Anyone ever heard of freelensing? My niece just posted on her blog about doing it and I have to say I'm horrified to think of removing the lens to take pictures!!! She's using a Canon 30D that I helped her to purchase her on FM.....it makes me feel like an accomplice to a crime! Her blog post discussed being out by one of the Great Lakes in freezing, windy weather - yikes!!! Wonder what her sensor looks like!!! Am also wondering if I should say anything to her Are my gut feelings right or am I overreacting?
Perhaps the lens will be dropped or the mirror box will get dirty, but I'm not sure what else is wasted other than time playing around. I'd use a TSE or similar lens if I wanted those annoying tilted focal plane effects, but I don't.
Freelensing works best with lenses with an image circle significantly larger than the sensor (e.g., something not wide-angle). Also, practice holding the lens against the mount, making sure you don't obstruct the mirror or make contact with the exposed rear element. If you are using EF lenses, another thing you can do is use the DOF preview trick to stop down the lens prior to unmounting it, which will give you some degree of control over the aperture; otherwise, a manual lens with an aperture ring can also work.
It's really not anywhere near as stupid or dangerous an idea as it sounds; it's just not a technique that lends itself to easily reproducible or consistent results. It's really about experimenting and embracing the occasional happy accident.
I would definitely NOT try freelensing with an 85/1.2L. Besides the danger of scratching such a large and exposed rear element, you can't focus if the lens is decoupled.