ONE OF THE HUGELY OVERLOOKED custom functions of the higher-end DSLR cameras is the ability to quickly and seamlessly make double exposures. Hell, the camera even figures out the gain for you. In the old days, it was pure guesswork when you re-exposed a piece of film. Go a half stop under for the second exposure? Full stop? Pure seat-of-the-pants, hope-for-the-best, Hail Mary stuff. Now, the camera thinks it through for you.