This photography rucksack is excellent if you have a reasonable amount of photography gear to lug around, or have a fairly large lens and want to carry other gear like your wide angle lens, lunch, waterproof jacket, hat & gloves. All the stuff you need when your out really.
This sack is big enough to hold a sigma 500mm f4.5 attached to a body, or the nikon 200-400mm f4 which is about the same size. I don't know about canon lenses, but I don't think it will fit the 500mm f4 canon or nikon with the body attached. As well as the sigma 500 I can also get it my 70-200 f2.8 VR, 18-200VR, and lunch! A tripod straps nicely on the outside, and there is plenty of room in the outside vertical pockets for plenty of spare batteries and memory cards. Inside the lid are clear pockets which you can fill with filters, film, blower, all the usual bits and bobs! There is also a large front pocket with a 'waterproof' zip that is big enough to hold a laptop. If you need to carry more, then you can get extra pockets that strap on the sides too, or use your own straps to attach a hide etc.
There are loads of adjustable dividers, I've taken most of mine out as they aren't needed, but they are very useful if you have more small stuff rather than big lenses.
With all this gear in its quite heavy, but it's still comfortable to carry with the well padded shoulder and waist straps. It's well made, and reasonably waterproof, although could do with a raincover if you are going to be in the rain all day.
This bag also meets carry on luggage requirements for most airlines, I've not tried this out yet although the measurements do add up so I am hopeful. I'm off to the USA to photograph a friends wedding in 4 weeks, so I will know then, but to be able to fit all my camera gear and my laptop in one bag will make life so much easier.