When would one choose a 50mm f/1.4 over 85mm f/1.8 (or vice versa) for portraits?

Question

Say you are using a crop body, and you have both 50mm/1.4 USM and 85mm/1.8 USM lens in your bag. Now, you want to take a portrait where there is adequate light and space, and you have decided to take the shot at f/2.2.

Now I want to know which lens will be good to use to take such a shot, and why.

Answer

Both are certainly capable of taking the shot, so I guess you are looking for the differences. Obviously, you have to stand further with the 85mm to get the same framing but a few other things will change:

• The perspective will be more compressed on the 85mm. In general that is considered more flattering for portraits, particularly of non-Asian, since it makes the nose look smaller.
• There will be less depth of field at the same aperture on the 85mm, so you can blur out the background more. Of course you can open the 50mm much more to compensate.

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