The Exposure Triangle; you’ve heard of it, I’m sure. It’s fabled in story and song and celebrated by photo instructors everywhere. We can even buy t-shirts commemorating the concept! There have been countless articles written about the “exposure triangle” (try a web search and see for yourself), all with the intent of helping newcomers to photography figure out how exposure works in their cameras.
Some of these articles are obscure and pedantic and, as my friend Shaw would put it, indulge in technobabble to impress the reader with the writer’s expertise. Others make a sincere effort to communicate important information to the reader, but all of them fail to acknowledge that beyond ISO, aperture and shutter speed, there is a fourth part of the exposure equation, the part without which there would be no exposure at all; and that part is light.