Any macro lens would be great for portraits. In fact, if macro lenses have a fault, it's that they're too sharp for portraits. (Sometimes, you don't want every pore, facial hair, and blemish showing up in a portrait.) Anything from Canon's 60/2.8 and Tamron's 60/2.0 through Sigma's 70/2.8 to Tamron's 90/2.8, would do well. And if you've got room to back up (or you want to shot what looks like a passport photo) you can go with Canon's or Tokina's 100/2.8 or Sigma's 105/2.8.
The 50/1.8 is a little too short for head & shoulders portraits, but it works well for couples portraits and environmental portraits.
- The lens is the thing.
- 'Full Frame' is the new 'Medium Format'.
- "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.