The action of giving something a trapezoidal shape; the result of this. Now chiefly Cinematography, Television, and Photography: the keystone effect; distortion arising from this.
Origin
1920s; earliest use found in U.S. Patents. From keystone + -ing.
Definition of keystoning in US English:
keystoning
nounˈkiːstəʊnɪŋ
The action of giving something a trapezoidal shape; the result of this. Now chiefly Cinematography, Television, and Photography: the keystone effect; distortion arising from this.
Origin
1920s; earliest use found in U.S. Patents. From keystone + -ing.