Thinking about the jump up to a 5D Mark II from my 40D. I use my UWA Tamron lens quite a lot, but almost all of the time at the 10mm end rather than anything else. What's the best equivalent lens I could replace this with? It's mostly tripod work so don't need a massively low F-stop lens. The 17-40mm F4 L might be stretching the budget a wee bit too much.
