K-5 not focusing in the cold?

Maybe (just maybe) some of the lubricant in the lens turned to a rubbery "goo" in the cold. If so, focusing by hand would be harder than usual. It might be worth putting the lens in the freezer (in a sealed plastic bag) for a couple hours and verify focus smoothness. If it is then stiff, I would try to have the lens replaced, preferably by one with a significant difference in the serial # to get rid of the problem.

Hi Yves

Thanks for taking the time to reply and suggest a test.

Sorry, I should have explained more clearly. It wasn't that the lens didn't focus, it actually focused backwards and forwards, but the problem was although it claimed to have locked on the selected point, when viewing the photo it clearly hadn't. I tend to aim the centre point on the part of the picture I want to focus on then re-compose so I always control exactly where this point is. As I was using a bloody big bridge at the time I hope I can rule out user error!

Having thought about it further, am I right in thinking that the drive for the lens is contained within the camera? If so, could it be the body with the problem maybe?

I will report back when it's cold enough to test again. I'm not sure how I feel about putting it in the freezer !

It sounds more like the lens trying to lock onto a point of low contrast or even the reflection. If it is the reflection then river would not be in focus but the building in the reflection would be.

Can you post an image to see if this is the case?