PST (Point Source Transmittance)

PST is a quantitative measure of stray light, defined as the ratio of the light power reaching a detector from an external point source (e.g. the sun) to the power of that source, as a function of the angle between the instrument's axis and the source.

How is PST determined?

PST is determined via simulation (or experimentally), by placing a point light source at successive angles relative to the instrument's axis and measuring the intensity reaching the detector. The result is a PST plot as a function of offset angle from the source — the lower the value, the better the stray light suppression.

Applications

PST is a standard specification requirement for space and astronomical instruments — for example a PST requirement below 10⁻⁴ at a 30° offset from the sun is typical for Earth-observation cameras and telescopes.

Related terms

Stray light

BSDF

Monte Carlo method in optics