Nittoh Kogaku K.k.

Akira Sawamoto

Shuji Narimatsu

A zoom lens system that has two lens groups with respectively negative and positive refractive powers in that order from a display medium, such as a screen, side is provided. The first lens group and the second lens group respectively include at least one aspherical surface. An air distance dw between the first lens group and the second lens group at the wide angle end, an air distance dt between the first lens group and the second lens group at the telephoto end, a combined focal length fof the first lens group, a combined focal length fof the second lens group, and the combined focal length fw of the zoom lens system at the wide angle end satisfy the following conditions: 0.05&#x3c;dt/dw&#x3c;0.1; dt&#x3c;2.5 mm; 1.3&#x3c;|f/fw|&#x3c;1.6; 1.1&#x3c;|f/f|&#x3c;1.4.

Zoom lens system and display apparatus

A projection zoom lens that is suited to projector with a DMD is provided. The projection zoom lens projects, onto a screen, projection light from the DMD and comprises, in order from a screen side, a first lens group with negative refractive power and a second lens group with positive refractive power. The second lens group includes, from the DMD side, a final lens that is a positive lens, a pre-final lens that is a negative biconcave lens positioned next to the final lens, and a stop, and both surfaces of the pre-final lens are aspherical. Using the projection zoom lens, it is possible to realize the compact projector that can project bright images with high resolution that makes full use of the characteristics of the DMD.

Projection zoom lens and projector

A zoom lens system that includes lens groups Gto Gthat have negative, positive, positive, negative and positive refractive power respectively in the order from a screen side is provided. The fourth lens group Gincludes 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 below1.152&#x3c;2.0504&#x3c;70 where fw is a combined focal length of the zoom lens system at a wide-angle end, fis a combined focal length of the second lens group, and &#x394;vdis a difference in the respective Abbe numbers vd of lenses composing the cemented lens in the fourth lens group G

Zoom lens system

A projection zoom lens system according to the present invention has a substantially telecentric incidence side and comprises a plurality of lens groups for behaving differently between a wide-angle end and a telephoto end, wherein at least one of two surfaces of a lens included in a first lens group located closest to a screen side has an aspheric surface. Since the lens closest to the screen has the largest diameter and the density of light rays becomes smallest among the lenses, it is possible to design the aspheric surface for correcting properly the light rays and reduce the correcting loads of the other lens groups constituting the projection zoom lens system so as to provide the compact and high performance zoom lens system.

Growing community of inventors

Suwa, Japan

Akira Sawamoto