Lens speed / Fast lens
Lichtsterkte · Lens & optics
The maximum aperture of a lens; a fast lens has a wide aperture that lets in a lot of light.
A lens with f/1.4 or f/1.8 is "fast" and performs well in low light while giving shallow depth of field. An f/5.6 lens is "slow". Fast lenses are heavier and more expensive but give more creative control and better performance in the dark.
Tools that help with this: