I have been using this backpack for a number of months now so I thought I should write a review of it. Most of this review I already did in swedish a while ago, for the swedish photography forum www.fotosidan.se
And here I am illustrating it with bad photos from my compact Canon IXUS.
To start and to put it simple, this backpack is simply better than anything else that I've either had or ever looked at. The 3 largest backpacks in F-stop's Mountain Series (Loka, Tilopa BC and Satori EXP) can be described as being empty shells, and then you use a separate camera unit called ICU (ICU = internal camera unit) that comes in different shapes and sizes,
This means that you can customize how you want your backpack to be depending on how much camera equipment versus other equipment you have or want to bring.
I myself have chosen a medium pro ICU (you have to choose "pro" if you want a larger camera body such as the Canon 1D X, or Canon 5D MkIII with a battery grip) because I want to bring other things than just camera gear into the woods/mountains for example.
An ICU has removable inner walls so that you can customize it, like camera bags normally have and are as good as any other that I've tried.
Loka follows international luggage dimensions, but you can easily take out the ICU and bring it into the cabin if you would need to check in your backpack on a flight.
Then there is a long outer compartment for example a jacket or similar, an internal mesh lid pocket and a large outer pocket with compartments and key holders etc.
Later there is a space that is made for a hydration system, such as Osprey or CamelBak, however, you should buy an optional waterproof bag that is hung in this compartment,
which then the reservoir is put inside of (it can fit an Osprey Hydraulics 2L without problems) as additional protection if the container would leak.
A special opening marked H2O where you pull the hose out and attach to the right shoulderstrap through some mesh and a velcro loop.
In addition there are two exterior mesh pockets, one on each side where you can have water bottles or put down tripod feet into.
Compression straps on both sides and also the back, they can be used to attach a tripod and/or skiing/snowboarding/hiking poles/snow shovel or whatever you need.
In a number of places there are loops where you can attach additional straps (called GateKeepers which is optional) if you want to secure a tent/sleeping bag/sleeping pad or similar.
In addition, on both the sides and on the waiste belt, there are anchor points compatible with the MOLLE system (Modular Lightweight Load-carrying Equipment),
which for example the police and military use and there are a plethora of bags and other things that you can attach there if you want.
D-rings are also available to offer yet another way to attach things to the backpack.
Adjustment possibilities are many, and the support system is great and I would think that it fits most people. The good thing with the 3 largest backpacks in the Mountain Series (the ones using ICU's) is that the opening to the camera compartment is towards the back, which means that you can put down the backpack where it is wet or muddy without getting it on the shoulder straps or on the back and if you're in an urban area, your precious camera gear is safe from pickpockets. All zippers are sturdy YKK, some of them are waterproof.
The Loka is meant for day trips, first and foremost, even if you can easily fasten a tent and all kinds of stuff on it, however even with only a medium pro ICU, not a lot of extra space is left in your backpack and especially not enough to take a stove and food for several days of hiking.
If that is what you need, then one should look at the F-stop Satori EXP instead, which I myself will get for next year's hikes and adventures.
Like I said earlier, this backpack is better than anything else I've owned/seen/tried and I could declare that F-stop simply makes THE best camera backpacks available today.
But of course, things could still be improved, and for example the carrying handle that you use to lift the pack with one hand is a bit too thin and could be bigger/thicker.
It doesn't come with a rain cover, though it's probably not very often that you need it, but still. F-stop backpacks are quite expensive, but then again, quality is usually not cheap. And also, it can be quite hard to even get your hands on one. The people at the customer service are friendly, but otherwise the actual service (as in delivering orders to people) needs to be improved.
But as a conclusion, these backpacks (including the Loka) are as good as it gets. If you're a serious shooter, do yourself a favor and get one.
Edit:
I forgot this, so I'll add it here. Thanks to a (very very stupid) corporate decision, F-stop stopped manufacturing the Medium Pro ICU a while ago (I was lucky to get my hands on one), which I see as the ultimate ICU since there's room for quite a lot of gear (I usually have my Canon 5D MkIII w/ battery grip, Canon EF 17-40mm f/4 L, Sigma AF 50mm f/1.4 ART, Tamron SP 24-70mm f/2.8 VC, remote, CF-cards) and still it leaves some space in the Loka for additional gear (since my Lee filters take up a lot of space, I keep them inside of the backpack but outside of the ICU in a Lowepro S&F filter pouch). I forwarded my complains about it to customer support and they told me that other people have done the same, so hopefully they will bring it back.