Visual Plane
every picture states the point it is correct from
Concept

Hyperfocal distance — where it appears

The focus setting whose far limit of acceptable sharpness is infinity. Focused there, everything from half of it outward is inside the band, and it is the single number the whole depth-of-field arithmetic follows from once a criterion is chosen.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

00.50011.50-0.25000.2500.5000.750the blur a reader is prepared to call sharp, in pixels (powers of ten)near and far limits of the band, in metres (powers of ten)the focus distance2 pxone lens, one focus setting, five criteria5 bands

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.

sensor · Aperture at one depth — a stadium, to 1.8e-5receding — tapered, 4% outone point, one exposure, the whole pupil1.8e-5 against 4%

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.

sensor · Aperture

Named alongside it

The objects these essays reach for when they reach for this one.

ApertureCircle of confusiondepth of fieldEntrance pupilExposureinstrument limitSensorConvolutionFocal lengthFree parameterMotion blurPoint spread function

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