Camera packs

It's certainly not the only option and may be trickier to arrange than what interests you, but you could check out Aarn's offerings (which I've never tried myself). http://www.aarnpacks.com/ The standard Aarn design is to have balance pockets in front which they reckon is a better way to carry weight, which seems to have good reviews here and elsewhere though it can take some getting used to. For your specific purposes though, they have a particular design of balance pocket that's designed specifically for big SLR cameras and lenses... and the bonus is probably that you have more immediate access without needing to pull your pack off. (Look at http://www.aarnpacks.com/products/balance_pockets.html and scroll to the Photo balance pockets, keeping in mind you need to have one of the full Aarn packs to connect it to.) Give 'em a call if you're interested and have any questions or want to try something out. They're pretty cool people from my limited experience and might send you something to trial. It looks like there are a couple of distributors in the Auckland region if that's where you are.

I was going to reply but izogi has taken the words out of my mouth. I have just recently bought an Aarn pack but got the expedition pockets and not the photographers ones. I have to add that Aarn will lend you a pack to try out for a couple of weeks. It is an intergral part of their marketing as there aren't many in shops. Also my opinion of them is that they are well made and well thought out. There is no downside to having front pockets. They are low on your chest and don't get in the way at all. For a photographer it is all advantage having evertything handy while you walk. I don't actually think Aarn packs are as radical as they make out. I would compare carrying an Aarn pack to carrying a conventional pack with your thumbs behind the shoulder straps, like we sometimes do. The front pockets gently pull the shoulder straps forward so that, if you want, there is very little weight on your shoulders. However that weight does go to your hips and your belt needs to be well adjusted and tight, so there is no free lunch really.

ditto, ditto I've had an Aarn pack (Natural Balance) for 2 years (900km of overnight tramps) and, IMO, it's brilliant. Yes, the packs are designed for the weight to sit on the hips (and not around the hips like a conventional pack) - the waist belt is designed to fold over the top of the hip bone (ie over the iliac crest). Balancing weight between front pockets and main (back) section means that you carry the weight comfortably on your hips - no weight on the shoulders. Five of my tramping mates have now converted to Aarn packs - some of them initially rubbished the design but over time they've seen the benefits in others and have finally made the move - and are loving it. One friend would see a physio after every extended tramp - 1st tramp with the Aarn pack was a 10-day Central Tassie walk - she finished the walk laughing that the physio wasn't needed ! If you only need 20L plus camera space, the Mountain Magic 55 would easily meet capacity requirements - however, this model only takes the standard balance pockets, not the photo- or expedition- pockets. Take a look at Featherlite Freedom or Natural Balance if you need more volume. Although the Photo-pockets are designed specifically for DSLR gear (multiple dri-liners in each pocket), compare them with the Expedition pockets (larger capacity but one dri-liner per pocket) - you can always add an extra couple of small dry-bags.