You may not like what I do but I’ll share as food for thought. I’ve never purchased a “camera backpack.” I am an avid cyclist so I simply use an Osprey brand cyclist’s backpack that I’ve had for several years. Since it’s designed to pad your back from stowed items it has a fairly thick foam pad sewn inside. It does not have velcro compartment dividers like a true photorapher’s pack. I cushion lenses like a Nikon 300mm with an old thick wool sock. I can fit an ancient Nikon 800mm f8 122mm objective, the 300mm and a full frame Nikon body, gimbal head & a few filters, TC, cleaning supplies etc inside. I carry the tripod over shoulder with a sling strap. There’s no limit to your options. But I would suggest you go to a store with your typical load and try some out. Until you shoulder your load you won’t know what you find most comfortable. Would you buy a car sight unseen without a test drive? Happy hunting & good luck.

I have the Nikon 400m 2.8. It's a beast. That hood is the issue when trying to pack it for air travel. I purchased a cloth hood from lenscoat to travel with. http://www.lenscoat.com/travelhood-c-44.html. This makes the lens pack-able in a large bag that will hold my 2 dslrs, teles, and a couple of other lens for landscape that I carry on. The problem is at the other end and the field. This bag is barely big enough to house this lens with camera attached while hiking but will at an angle. I can fit another body in with say a 70-200 around that but not attached. The compromise is to wear the camera plus 70-200 lens during the hike or mount the camera plus 400 on the tripod over the shoulder with a bodypod for the hike. Whew! My large bag that will hold everything is a Tenba. My bag if I get to drive for the 400 with camera and hood attached is the Tamrac...which is slightly longer than the others. It definitely won't qualify for carry-on due to length.
Good luck with your decision!

Hi Goober,

You might take a look at the Manfrotto Pro Light Bumblebee 230 backpack. I bought it from Adorama via eBay. It fits the standard for use as carry-on luggage and is spacious, comfortable, and provides excellent protection. In my backpack I typically carry a Canon 5D4, a Canon 70-200 f/2.8, Canon 24-105 f/4, a Sigma 150-600 C, a Canon 600EX-RT-II, filters, batteries, and occasionally a Dell M6700 17-inch laptop. I have hiked (without the laptop) up to the 6,000 to 7,000-foot level of mountains on a two to three hour trek, often with very steep elevation climb, very comfortably and I am certainly no spring chicken. The lumbar support, waist and chest straps, and the ventilation against the back makes the journeys very comfortable. I have found it to be one of the best backpacks for getting around in the urban or the wild.

Check out these videos on the backpack:

Manfrotto Promo Video
https://youtu.be/IH8QFxszaO4

Thomas Heaton's Evaluation and Durability Tests
https://youtu.be/RPK4CbKTWJs

Matt Granger packing it full
https://youtu.be/klyQyxQl0tE