Don't forget the equipment itself is a source of heat, you should really allow it time to take on the temperature of your surroundings, this can take from 10's of minutes to hours depending how much metal/glass (and focal length) your using.

Even then you will never eliminate it totally as your generating heat from the camera.

Heat is anything warmer than your surroundings, -5 is warmer than -10 warm air rises even when its cold.

Yes John - I know - bearing in mind what I've already said viz no auto focus and no hand on cam or lens, and considering the rig weighs somewhere around 15Kgs can you come up with something that could cause this???

To me the whole images goes out of focus and I can assure you 100% that the focus ring never moved - so what else is left, has the sensor decided to have a flutter or what?

I'm clueless to it all - believe it or not that's why I asked the question, in the hope that a board full of my more experienced peers might be able to shed some light on the strange occurence!

Thanks

Andy

Sorry if I missed it but is there any kind of image stabilization on?

No John - the Sigma 500mm f4.5 prime is not an IS lens - if only it were that simple!!

Andy

Many thanks for the suggestions but it does now appear that was the hardware at fault - I eventually sent the XL2 into Canon for a look over and they have come back having found a number of problems, including the battery holder needing replacement. I should see the camera again in the next week having had its ills put to rights and a full service.