Macro lens recomdendation

I work for a Dermatologist and we take picture of patients for a variety of reasons. We use a DSLR at my recommendation. We now do hair transplants and we'd like the ability to take up close shots of both the donor site and graft site. I don't know much about how macro lenses work in terms of focal length and magnification. Can anyone help fill me in on the particulars?

Assuming your equipment list is the clinic's list (i.e., APS-C camera)...

Canon 60mm is affordable and very good. Tamron 90mm is also very well regarded. So is the Canon 100mm, both without IS (more affordable) and with (L and more expensive). All will do 1:1 macro (the image on the sensor is equal to the object photographed).

Really, I think the key for what you're describing is a good, not necessarily great, macro lens, and a good ring flash. Lighting will likely be far more important than the lens.