Walter Graff dispels a commonly held misconception about depth of field in this short essay.

“I can’t tell you how many times I have heard the phrase, if you are shooting an interview and you back up your camera and zoom in your lens putting the person back into frame, you will decrease the depth of field making the background softer. I have heard this from first time movie makers all the way up to very experienced 25 year directors of photography. And there you have one of the greatest myths involving depth of field. It is such a myth that many textbooks print it to this day.”

Graff goes on to explain that what is really happening is a shift in perspective which lends to the illusion of a shallower depth of field. The reality is that the background retains the same amount of out-of-focus blur, but since a longer lens focal length compresses the angle of view, the blurry background objects are larger in the frame, and therefore appear more blurred. Don’t believe me? Go check out the article, there are a few example images that illustrate the point perfectly.