I carry a DSLR on my backpacking trips. I use a Thinktank digital holster which holds my camera with lens attached and one extra lense. http://www.thinktankphoto.com/products/digital-holster-20-v2.aspx
I open the velcro flap and slide it over my backpack waist belt buckle. The holster has 2 D rings on the sides at the top and I attach adjustable straps here to the D rings on my backpack shoulder straps. This balances the weight between the waist belt and shoulder straps.
Easy to access your camera, the holster top opening opens away from your body. Comes with a rain cover if needed. I can still see where my feet are on the trail.