I rented a 6D camera body to take helicopter skiing in Canada. I brought my 24-105 f/4, 40 f/2.8, and my 50 f/1.8 lenses. I found the autofocus to be slow with all 3 lenses, especially in lower light. I really experimented by changing many of the autofocus parameters and resetting the rental body to factory settings to make sure nothing was amiss. I found the 6D autofocus to be for the most part as good as my Rebel 550D with each of my lenses. I was really disappointed because a want a new body to replace my Rebel. Lensrentals.com checked the 6D and found it up to factory specs. Looks like I may have to pony up for the 5D m III. Does anyone think the climate and elevation had anything to do with the slow AF? Or does the 6D really have a mediocre AF?