Someone gave me a canon 100-300 lens. I don't have it in front of me, but I think its f/4-5.6, and it has an ultrasonic motor. Also, its made in Japan, but aren't all Canon lenses made in Japan? It looks to be about 10-15 years old, and has a metal ring where it attaches to the camera body. I haven't bought a DSLR yet, but wanted to know if this lens is good enough to keep, or to sell and get something else for it. I'll admit I'm not very picky at all (I probably wouldn't know what to do with an L lens), but I don't want to use junk either (Which if Canon made it, its probably mediocre at worst). I'm just amazed someone GAVE it to me. I mean, its still good! So, if anyone has used this lens before (one of the Marks, I'm sure there's more than one), I'd like mini-review (a sentence or two).