Hi,
due to my new work I have access to some pretty cool new photo gear including some great lens's. One I was playing with is the canon ef 70-200mm f2.8 l is usm. On a 5D mk3.
My question is this.....if the lens is fixed at f2.8, what effect will changing the F stop on camera have? trying to get my head around it. As my tests shots were at F8 and look great.

thanks in advance.