Ok, I had to google this one, as image quality is paramount in our end of the market, and I was concerned that maybe we weren't getting the best from our cameras.
So, for anyone else who's interested, here's what I've come up with...
Canon DO compress their RAW files - but it's not a jpeg compression, it's a proprietary lossless algorithm, so there are not artifacts caused by this compression. (Confirmation of this on Canon's website http://consumer.usa.canon.com/ir/con...=8772&pageno=2
) The only jpeg involved is the tiny thumbnail.
RAW + Jpg is a different setting entirely - and gives 2 files - a normal jpeg, and a normal CRW.
There is nothing you can change in camera to affect the compression on a CRW file.
Hope that helps to clarify it for anyone who's interested. It certainly put my mind at rest.