An overall exposure of this scene would have caused the image to be very underexposed. By opening up the aperture, or overexposing from what the light meter indicates, allows the scene to be "properly" exposed. (Photo by Peter Power/The Globe and Mail)pmpPeter Power/The Globe and Mail
Photographs in a cold and snowy environment can certainly be stunning, but also provide a new set of challenges for photographers and their equipment.
When temperatures dip below freezing, it is important to keep yourself warm, first and foremost. Most professionals I know carry quite an assortment of warm, protective clothing close at hand so it is there when you need it. If you know you are going to be shooting in the cold, plan ahead. Dressing in layers is very important, and consider carefully what you wear on your hands. A thin inner layer is a good idea and there are some you can buy that have "grippy" palms. You'll find this important if you want to make some camera adjustments but do not want to expose your bare skin for any length of time.
Most cameras in wide use today depend heavily on their electronics, so keeping your batteries charged and working is next on the list. While different types of batteries tend to have different performance levels in the cold, it would be wise to ensure that you have at least one spare battery with you that you can keep warm. If you have several camera batteries on hand you can rotate through them through the camera, keeping them inside your coat when not being used. The cold will reduce a battery's performance so by switching to a warm battery from time to time you will increase your shooting time. Keep you charger in your room, and try to begin your day with fully charged batteries.
The other danger to be aware of when working in a cold environment is that of condensation on and/or inside your camera and lenses. It isn't uncommon for professionals covering a Grey Cup game in sub-zero temperatures for example, to keep one or two cameras inside, in the warm, to use during post-game celebrations, rather than deal with the condensation and fogged lenses caused when bringing the cameras inside from the cold.
Having spare cameras isn't an option for the majority of photographers, and unless time is an issue, really isn't necessary. The best way to avoid condensation on your lenses and cameras is to place your cameras and lenses in a sealed plastic bag before bringing them inside. Large ziplock bags work well, but anything you can seal airtight will work. Once inside the condensation will form on the outside of the bags, which can be removed once your cameras have warmed up. Also, the exterior of your cameras will warm up sooner that the inside, so it is also an idea to delay changing lenses until more time has passed. Condensation inside the camera and/or on the rear lens element will result if you do not wait long enough.
Exposing your images with the abundance of white snow and ice is the next challenge for photographers. If you trust your camera's exposure meters to do the work for you the meter will tend to be fooled by the abundance of bright light, and your scenes will tend to be underexposed as a result. This is obvious when the snow appears grey in your photographs. It is best in bright, snowy situations to meter manually using one of variety of methods.
A general rule of thumb is that snowy scenes you need to overexpose the average light reading by at least one stop, and often two. With digital cameras it is fairly easy to adjust your exposure compensation to +1, and see how the images look you're your camera will show a histogram - a graphical representation of the tones throughout your image - you can use it to ensure that the highlights are not completely washed out.
With that said, the most reliable way to meter a scene is to measure your exposure off of something of a neutral tone. An 18% grey card, sold in many camera stores, is one option, but it also possible to get an accurate exposure reading from a portion of a clear blue sky. You can also meter off of the palm of your own bare hand, held close enough to your lens that it covers most of the scene. Always ensure that the light you are measuring in the foreground is of the same intensity as that which is lighting your scene.
The last thing to mention is what to do if you get snow on your camera and or lens. Since the snow is cold, it will not melt on your lens. Do not try to blow it off as this will melt some of it and you'll create more of a mess than you started with. Simply brush away as much snow as can.
As with many of the answers and questions we are sure to share here, there are many, many variables that will contribute to your final results. Personally I always try to underexpose my snow scenes just enough to keep detail in the snow. Getting rid of overexposed highlights in your images after the fact is difficult, and best avoided.
Click here for more on Peter Power and a gallery of his work.