Zoom lens system
AssigneeNittoh Kogaku K.K.
InventorAkira Sawamoto
Life of this patent
Estimating the term…
Abstract
A zoom lens system that includes lens groups G1 to G5 that have negative, positive, positive, negative and positive refractive power respectively in the order from a screen side is provided. The fourth lens group G4 includes a cemented lens made up of a negative lens that is concave on the screen side and a convex lens. The zoom lens system satisfies conditions below 1.15<f2/fw<2.0 50<Δvd4<70 where fw is a combined focal length of the zoom lens system at a wide-angle end, f2 is a combined focal length of the second lens group, and Δvd4 is a difference in the respective Abbe numbers vd of lenses composing the cemented lens in the fourth lens group G4.
Claims6
A zoom lens system that projects, onto a screen, projection light from an image generating device, comprising, in order from a screen side thereof:
- a first lens group with a negative refractive power;
- a second lens group with a positive refractive power;
- a third lens group with a positive refractive power;
- a fourth lens group with a negative refractive power;
- and
- a fifth lens group with a positive refractive power,
- wherein zooming is performed by moving the second, third and fourth lens groups,
- the fourth lens group is composed of a negative meniscus lens that is concave on an image side, a cemented lens made up of a negative lens that is concave on the screen side and a convex lens, and a positive lens, and
- the zoom lens system satisfies conditions below
- 1.15<f2/fw<2.0
- 50<Δvd4<70
- where fw is a combined focal length of the zoom lens system at a wide-angle end, f2 is a combined focal length of the second lens group, and Δvd4 is a difference in respective Abbe numbers vd of lenses composing the cemented lens in the fourth lens group.
Dependencies are inferred from the claim text.