Charles S. Johnson, Jr., is Professor Emeritus at the University of North Carolina at Chapel Hill, NC. Now he is making use of his science background to research and write about the science behind photography. This work attempts to explain light and optics, sensors, and the human visual system. In addition, it provides an introduction to human perception of color, appreciation of art, and cognitive limitations. His leisure activities include travel and nature photography. He is the author of "Science for the Curious Photographer" that was published in 2010 and is available at local booksellers and online.