The Alta mitt is just not functional when at field photographing, If you ware it, you can't open the zipper from one hand to another due to the tactless. It is easier if you take your hands out of the mittens, then open the zipper, or just keep using the hands "free". From -20ºc to -41ºc, I can say that it is impossible, to do anything with the camera, is really just to use it when not needed to operate the camera, and again, you need to take it out. Too expensive to not have a giant YKK zipper or so.