Tamron 17-50 vs Canon 50MM?

You are loosing about a stop and a half of light and sacrificing a bit of optical clarity. You are gaining some additional flexibility in how you compose a scene because you can zoom out. As a walk around lens, I would probably pick the 17-50 over the prime. I have a Tokina 28-80 f/2.8 as my walk around lens, and I like it a lot. If I were going to shoot some portraits, I would probably use the prime because it gives me that extra ability to blur the background and it is a tad sharper.

Here are the two lenses side by side:

http://www.the-digital-picture.com/Reviews/ISO-122...

The Canon is a fair bit sharper both wide open and stopped down. Of course, you could sharpen the Tamron, and you probably would not notice the difference unless you were shooting side by side, but in situations where I was going to use a 50mm lens anyway, I would use the Canon.

I have both of them and they are awesome. I use the 50 mostly for portraiture work. it is indeed very sharp since is is a prime lens with no zoom capability. it is built to work best at one focal length only. I use the 50mm more than the 17-50. for you, why replace them, keep them both!

Why replace? Just keep both! There are some test images for the Tamron here

http://www.the-digital-picture.com/Reviews/Sample-...