Birch, Stewart, Kolasch & Birch, LLP
Projection type zoom lens and projection type display apparatus
Disposed in order from a magnification side are a negative first group which is fixed during zooming to effect focusing, second to fifth groups of positive refractive power which move with mutual relationship during magnification variation, and a fixed sixth group. A negative lens made of a glass material which has an anomalous dispersion property and which has 70 or more in Abbe number is disposed in the first lens group. A positive lens made of a glass material which has an anomalous dispersion property and which has 70 or more in Abbe number is disposed in the third group located closer to a reduction side than a diaphragm. The negative lens and the positive lens are cemented to their adjacent lenses, respectively. Also, bf/fw ≧2.7 is satisfied where bf denotes a back focus, and fw denotes a focal length of the entire system at a wide-angle end.
Fujinon Corporation
G
G02B
inventional
Hiroshi
Yamada