Originally posted by: fuzzybabybunny
You reverse mount a lens by doing just that; reversing it and mounting it to the camera body. You can do it right now; just take off your lens and hold the front end to the body, and you'll see that you'll be able to focus really close on things. To get a more secure mount, you can reverse mount it by simply getting something like this:
http://cgi.ebay.com/58mm-Reverse-Mount-...5QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
What it is is basically one side has threads that screw right into your filter threads at the front of the lens, and the other side mounts right into your camera body. When buying this make sure that its screw thread diameter matches the filter size of your lens. For the Tamron 17-50mm, it's 67mm so you'd need to get this:
http://cgi.ebay.com/67mm-Reverse-Mount-...5QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
ANY lens is reverse mountable. Since the Tamron 17-50mm is already sharp as hell the macro pictures should be the same.
I would recommend getting an external flash for macro though; it helps a lot in getting a fast enough shutter speed to catch these guys. Also note that reverse mounting for macro means you'll have very little working distance between you and the subject, I would say around 6 inches and closer depending on magnification, which goes up as you zoom to wider focal lengths.