📷 Exposure, Depth of Field & Filter Lab

Four things photographers work out in their heads and get wrong under pressure: what shutter speed balances a change of aperture, how long an ND filter needs, how much of the frame is actually sharp, and whether you can handhold it. All the real maths, no approximations.

Aperture (f/)

Shutter (seconds)

ISO

Focal length (mm)

Focus distance (m)

Sensor

ND filter

A stop is a doubling of light. Aperture stops are √2 apart, which is why the scale runs 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22.

The formulae

Exposure value EV₁₀₀ = log₂(N²/t) + log₂(ISO/100). Anything with the same EV gives the same exposure, so you can trade aperture, shutter and ISO freely.

Depth of field uses the classical thin-lens result with hyperfocal distance H = f²/(N·c) + f, near limit s(H−f)/(H+s−2f), far limit s(H−f)/(H−s−2f). The circle of confusion is taken as the sensor diagonal divided by 1500, which for full frame gives the familiar 0.030 mm. Diffraction becomes visible around f/11 on full frame and much sooner on small sensors, so the sharpest aperture is usually a compromise with depth of field, not the smallest one.