Camera backpacks are versatile tools not just for hiking photographers but also for photographers who need to bring a lot of gear to a shoot. There are a lot of options on the market these days. The Kata R-104 is a mid-sized bag suitable for a day hike carrying a dSLR body, four to five lenses, plus other accessories and a tripod. It also has a pocket for a 17-inch laptop (or smaller).
The Kata R-104's designers appear to have put some thought into the conditions your typical hiking photographer experiences. It's made of waterproof cordura nylon, has lots of padding, plus it comes with its own rain coat to help protect your camera from the wet. Its zippers are designed to seal out trail dust and its heavy plastic zipper pulls are large enough to be manipulated even if you're wearing heavy gloves.
While this bag will carry a day's worth of gear, it still meets airline carry on regulations (as of this writing). Its exterior dimensions are: 14.2" long, 10.6" wide, 20.9" high.
This bag can serve as both a camera bag and/or a video bag.