Ditto on ThinkTank. I use the TT International when carrying a 500mm + 2 pro bodies + lenses + flash, accessories, portable drives and 15" MBP, etc. A tip is to not use the Canon 500mm cap and get a Zeck lens cap instead (from naturescapes.net - saves space and easier to use in the field). Also consider getting the low profile 4th Gen lens collar foot, also from NS.
|_F0A5334-Edit_small by Dester Wallaboo|
from Open Air Fashion Photography
|Feed me, me, me, me, me by Denjw|
from Attention-Seekers in Nature