Aperture Blades
The overlapping leaves inside a lens that form the iris, whose number and shape determine the geometry of the opening.
Measured in
count
In depth
More blades produce a rounder opening when stopped down, which keeps out-of-focus highlights circular rather than polygonal. Rounded blade edges achieve the same at lower cost. The blade count also determines sunstars: an even number of blades produces that many rays, an odd number produces twice as many.
Examples in practice
A nine-bladed lens renders an eighteen-point sunstar at f/16, while a seven-bladed one gives fourteen points.