DLSR Backpack for climbing half dome?

I'm going to be climbing Half Dome in Yosemite in the Spring and I'm looking for a good DSLR backpack. I will be carrying my Nikon D90 with the 18-105 mm kit lens, an extra 55-300 mm lens, and an extra battery. I will also need room to carry a little food (my husband can carry most of that) water, and a light rain coat just in case. I was thinking something with a laptop section would work and I could slip in a hydration pack ( i'll make sure to take waterproofing precautions). I was looking at the Tamrac Adventure 9 online. I'm 5'2 and 120 lbs though I was wondering if that pack would be too big for me to climb half dome with for my first time. Anyone out there with that bag? Or any other suggestions?

I have a suggestion (I used to be into climbing, taught it for a while and sold mountaineering gear for a number of years. Also had a couple of boyfriends who did big-wall climbing, including El Capitan in Yosemite, and a number of friends who are professional outdoor photographers and what I will suggest is similar to what they use.

Look at the Seal Line Urban pack in the Large size:

http://www.google.com/...EgQ8wIwAw#

Though it was designed for urban cycling commuters, it has the basic tried and true design used for years for big wall climbing packs (like those made by Patagonia and Karrimor) -- a simple large single compartment with clean lines, a good harness with sternum strap and no bulky and restrictive padded hip belt. Best of all it is based on Seal Line's kayaking dry bag designs so it is very rugged and totally waterproof -- you could sink it in a lake and everything inside would stay completely dry. I know this to be a fact because I use Seal Line drybags for sea kayaking.

It is also a good size for a woman at less than 15" overall back length -- it will not interfere with your climbing mobility and at 37 liters volume will have lots of room for your camera gear and food. The rubberized fabric is very tough and will add some shock protection. Also get the smallest padded modular bag (like one of the Lowe models) that fits for the camera stuff and tuck it inside the Seal Line bag to add cushioning protection for the components. I would add an accessory cord to the camera case (with small mini-biner snap clips on each end) so I could tether it to the pack or my harness when I took it out.

Most of the DSLR packs are too restrictive and have too many straps, zippered pockets and other vulnerable components for climbing in such an exposed situation. All that hardware gets in your way and will allow rain to penetrate and potentially ruin your gear.

Here's a link to some outdoor photographers discussing how they carry their cameras that might help you.

http://photo.net/nature-photography-forum/00EbHo?start=10

I have the tamrac evolution.
http://www.bhphotovideo.com/...Search=yes

what's nice is you could cross the straps over your body making the bag impossible to come of