Image Clarity 101: Motion blur

In the first and second part of this little series, we have looked at static subjects and a static camera. However, this is not always the case, the subject and the image plane may move relative to one another.

Motion is an issue because the shutter is open for a finite amount of time. And if an image point (we’ll assume, for the time being, that the circle of confusion is small enough to be referred to as a point) moves across the image plane far enough, it will be rendered in multiple pixels (or multiple silver crystals, if you are using film). What was previously a sharp point is now an oval, or even a line.