It was -24 C in Finland during my xmas holiday there but it did not prevent me from photographing. Cold weather like that just requires some preparations. The most important one for your gear is to prevent condensation.
Condensation happens when cold camera is brought indoors. Fog appears on lens surfaces etc and that moist can damage your camera internals as well. Preventing condensation is simple. You need put a camera inside a plastic bag before entering indoors. Wrapping camera inside a bag prevents the warm and moist air reaching the cold surfaces of the camera. Take the wrapped camera indoors and wait half an hour or so to let the camera to warm up.
Cold weather affects camera and accessory batteries as well. In cold they do not hold their charge well and you end up running out of battery sooner. Have an extra battery and store it inside your coat to keep it warm. When the cold camera battery runs out of juice, swap it with the warm one. You should be able to get some extra shots from the empty one after it has warmed up. Do not put the camera inside your coat because of condensation issue.
Especially with older manual lenses the lubrication used in the gears gets stiff in freezing temperatures. There is not much you can do without putting the whole lens apart. Modern lenses use synthetic lubricants and they are not that prone to get stiff. But modern equipment has a lot of plastic parts and some plastics become very brittle in freezing conditions. So be extra careful.
Last but not least is your own body. Keep your fingers and head warm!
