short telephoto lens appropriate for both general photography and portraits.
Some portrait photographers feel, however, that 85mm doesn't give you quite enough of what you need in a portrait lens and they prefer the 100mm focal length of this lens because it gives them just a bit more compression.
Again, as with the 85mm, the f/2 setting allows for a paper thin depth of field, a good thing when shooting portraits.
