Circle of confusion

[davide sorasio]

Hello everybody, can anybody tell me what circle of confusion is? I've looked for explanations but I could not find one that is easily understandable.

Thanks in advance,

 

Davide

[dan kessler]

We tend to talk about lens properties such as focal length and image plane in absolute terms. We visualize a cone of light from a lens coming into focus at an exact point. Ideally, the film or sensor is positioned at that point, rendering the sharpest possible image. However, there is a margin of error, a deviation from that exact point, that our eyes will allow, yet still perceive as sharp. The light cone can overshoot or undershoot the plane of exact focus, producing circles, rather than points. The maximum allowable circle size that we still perceive as sharp is called the circle of confusion.

It is this concept that gives us depth of field, or a range of perceived sharpness, rather than just a single plane.

For 35mm motion picture film, I think the maximum allowable circle size is approximately .001 inch.

Edited June 6, 2015 by dan kessler

[davide sorasio]

Thank so much! this is really clear!

[Bill DiPietra]

If you eventually want to get into the complexities of all of this, you can pick up a copy of Optics & Focus for Camera Assistants. This and much more is explained in the very first chapter, so you can imagine how much information is in the entire book!