I'm asking for this guy I know who might have accidently taken off his lens while his camera was on for about 4 seconds. His XL1 may not have been on, he's not sure. How much bad stuff may have occured to the camera if this was the case?

The proof's in the pudding; how did the camera image after he put it back together? Color shifted? Exposure blown-out?

As long as the camera wasn't pointed toward a very bright subject it's probably ok. But definitely not a maneuver to be repeated.

I'm not sure actually if he had any immediate effects. I didn't go into details about it. Would any effects like that be permanent, or once the camera was shut down, would they reset?

Even if it looks fine, should there be any worry of sublte damage to the CCDs?

All I know is it would have happened inside, so that would limit the light. Probably.

I would imagine that any damage would appear immediately. I think CCD's are relatively robust within reason.

I've removed the lens with the camera on a few times to no ill effect. All you have to do is re-colour balance and fix a few other camera settings, probably depends on which mode you're in at the time. Since the camera is designed to allow the removal of the lens I would expect they designed the camera accordingly.

The CCD's are designed to accept light collected by the lens and focused on the image plane...ie the CCD itself. Diffuse light, that is to say, unfocused light, won't hurt the CCD's at all.

The book says that the camera should be turned off when removing or attaching the lens (page 9 XL-1 Instruction Manual). It is a shame its on page 9 because Canon shows how to attach and remove the lens on page 8!

Another thing if you are getting the flashing "lens" indicator and are using either the EF or extender w/o a lens mounted, you will also get this indication.

http://www.canondv.com/downloads/manuals/ins_xl1.pdf

So, "this guy". Was it you?

I wasn't going anywhere near THAT question, Keith. <g>

Nope! If it WAS me, I would have phrased the question "SO this MORON I know..." :)

Actually I haven't had to change lenses at all since I got that second XL1 body from Ken. However, I did get quite worried about my first camera, because I know I've done this in the past without thinking about it.