Yesterday I was out in -30C (-22F) for several hours shooting with my Linhof Techno and Leaf Aptus 75.
I've had lots of troubles with reliability in colder temperatures in the past with the Aptus until I got it replaced (under warranty) some months ago. As I've had troubles I had not really tested to shoot with the system in colder temperatures than -15C (+5F) before, so this was a first.
I'd say that down to -15C (+5F) the mechanical properties are close to the same as in room temperature. Drop down to -30C and you are in for some challenges.
Oil gets stiff in cold temperatures, so some gears get tougher to work with. The top and bottom pano of my Arca-Swiss D4 head got significantly stiffer (the gears not so), but not so it became hard to operate. The Techno's focusing mechanism has a friction adjustment, by releasing that to a minimum focusing has about the same tactile feel as in warmer temperatures. The tilt gear becomes so stiff that it's really tough to move, but not impossible. I did not try the swing though, I suspect that it would be near-impossible to operate though (as it's quite stiff also in room temperature and the knob is small), fortunately I don't use swing too often. Vertical shift also require some significant effort, but it's okay as long as you're not in a hurry. Shifting 10mm takes more than a few seconds. I noticed swirls in the fluid of the Techno's bubble levels, they reacted a bit slower but did not freeze.
The Schneider Digitar plastic push-on lens caps shrink in cold temperatures, some got really tough to remove from the lens. I've replaced most lens caps with regular spring-loaded ones (recommended). I think it's a bit sloppy by Schneider not using more temperature-stable plastic in their caps (this is supposed to be high-end gear!), I've noted that some can get overly loose if the weather is warm too.
I have short cable releases attached to each lens so I don't need to detach and re-attach it all the time, which you don't really want to do in -30C. I have a pair of leather mittens on my hands, which stop wind and are more sweat resistant and much warmer than gloves, and you can do surprisingly much with the camera with them still on. I use my bare hands for changing aperture on the copal shutter, holding my tiny loupe when focusing, but the rest I do with the mittens on. I will probably look for an inner glove though, with some grippy surface to keep maximum dexterity (I have some wool liners but they're too slippery). The main problem with bare hands (except instant freezing if windy condition, it was no wind in this case) is that contact with -30C metal is very painful, and practically all parts of the camera is metal. If you happen to touch it it's so cold that it's more of a burning sensation than cold. A thin rubber coating on all metal parts would have been nice :-).
I also have to hold my breath when focusing, or else the breath will fog my glasses and/or the loupe and ground glass. In these cold conditions I don't really bring out my DoF tables and think much about optimizing, I focus as quickly as possible and base aperture etc on estimates and experience. In all one tries to work faster than in more comfortable weather. Due to this it's more likely I shoot HDR series than bring out the graduated filters as I would in warmer weather, to speed up workflow.
The digital back worked without any issues at all, a huge difference compared to prior the replacement when I could have random failures from +10C and lower (+50F). I detached the battery and kept it in my pocket and attached it when shooting. The external battery compartment of the Aptus worked really well for this, easy to access. The LCD screen got a bit sluggish, as cold LCD screens get, but that's the only thing that made a difference (oh well, less noise in longer exposures too of course, a bit unfortunate that the firmware has a hard limit at 30 seconds, in this temperature I'm sure it could be substantially longer).
Anyway, from this experience I think it's surely possible to shoot with the tech cam in -30C, a bit harder to operate but not over the limit. Here in northern Sweden -30C limit means you can shoot even the coldest days most years (-42C is the coldest I've experienced in my life so far).
Note that with wind it will become a much more difficult situation though as it's much harder to keep warm through the workflow, but then I probably stay indoor. The real beauty of cold weather is when it's still and crisp.
Concerning condensation, tricks with plastic bags that you read about is not really necessary. What you do is that you keep the gear in the backpack for a while so temperature lowers slowly. When I've shot the last image I remove the CF card outside so I can start processing images as soon as I get in, but then leave the gear in the closed backpack for a few hours so it warms up slowly.
The attached image was shot yesterday in -30C, Linhof Techno, Schneider Digitar 72/5.6 at f/11, Leaf Aptus 75, LCC-corrected and lightly tonemapped with Lumariver HDR to control the bright highlight of the tree, and then converted in RawTherapee. White balance with snow in shadow mixed with snow lit with a low sun is really difficult. I have set the white balance to make the sun-bathed tree look right, and then reduced saturation of blue to make the snow in shadow look reasonable. I generally choose to keep some blue cast of the snow though to make it look colder. The eye also experience it as a little blue in these conditions, but not fully as much as in my interpretation.
