Nyquist Limit
The highest spatial frequency a sensor can record correctly, equal to half its sampling rate.
Formula / rule
f_Nyquist = 1 / (2 × pixel pitch)
Measured in
lp/mm
In depth
Two samples are needed per cycle to represent it, so a sensor can at best resolve line pairs spaced two pixels apart. Anything finer is aliased into false detail rather than recorded. This is why lens resolution beyond the Nyquist limit contributes nothing useful, and why sensor and lens performance must be considered together.
Examples in practice
A sensor with 4 µm pitch has a Nyquist limit of 125 lp/mm, beyond which finer detail becomes moiré.