Have you heard the one about how you have to overexposed your images when shooting in snow? Does that sound counter intuitive to you? After all with all that white ‘n’ light about surely you have to underexpose right?
To understand why you have to overexpose requires understanding something of the basics of how a camera light meter “reads” a scene. Now this applies whether you have a brand new, state-of-the-art DSLR or your using grandpa’s old Nikon FM (old fogies start sighing here!).
That basic principle that your camera is following is the principle that the scene it’s looking at is “18% gray”. The camera is assuming that mostly everything contained in your scene is has a luminance of 18% (this is subtly different to reflectance but I won’t go into that in this post).
What this means to you is that when your scene contains a lot of bright white “stuff”, like snow or, ummm a wedding dress, your camera is going to try to “assume” that it is really 18% gray and UNDER expose! Your snow will look gray and yucky and somewhere around here your bride and her mother will be chasing you with heavy sharp objects.
Remember, if you are shooting something that is really white, expect to need to use your exposure compensation to ‘bump’ up your exposure anything from 1/3 to a full stop.
The image above was shot on my iPhone and I am fairly impressed that it did a pretty good job of my snow covered car from this weekend in Prescott, AZ. I feel that it is a touch underexposed though.