Patent ID: 6590716
Filing Date: 2003-07-08
Classification: G02B

Abstract:
A projection zoom lens comprising a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power;wherein the first, the second, the third and the fourth lens groups are arranged in that order from a screen side toward an image plane side along an optical axis; the first and the fourth lens groups are kept stationary, and the second and the third lens groups are moved along the optical axis to vary power from a limit wide angle power toward a limit telephoto power; the second lens group includes a 2nd-group 1st positive lens, a 2nd-group 1st compound lens formed by joining a 2nd-group 2nd positive lens having a convex surface on the image plane side and a 2nd-group 1st negative lens having a concave surface on the screen side, and a 2nd-group 3rd positive lens arranged in that order from the screen side toward the image plane side; the third lens group includes a 3rd-group 1st meniscus lens having a concave surface on the image plane, a 3rd-group 1st compound lens formed by joining a 3rd-group 1st negative lens having opposite concave surfaces and a 3rd-group 1st positive lens having opposite convex surfaces, and a 3rd-group 2nd meniscus lens having a convex surface on the image plane side arranged in that order from the screen side toward the image plane side; the first lens group has a focal length f1, the 2nd-group 1st positive lens and the 2nd-group 1st compound lens have a composite focal length f2AB of a sign opposite to that of the focal length f1, and the focal length f1 and the composite focal length f2AB meet an inequality: 0.51/f2AB|<2.0.