The main body of my insert (i.e., not counting the "peninsula" that holds my GFX 50R) is 24cm wide x 18cm high x 34cm long. An insert that is wider and not as tall would also fit because the bag has no structure when it's empty. If you use a 45 L Atrack, you can make it a few cm taller.
Here it is out of the bag, with a small dog for scale
As you will see, I come from the "ugly but it works" school of design...
Thanks Rob! That is most helpful. Seems like your insert is almost exactly the same depth as the f-stop small ICU (17.8cm). I have it oriented so the long side of it fills the width of the pack (29.2cm). I feel like there is a *little* bit of room to go either deeper or wider but definitely not much. If I want to go deeper (I reckon I will need about 20cm of depth to accommodate my RM3Di) then I am probably better off making my foam block less wide to ensure the zipper will still close.
As for the Atrack mini-review I promised, here it is...
I opted for the loud "Signal Red" version of the Atrack 35 for visibility purposes and it better matched the colour scheme of my other camping gear. It is a bit less subtle than it looks in some of the Ortlieb marketing materials so I may not have picked that colour had I seen it in person, but its main purpose is for camping and hiking so I have no regrets. If I had planned to use it in urban environments I think black would be the better colour choice. I considered getting the 45L version as it comes with good compression straps so you can always make it smaller, however if I have the space I tend to fill it, so I think this will force me to be more economical with my gear.
As Rob mentioned the pack is totally formless on its own, but thanks to the f-stop ICU it can stand on its bottom. Since the pack is totally watertight and airtight, if you close it almost all of the way you can inflate it with your mouth to give it some form before sealing it. I found this handy to give a bit of an air cushion for the gear that didn't fit into the ICU, such as my little point and shoot.
I took the pack with me on a three day canoe trip, and while I thankfully never had to test the Ortlieb waterproof claims, the pack certainly seems well suited to standing up to the elements. I really like the idea of gaining access through the back as I naturally do not put the padded strappy side down when in canoes or on trails as that is where all of the water and mud usually is
. The Atrack quickly gained a home directly in front of my seating position in the canoe so I could get at my camera when necessary.
Inside I currently have an F-Stop small ICU, which is positioned so that the long side goes side to side in the pack. This occupies about 50% of the vertical space in the pack, so there is plenty of space left over currently. This ICU is not deep enough to hold my RM3Di unfortunately. It fits, however one edge of it invariably sticks up out of the ICU, The pack still closes and I tried it this way for a bit, however the edge is far enough out that you definitely can feel it on your lower back, despite it being behind the ample padding of the Atrack.
Pictured here is my Arca Factum, which still sticks out a little bit, however cannot be felt through the padding. I have gone through a few configurations, both with camera disassembled and fully assembled and can safely fit tech cam with 2 lenses, viewfinder, digital back, and basic accessories. When disassembled I can fit more accessories since there is a lot less wasted space. My goal with a custom block of foam will be to fit a tech cam with mounted lens and back, one (or maybe 2?) extra lenses, another back, and basic accessories. Perhaps this is too ambitious, but as you can see there is still a lot of extra room above the ICU so my block will be expanding upwards for sure, but I would like to leave some space to stuff a jacket, lunch, or perhaps my point and shoot.
I also purchased the Ortlieb "Accessory Mounting Kit" along with the pack which comes with a few nifty straps for mounting just about anything you might want to the outside of the pack. There is a smaller strap system meant for hiking poles and the like that I think may be able to carry lighter tripods in side or centre carry positions, but I have not tried it yet. Pictured here is the large accessory mount, which consists of some straps and two "ladder" bits that slide through the mounting holes in various configurations to suit your gear. I have configured mine to carry my RRS 4 Series tripod in the centre, upside down and as low as possible.
Thanks to all of the straps adjustment points I was able to get the legs attached snugly to the pack with minimal play, and certainly no extra sway or movement that could be felt while walking, although with both 4 series legs and Cube attached to the back of the pack, it was getting into less than ideal weight distribution territory. It is just two clips to get the legs attached/unattached, which was done at the beginning/end of each portage. No big deal.
I tried it both with and without the Cube attached, and while it works fine in both configurations I don't want to push my luck with the mount point weight ratings. I also don't have a good protector bag or anything for the Cube just yet so it is rather prone to scuffs, scratches, dings, and dirt whenever setting the pack down since it is the first part of the pack to touch the ground. I have started to use a Phase One lens wrap for it, but still feel better with it off and carried inside the pack. I will probably account for the head in my growing foam block.
Here you can get a sense of how the Atrack with as big a tripod as any of us are likely to hike with sits on my frame. I found the padding and straps to be very comfortable while somehow being minimalist. They were enough to very comfortably carry the weight in the pack for all of my portages, yet never felt like they were in the way at other times. So far a hearty thumbs up for this pack. Thanks to Rob and Mike for bringing it to my attention!