Circular Polarising Filter
A rotating filter that blocks polarised light, cutting reflections from non-metallic surfaces and deepening blue skies.
Formula / rule
Effect peak at 90° from the sun
Measured in
stops (EV)
In depth
A polariser is the one filter whose effect genuinely cannot be replicated in software, because it removes light before capture rather than altering pixels afterwards. It costs one to two stops, works most strongly at right angles to the sun, and can darken a wide-angle sky unevenly for exactly that reason. The 'circular' refers to its internal quarter-wave plate, needed so that autofocus and metering still work.
Examples in practice
Rotating a polariser removes the sheen from wet leaves, revealing saturated green instead of white glare.