I've had a Canon backpack for a few years and finally pushed it over the limit this weekend. I was already wearing a hole in the bottom, but I just broke the zipper from over stuffing it. Lucky for me, I heard the bag unzip and was able to stop all my gear from hitting the ground.
The bag is not made of the highest quality materials and it is uncomfortable to wear for long periods of time. The one thing in it's favor is that it holds a lot of gear.
Here it has a 5D II with 24-105 attached, a 17-40, 70-200 f/4 with hood reversed, 430EX on top of a 580EX, 50mm f/1.4, 100mm f/2, and a 1.4x TC on top of a set of Kenko extension tubes.
The front pocket holds my 14" tall Benro Travel Angel and my Camelback water bottle. I certainly wouldn't mind a backpack where I could put the tripod and water bottle on the outside (one on each side) of the pack and use the second pocket for more gear instead.
All this stuff is probably a little more than it should hold, which is what led to it busting open on a hiking trail this weekend.
What else will comfortably hold all this stuff? I have a Think Tank Retrospective which I love and use more often than any of my other bags. I looked at their Streetwalker backpacks a while back, but they seemed very narrow and deeper than necessary. I wasn't able to try them with any gear inside.
I have a Lowepro Micro Trekker and Pro Runner 200 AW. These bags are very well made, but are both too small for all the gear I want to put in them. Both are also very stiff and rigid, and I find them uncomfortable to wear. The shoulder straps always seem a little tight no matter how much I loosen them, and the packs sit very high on my back.
These are the only bags I have tried. I don't have any local camera stores and can't do any bag shopping or comparisons. What's out there that is better made than the Canon but will hold the same amount of gear?
I probably wear it fully on my back half the time and hanging on one shoulder the other half of the time. I almost never use the extra straps for the waist and chest.
I just saw this Incase DSLR Pro Pack




