Exposure — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
Also named here as hyperfocal distance — the same set of essays touches all of them, so they are one junction rather than several.
The sharp band is a decision
One 50 mm lens at f/2.8 focused at three metres has a sharp band half a metre deep or an unbounded one, and nothing about the optics changes between them — only how large a blur disc a reader is prepared to ignore. Every quantity usually quoted about depth of field is that acceptance restated, including the rule that a third of the band lies in front, which is true at one distance and nowhere else.
The disc and the streak
A frame integrates over the pupil and over the exposure at once. Hold the point's depth and the patch is exactly the streak of its centres with one disc slid along it, to 1.8 × 10⁻⁵ of its own width. Let it recede over the same exposure and the disc's radius falls by 3.7 along the streak, and the patch departs from any single kernel by 16 pixels.
Named alongside it
The objects these essays reach for when they reach for this one.
ApertureCircle of confusiondepth of fieldEntrance pupilHyperfocal distanceinstrument limitSensorConvolutionFocal lengthFree parameterMotion blurPoint spread function