This is a rather well-covered topic, but I will throw in some thoughts nonetheless.
Most articles cover how to take care of your camera, but what is often missing is the significantly more important aspect of clothing. Hence, I will split the article in two parts.
Part I - the camera
It is really surprising to me that some companies advertise their cameras as being “cold-resistant”. Personally, I am entirely clueless as to the meaning of that specification and I have yet to see a clear explanation. As far as I am concerned, I am willing to pay a few bucks for a weather-sealed design, but consider it entirely overrated, as manufacturers simply claim things, but never adhere to any existing standard. Cold, specifically, does not do much to your camera. I have been using Canon, Nikon and Sony models without any weather resistance in temperatures down to -37C during five winters and I have had a real issue only once - the focus ring of a lens getting stuck. Sure, there was the occasional problem with the LCD getting psychedelic colors and plenty of battery drain, but these generally do not stop me from shooting. And all of these issues resolved completely after getting the camera to regular temperatures.
Here are a few rules of thumb that should be observed though.
• Put the camera in a sealed bag before entering your house, so the condensation occurs on the bag and not on your camera.
• Do not exhale onto the camera. Either hold your breath while using the viewfinder or simply use the back screen, while holding the camera at a distance.
• Do not keep the camera close to your body while being outside so as to avoid any moisture. Let it freeze. Do keep the battery warm though.
Part II - the photographer
Speaking from personal experience (what I have done and what I have seen other do), the real issue when shooting in cold weather is that people are badly prepared for the cold. This will necessarily end up ruining any shooting experience, not to mention being actually dangerous. Freezing comes without a warning.
It is really important to be well prepared and know where you are going, for how long, in what environment etc. Some quick tips:
• Use wool. Every year we hear about some new synthetic marvel that finally brings all the qualities of wool, but end up being disappointed after the first serious trials. Things have certainly progressed a lot and there are some amazing materials out there, but just get wool and be done with it.
• Always have two sets of gloves. I have never seen gloves that would both be warm at -20C and below, and yet offer enough dexterity to operate a camera comfortably. Have something comfortable on top of which you can put some mittens.
• I am a big proponent of layering. You can just put a big heavy jacket if you are simply shooting the northern lights and not moving. Otherwise, it is best to layer up, so you can adjust your temperature; you cannot allow yourself to sweat while moving or to freeze while shooting.
• Use all that clothing to your advantage - put things in your pockets to lighten or even leave your backpack at home.