I'm curious about the advantages of shooting full-frame versus shooting crop. I've read various assertations that switching from a 40D to a 5D is like upgrading all of your glass, that a crop body gives you extra "reach" when using telephoto lenses, that you'd get similar quality shooting with a crop body as you would shooting full-frame and croping in post, and that the real image quality difference in full-frame comes when you shoot at high ISOs. So which, if any, is it?


I'm pondering what I'm saving my money up for...not in the immediate future, but probably a few months down the road. Among other things, I do a lot of airplane photography...say I took a picture of a plane with a 300mm lens and the plane filled the frame on my 40D. Now, say I took a picture of the same plane with the same lens at the same distance with a 5D and cropped it in Camera Raw such that the plane filled the frame. Which picture would be sharper?


(I don't shoot at high ISOs, but I do quite a bit of landscape/cityscape shooting where the more detail the better, so I'm already fairly certain a full-frame body would make that look nicer.)