Good to know NancyP.
Personally, I think there are two categories of photography and backpacks.
1. Serious and extended camping/hiking, etc
. This is 90% Trail Priority / 10% Photography
(regardless of the purpose of the trip or the amount of photo gear needed) because the person needs to live on the trail and be comfortable, healthy and hydrated for the entire time. They need to have good appropriate gear/boots/etc for the trip and be in good shape to handle the physical demands. Photography may be the reason for the trip but failure to properly outfit for the journey is courting disaster. Taking too much of anything, esp photography equipment, may literally break the hiker, the pack or both.
2. Light hiking to a major photography project/activity
. This is 80% Photography / 20% Hiking
and is likely a day trip or overnight journey, ideally in warm weather not too far away from the car and occurring in fairly hospitable locations. This is what I think photography packs are designed for. They are made to help carry a lot of photography gear a few miles max with no need for much more than a snack and some water for the person. They are designed with a lot of padding that I often find overkill since I don't plan to play kickball with the pack but it makes most folks feel better knowing they are carrying an extra 10 lbs of foam padding around all their gear. I do a LOT of scout camping, summer camps, and outdoor events. I have found that for what I do, it's easier to take a trunk in a vehicle with plenty of gear, individual lens cases, etc and put what is needed in a simple day pack and walk lighter. Someday I might get a photography daypack but they seldom hold enough to make it worth the high cost. You get some photo gear loaded into all the dedicated slots, etc and you have little room available for anything non-photography related. And it's heavy. And everyone sees you carrying around a big expensive photo pack. I look geeky enough already thank you.