Preshoot white balance and metering

Obviously, if you're shooting a winter landscape, you're very likely going to encounter snow. In addition to making your feet very cold, it's possibly going to confuse the light meter in your camera. Your light meter assumes when you point it at something, that you're pointing it at something that is 18% gray. It then calculates a shutter speed and aperture and possibly an ISO. That will represent what ever it is you're pointed at as 18% gray. It does this calculation because it turns out that most scenes in the world reflect 18% of the light that strikes them. So an assumption of 18% gray leads to good exposure. Whoa! Here when I'm pointing at a field of white I'm not pointed at 18% gray. My camera might still give me a set of exposure values to represent it as 18% gray. The practical upshot being my snow is going to come out looking gray. Now in the old days, in early light meters. You always had to overexpose, because the meter would absolutely always decide that snow needed to be gray, and so you would need to dial in some overexposure to brighten that gray snow back up into accurate white snow. Today's meters are much more sophisticated. They can often figure out that you're shooting at snow. Or, your camera might have a special sand and snow mode, which will help improve the tonal rendering of snow. You need to just experiment with your camera a little bit. When you first get to a snowy environment, take a shot, look at the histograms, see if you got pure white. If not, then you know you need to overexpose. It may not need to be very much, it might only be 1 3rd of a stop, it may need to be a whole stop. But this is something you need to figure out before you go out shooting. If you leave your meter as is and go out, you may find out that a lot of your snow images come back with the snow as middle gray. Now you can brighten that up in post, but if you do that, you're going to use up a lot of the edit ability of the image. You will have already done a very large edit just to get white back to where it needs to be. If you want to push further edits into that picture. You're possibly going to start seeing tone breaks and posterizing. Something else that might happen. The sun has now set, and so now I've lost this nice white snow that I had before, and I'm into a shady situation. I need to think about white balance. There are two things that are going to affect what my snow looks like. Exposure, which is going to control the tonality and white balance, which is going to control the color. I almost always shoot an auto white balance because I pretty much always shoot raw, so I can change my white balance after the fact. However, auto white balance on all of my cameras, especially my Canon cameras, always fails a little bit. Well not fails, it doesn't do as good a job when shooting in shade like this. So snow that to my eye maybe looks white, is going to come out looking very for want of a better word cold in shade with auto white balance. So I need to get in the habit of either manually white balance, switching to my camera's shady white balance. Or simply understanding that I'm going to need a lot of white balance adjustment when I get back into post production. Now, these are two things that you need to think about in any scene, exposure and white balance. But with snow you really need to learn your camera's characteristics for shade, for sun, white balance to know if you are going to get a color cast on your snow. And for how it meters snow, to figure out if you're going to need a little bit of extra exposure compensation. Simple test to do as soon as you get into a snowy environment. Once you've figured that out, you're fine for the rest of your shoot.