Abstract: A projection optical system includes a first lens unit adapted to make a enlargement-side imaging surface and an intermediate image conjugate with each other, a second lens unit adapted to make the intermediate image and a reduction-side imaging surface conjugate with each other. The first lens unit has positive power, and the second lens unit has negative power. Defining a focal distance of the first lens unit as fU1, a focal distance of the second lens unit as fU2, a total lens length of the first lens unit as LLU1, and a total lens length of the second lens unit as LLU2, the following expression (1) and expression (2) are satisfied. ?0.3<fU1/fU2<?0.005 ??(1) 0.5<LLU1/LLU2<0.

Abstract: A projection system that can be incorporated in a projector includes a first lens unit that makes a screen (enlargement-side image formation plane), which is located on the enlargement-side, conjugate with an intermediate image and a second lens unit that makes the intermediate image conjugate with a reduction-side image formation plane, which is located on the reduction side. The first lens unit has positive power, and the second lens unit has negative power. A second-lens-unit intermediate-image-side first lens, which is provided in the second lens unit and closest to the intermediate image, has positive power. The following expression is satisfied: ?0.3?fU1/fU2<0 where fU1 denotes the focal length of the first lens unit, and fU2 denotes the focal length of the second lens unit.

Abstract: A projection system includes a first lens group to an n-th lens group with n being 6 or 7 sequentially arranged from a enlargement side. The first lens group includes a first-first lens group and a first-second lens group sequentially arranged from the enlargement side. The two lens groups are separated from each other by a variable distance for image plane correction. The first lens group and the n-th lens group are fixed and the second lens group to the (n?1)-th group are moved when the magnification is changed. The following conditional expression is satisfied: 2<BF/fw<2.8, where fw represents the focal length of the projection system operating at the wide angle end, and BF represents the air conversion length of the back focal distance of the projection system.

Abstract: A projection system includes a first lens group to an n-th lens group with n being 6 or 7 sequentially arranged from a enlargement side. The first lens group includes a first-first lens group and a first-second lens group sequentially arranged from the enlargement side. The two lens groups are separated from each other by a variable distance for image plane correction. The first lens group and the n-th lens group are fixed and the second lens group to the (n?1)-th group are moved when the magnification is changed. The following conditional expression is satisfied: 2<BF/fw<2.8, where fw represents the focal length of the projection system operating at the wide angle end, and BF represents the air conversion length of the back focal distance of the projection system.

Abstract: A projection lens is a zoom lens and formed of a first group to an N-th group sequentially arranged from an image enlargement side (that is, screen side), where N is 6 or 7. The first group includes a first A group and a first B group sequentially arranged from the image enlargement side. The first A group is formed of two positive lenses, and the first B group is formed of a cemented lens formed of a positive lens and a negative lens. The second group includes at least two negative lenses. In magnification changing action, at least the first group and the N-th group are fixed, and at least the third group to the (N?1)-th group are moved along an optical axis. In focusing action, the first A group on the image enlargement side in the first group is solely moved along the optical axis.

Abstract: A projection lens is a zoom lens and formed of a first group to an N-th group sequentially arranged from an image enlargement side (that is, screen side), where N is 6 or 7. The first group includes a first A group and a first B group sequentially arranged from the image enlargement side. The first A group is formed of two positive lenses, and the first B group is formed of a cemented lens formed of a positive lens and a negative lens. The second group includes at least two negative lenses. In magnification changing action, at least the first group and the N-th group are fixed, and at least the third group to the (N?1)-th group are moved along an optical axis. In focusing action, the first A group on the image enlargement side in the first group is solely moved along the optical axis.