ok first impression, this is a pretty good motorsports camera, i had on the 70-300 f4.0-5.6 L most of the day, you can use all 61 focus points with this lens, but not in all configurations, those are reserved for the 2.8 lenses, although the straight f4 lenses also get most of the crosspoint configuration. there are even a bunch of tables , A-H, in the manual listing what options each lens has. ; unfortunately i was shooting through a catch fence and the focus works so good that without thinking i set up in my usual f8 and be there, well i should have opened up as wide as i could because most of my shots have a beautiful fence right up there in your face. on the plus side the fencing is all crisply in focus. i had given up shooting most motorsports with the mk2, the motorcycles i have infield access so no fence in the way. not to worry, more racing next month, and now that i know the mistake i won't make that one again. colors are great, the bigger lcd is nice, mirror lock is still a menu item, but only 1 layer in, not the drill down to custom function that the mk2 is. still lot's more to learn, i spent the ferry ride to new london reviewing the manual, spent about 1 1/2 hrs on it last night, so i still have some more to learn. you can really customize both the quick menus and a lot more with the dials, so down the line i see being able to go back and forth among 3 different custom setups and changing base stuff on the fly much easier and quicker. the 6 shots per second rate is a real step up for motorsports, i think even dr jim would be pleased, he could hold multiple title belts in the cf card lion king events, 8,16 and the real heavyweight division, the 32gb cards.
one thing i just learned, lightroom 4 does not support the mk3, but they have 4.1 out as a release candidate, i guess that's more retail ready than a beta, so i just downloaded it for the mk3 raw support. those of you who use LR4 will be auto notified when the update is released, i found out about it when i did a quick google search about mk3 raw support.
i will have to go to sleep soon, so within the next couple of days look for some sample images with some commentary.