To get it right, we first need to talk about how a light meter works. Reflective light meters—like the one inside most cameras—assume that the color of any subject you point it at is a middle-toned shade of that color, even if it isn't. If you point it at a red-winged blackbird, it thinks it's a red-winged graybird and it will turn out that way on film. If you point it at a magical white snowscape, it will end up as a dingy, gray landscape. However, you can accurately record these subjects by simply adjusting your camera to let in a little less light for the bird, and a little more light for the snow.

When you use slide film, it's even trickier. Slide film has a hard time recording detail in very light and very dark colors. The black feathers on a red-winged blackbird are about 2 stops darker than middle tone. But, if you adjusted your camera as recommended to let in 2 stops less light, you wouldn't see any detail in the bird's black feathers. Except for the patches of red and yellow, the rest of the bird would appear as a blob of black. Similarly, snow is 2-1/3 stops brighter than middle tone. But, making this adjustment and allowing 2-1/3 stops of additional light to strike the slide film would be disastrous. Just like before, the snow would look like a big blob, but this time it's a white one.

The answer to the black exposure problem is to ease up on your adjustments from one-third to one full stop. For the bird, stop down only one stop, not two. Everything in the picture will be one stop brighter, but the bird will appear perfect with detail in the black feathers. This technique works only if the bird takes up a large percentage of the frame, otherwise, you'll be overexposing the entire scene.

As far as the snowscape goes, it depends if the snow is in the sun. If the snow is sunlit, instead of 2-1/3 stops, open up only 1-2/3 (or 1½) stops. If the snow is in the shade or it's a cloudy day, then open up just 2 stops. This will cause the snow to show detail, but you'll be underexposing the entire scene by 2/3-stop or 1/3-stop, respectively. Therefore, be careful to use this method only when there's enough snow in your picture to require showing detail.

Just imagine a situation where there's a magnificent landscape of wildflowers and a snowcapped mountain in the distance. If the sunny snowcap is small in the frame, it may not be worth underexposing the entire scene. If the snowcap takes up a noticeable, but not overwhelming percentage of the frame, you might want to underexpose by the smallest increment, say 1/3-stop, to keep from blowing out the highlights. If the angle of the sun is right, you may get some benefit from using a polarizing filter to further reduce glare from the shiny snowcap.

As you can now see from the bird and the snow examples, properly exposing slide film is not as simple as black and white. Knowing the exact amount of light falling on the scene is not sufficient. Slide film is not perfect and the meter readings do not tell the entire story.

Though all of this may seem a bit tricky, metering a snow scene is actually extremely reliable and accurate, since the reflectance of snow is fairly predictable. Snow acts as one giant "white card" with a known value of 2-1/3 stops brighter than middle tone. This makes it easy to get an accurate light meter reading simply by spot metering that magical patch of white.

To guarantee the perfect exposure, I often bracket by only the slightest amount— usually only 1/3-stop. For sunlit snow, I open up +1-2/3 and +2 stops. For shady (or "cloudy" snow), I bracket by one-third of a stop around the +2 stop mark. As a result, I often end up with one perfectly exposed picture plus another with a slightly different mood. If your camera only has half stops, bracket around the nearest ½-stop increments. There are really just two steps to perfect snow exposures:

Step 1: Study your snow scene and determine the brightest area of snow that must show detail.

Knowing what to meter is very important, so understand and practice this step. As discussed earlier, there are times when a subject is so small in the frame that recording detail is not necessary. In Example 1, if you decided to record detail in the sunlit accents of snow on the tree branches, most of the snow in the scene will be sorely underexposed. In this case, it is essential to ignore these sunny highlights and expose only for the snow that fills the vast majority of the frame. This is a critical decision that you will need to make.

For snow scenes that are evenly lit (overcast or hazy days, open shade, or full sunlight), pick the snowy spot that seems to be the brightest. In situations where the snow is dappled with sunlight, select the brightest area of sunlit snow.

Step 2: Spot meter the area selected in Step 1 and increase exposure as follows. Sunny Snow: +1-2/3 to +2 stops. Cloudy Snow: +2 stops (bracket if you wish).

In evenly lit situations, this step is a snap. Just spot meter the snow and open up. However, it's sometimes hard to get a spot meter reading from a bright patch of snow in dappled light. If you're using a wide-angle lens, you're spot meter area may record both sunny and shady snow (see Example 2). In this case, fill the spot meter area with a 50/50 mix of sunny and shady. Take the reading and bracket between +1/2 and +1-1/3 stops. This works because the difference between the bright sunny and shady areas is usually not much more than 2 to 3 stops. Another approach is to take an incident light meter reading and stop down between 1/3 and 2/3 of a stop, but you'll also have to factor in light that is lost due to filters and lens extension.

It's a great disappointment to photograph a magical winter landscape, to later find that you're pictures turned out badly. Now, when you find that sensational snowy scene in wondrous winter light, you can concentrate on your creativity and show others how amazing winter really is.