Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

To find the center line of the visual field is a very useful concept in photography. Why? It's because a camera is like a gun. And they talk about it that way. People will say that I don't shoot wildlife with a gun; I shoot them with a camera. 

And just as a gun has got a barrel from which a bullet comes out in a straight line, so too is there a straight line from where the photographer is with his camera with its small aperture which is being aimed in a certain direction. THAT DIRECTION CAN BE REPRESENTED BY A LINE.