Just about all equipment is rated for use down to 0°C. However at lower temperatures there are a few things that may cause problems.

Most cold weather work will probably be done in the range from freezing down to -18°C, since not too many places get much colder than that for more than a few days a year. However there are places that get down to -40°C. If it goes below -40 degrees, it's a serious reason to think about staying indoors with a glass of tea or Gluhwein. Note also that "wind chill" factors don't apply to cameras, only to people.

Digital cameras are specified by their manufacturer only for operation down to a temperature of 0°C, as a rule they will work well at lower temperatures, but they aren't rated for lower temperature work because they aren't tested to fully meet all specifications at those temperatures and because there are some problems that can happen below zero. However most of these can be avoided. Besides which, electronic components work better at lower temperatures, so there's really no issue with the electronic circuitry.

The problems which may arise in very cold weather are usually either mechanical, related to LCD displays or related to battery issues. At just what temperature problems occur depends on the exact design of the equipment, but most modern cameras and lenses are just fine at -20°C and can even be used down to -40°C with some care and attention.

Plastics
At very low temperatures plastics may become quite brittle and will break before they bend. This means you need to be careful when opening any plastic camera doors (for example: battery compartment doors) to avoid accidental damage.

Snowy Afternoon (C) Natalia Sanina, 2007, all rights reserved Canon 20D

Memory Cards
There are very few reports of memory cards having problems at low temperatures. Indeed, there are no moving parts that can be damaged or broken, and for the chip inside frost doesn't matter at all. The Sandisk Extreme cards are specified for use down to -25°C but even they are probably not required. Most users seem to find that even at the lowest temperatures their memory cards perform without problems.

Some problems may occur with microdrives because they are mechanical devices. But this media is not very popular at the moment.

The Displays
The Liquid Crystal Displays (LCD) are affected by low temperatures. They may lose contrast (grey out), change the displayed information more slowly, may change color. No panic - once they warm up, all properties should be back again.


Attention! Metal
Touching metal parts at temperatures below -10°C with your bare hands can be quite a painful experience. Moisture on your hands can freeze and "glue" you to the metal surface! Digital cameras are made from plastic or at least have a plastic cover, therefore there's no problem when handing them, but touching bare metal tripod legs with ungloved hands... You can get insulating sleeves for tripod legs (or you can use pipe insulation) or even a carbon-fiber tripod (but it is not the cheapest piece of kit on the market).

Power Supply
Batteries lose a lot of their power at low temperatures. This applies to absolutely all battery types but some do better in low temperatures than others. The best cold performance probably comes from non-rechargeable Lithium cells, followed by NiCd, NiMH and Li-ion rechargables. If they get really cold and become exhausted they will regain power if warmed back up. Taking 2 or 3 (if not more) battery sets out in the field with you and switching them from your camera to a warm pocket and back should solve this problem.

For some camera systems an external battery pack is available which connects to the camera via a cable. You can keep the batteries warm under your clothes, but the cable between the battery pack and the camera can be inconvenient.

Exposure
The influence of low temperature on a measurement sensor is insignificant, but when shooting with snow around exposure correction is required. As a rule snow landscapes need +1...+2 eV correction. Some cameras with multipoint metering systems are able to calculate the exposure correctly and need lower correction or no correction at all.

Lens protection
In the bleak midwinter when snow is falling or blowing it is important to protect the front element of your lens with a UV (or Skylight) filter. These are a useful additional shield against moisture and, especially in sunny weather against UV rays. The Skylight's warming effect is also not a bad idea.

Coming in from the cold
A major problem can occur not while you are outside, but when you come back into a warm area. Very cold air is very dry, but air in a heated room usually contains moisture. When you bring very cold equipment into a room with warm, moist air, moisture will condense out of the air onto the cold surfaces. The main problem is the moisture which condenses on internal parts. Electronics don't like moisture and condensation on the internal elements of lenses is really unwanted too.

After warming the equipment, the moisture will evaporate, but it takes time. Be warned! Forcing this process with a hair dryer is not a good idea.

To avoid problems with condensation inside a camera, remove the batteries and don't insert them until you are sure the camera has dried out. Just because a camera is "off" doesn't mean that electronics are safe from damage. Some cameras are just in a "sleep" state when off, with power still applied to some components.

You can avoid these problems if you seal your camera gear in an airtight plastic bag before(!!!) you bring it inside. It will then be surrounded only by the very dry air from outdoors. You may get some water on the outside of the bag, but the camera/lens will slowly warm up in dry air inside the bag and will stay dry. Just be sure to put the camera/lens in the bag before you go indoors.