Patent ID: 8147096

Claim:
A zoom device for a lighting fixture, comprising: a first lens assembly ( 13 ) of positive refractive power; a second lens assembly ( 14 ) of negative refractive power; and a third lens assembly ( 15 ) of positive refractive power; the first lens assembly ( 13 ), second lens assembly ( 14 ), and third lens assembly ( 15 ) being aligned along a longitudinal axis (A) coincident with the axis of a light beam emitted by a light source ( 3 ) of the lighting fixture ( 1 ); the third lens assembly ( 15 ) being located close to the light source ( 3 ) of the lighting fixture ( 1 ), and the second lens assembly ( 14 ) being located between the first lens assembly ( 13 ) and the third lens assembly ( 15 ); the zoom device ( 10 ) being characterized by satisfying the following conditions: 2.12 < F 1 F m < 2.80 ⁢ - 0.55 < F 2 F m < - 0.81 0.6 < F 3 F m < 0.84 F m = ( F s · F l ) 0 , 5 where: F s is the focal length of the zoom device ( 10 ) when the second lens assembly ( 14 ) is in a wide-angle position; F 1 is the focal length of the zoom device ( 10 ) when the second lens assembly ( 14 ) is in a narrow-angle position; F 1 is the focal length of the first lens assembly ( 13 ); F 2 is the focal length of the second lens assembly ( 14 ); F 3 is the focal length of the third lens assembly ( 15 ).