WOW- To davidc502 and JeffreyG, no measuring going on here. I have posted portraits in the 1ds thread and know the difference between the two formats. I thought it might be good idea for a post so we could see the type of look that a certain camera gives for certain subject. If you don't like it that is great, there are thousands of other threads to look at. You can of course add to the thread or indeed if you prefer make condescending comments. All is allowed
OK, fair enough. And I was a little grumpy so I clarified my previous.
But on topic - there isn't really a different 'look' between 1.6X and FF in the overwhelming majority of shots. Almost every single shot that can be made with a 1.6X format camera can be duplicated by a FF camera using a lens that is ~ 60% longer in focal length and an aperture that is 1 and 1/3 stops smaller.
There are two things that a FF camera can do that a 1.6X cannot:
1) Achieve just a bit thinner DOF when we get to the very fastest of lenses. So if f/1.2 isn't thin enough DOF for you on 1.6X then there is FF. But in my opinion the fast primes on 1.6X are often going to be fast enough.
2) Shoot very wide and very fast at the same time (as in the example photo below using a 24L on a FF body). Simply put there is nothing akin to the 24mm f/1.4 available for the 1.6X format.
And that (to me) is about it when it comes to the main difference between these two formats - lens selection. A 70-200 is a different kind of lens on a 1.6X than it is on a FF as far as functionality. There is nothing quite like the 24/1.4 available for 1.6X. Things like this.
But put a 50L on a 1.6X and an 85L on a FF and the resulting images will look pretty much the same, especially if we are not shooting both wide open.