I just returned from a 4000km round trip using my van as a camera shooting 24"x32" tintypes. I was using an 890mm Apo Nikkor that has a huge image circle at portrait distances and still covers 20x24 at infinity. I paid $350 for the lens.

You can see some of the plates on my blog if you're keen

http://craigtuffin.tumblr.com/