Zoom lens and image projection apparatus having same

Details Zoom lens and image projection apparatus having same Zoom lens and image projection apparatus having same

2007-05-31

2008-10-07

Spector, David N (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S676000

Reexamination Certificate

active

07433130

ABSTRACT:
A zoom lens telecentric on a reduction side includes a first negative lens, a second negative lens and a first positive lens arranged from the enlargement side to the reduction side. At least one of the first and second negative lenses has an aspherical surface. The zoom lens satisfies −f12/fw<1.4, −f12/(Hwpn−f12)<0.6 and |dn/dt|<1.0×10−5, where f12 is the focal length of the combined optical system composed of the first and second negative lenses, Hwpn is the distance from the rear principal point of the combined optical system composed of the first and second negative lenses to the front principal point of the first positive lens, dn/dt is a change in the refractive index of the material of which said one negative lens is made relative to a change in its temperature from 25° C., and fw is the focal length of the entire lens system at the wide angle end.

REFERENCES:
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patent: 6831706 (2004-12-01), Abe et al.
patent: 6985302 (2006-01-01), Nishida
patent: 7016118 (2006-03-01), Wada
patent: 7289281 (2007-10-01), Sugita
patent: 2003/0234984 (2003-12-01), Nagahara
patent: 2007/0195427 (2007-08-01), Sugita
patent: 2000-275519 (2000-10-01), None
patent: 2004-070306 (2004-03-01), None
patent: 2004-245882 (2004-09-01), None
patent: 2005-062225 (2005-03-01), None

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