Here's one. When photographing one evening in Tennessee many years ago the exposure was long becasue the light was failing. When the 10 minutes I had calculated were up I added another 10 and then yet 7 or 8--the light was fading very fast. Exposure over, I removed the lens from the camera, put it in my lens bag and only then realized that I had forgotten to put the dark slide back in.
Michael A. Smith