First off sorry for digging this old thread up. I was wondering how come nobody speaks of DOF comparison when using 1.6 or full frame.
i was thinking to use 1.4 aperture on 5D mk2 means the dof may be too thin for certain shots. Thus we lose light be moving aperture up to gain the dof.
However if we're to use 7D with 1.4 aperture we actually gain a dof advantage at that same given light.
If you find the DoF too thin on the 5D2, you can stop down and then up the iSO (to retain amount of light). 5D2 has a 1 stop advantage over a 7D (some insist that its actually 1.5-2 , but based on my exp , prolly just 1).
Bottomline, the 5d2 gives you more DOF options than a crop body like the 7D. Having the ability to have a very shallow DOF is an advantage not a disadvantage.
This is one major reason why the 5d2 tops over 7D portraits. You can have more background separation. You pay a lot for those 1.4s and 1.2 lenses, a full frame just maximizes their abilities.