...well in my case - nothing! There I was, sat taking photos of Steel Rigg on Hadrian's Wall when I loose my grip on my Canon 70-300mm IS USM lens and off it goes down the steep hill. I couldn't go after it as all my gear was set up, and just had to watch it tumble end over end out of sight. It had the end caps on and was locked and looked perfectly fine when I retrieved it. However, when it started registering f45 on my camera and trying to focus itself, I knew I hadn't got away with it. So, it's gone off to the repairer's today - wonder what they'll say ?? :-((
Well, I got back my lens, supposedly repaired and serviced/recalibrated for around £42. Unfortunately, it's still reading f45 - so it isn't fixed and has got to go back again. :-((
Doh - feel like an idiot now, apparently it's supposed to go to f45 at 300mm - you learn something new everyday ! Anyway, they were kind enough not to charge me for postage.