Projection lens

A projection lens comprising:

• a first lens group, a diaphragm, and a second lens group, which are disposed in that order from a long conjugate side to a short conjugate side;
• wherein the first lens group comprises a convex-shaped meniscus lens disposed at the long conjugate side and at least one positive lens, so that the first lens group as a whole has a positive refractive power,
• wherein the second lens group comprises at least one set of combined lenses and an aspherical lens, so that the second lens group as a whole has a positive refractive power,
• wherein a gap between predetermined lenses of the first lens group is moved in order to perform a focusing operation, and conditional expressions (5) and (6) are satisfied:
• 1.87 < BF / F Conditional ⁢ ⁢ expression ⁢ ⁢ ( 5 ) 0.22 < HF2 / F2 < 0.57 Conditional ⁢ ⁢ expression ⁢ ⁢ ( 6 )
• where F denotes a focal length of the projection lens, BF denotes a distance in air from a last lens surface of the second lens group to a small conjugate point when a projection magnification is a predetermined value, F2 denotes a focal length of the second lens group, and HF2 denotes a location of a front principal point of the second lens group.

A projection lens comprising:

• a first lens group, a diaphragm, and a second lens group, which are disposed in that order from a long conjugate side to a short conjugate side,
• wherein the first lens group comprises two lens subgroups comprising two lenses, an aspherical lens disposed at the long conjugate side, and a positive lens, so that the first lens group as a whole has a positive refractive power,
• wherein the second lens group comprises two lens subgroups comprising three lenses, a set of combined lenses and an aspherical lens, so that the second lens group as a whole has a positive refractive power,
• wherein a gap between predetermined lenses in the first lens group is moved in order to perform a focusing operation, and conditional expressions (10) and (11) are satisfied:
• 1.87 < BF / F Conditional ⁢ ⁢ expression ⁢ ⁢ ( 10 ) 0.22 < HF2 / F2 < 0.57 Conditional ⁢ ⁢ expression ⁢ ⁢ ( 11 )
• where F denotes a focal length of the projection lens, BF denotes a distance in air from a last lens surface of the second lens group to a small conjugate point when a projection magnification is a predetermined value, F2 denotes a focal length of the second lens group, and HF2 denotes a location of a front principal point of the second lens group.

A projection lens comprising:

• a first lens group, a diaphragm, and a second lens group, which are disposed in that order from a long conjugate side to a short conjugate side,
• wherein the first lens group comprises two lens subgroups comprising two lenses, an aspherical lens disposed at the long conjugate side, and a positive lens, so that the first lens group as a whole has a positive refractive power,
• wherein the second lens group comprises either two lens subgroups or three lens subgroups, the two lens subgroups comprising three lenses, an aspherical lens disposed closest to the diaphragm, and combined lenses, and the three lens subgroups comprising four lenses, an aspherical lens disposed closest to the diaphragm, a positive lens, and combined lenses, so that the second lens group as a whole has a positive refractive power,
• wherein a gap between predetermined lenses in the first lens group is moved to perform a focusing operation, and conditional expressions (15) and (16) are satisfied:
• 1.87 < BF / F Conditional ⁢ ⁢ expression ⁢ ⁢ ( 15 ) 0.22 < HF2 / F2 < 0.57 Conditional ⁢ ⁢ expression ⁢ ⁢ ( 16 )
• where F denotes a focal distance of the projection lens, BF denotes a distance in air from a last lens surface of the second lens group to a small conjugate point when a projection magnification is a predetermined value, F2 is a focal length of the second lens group, and HF2 is a location of a front focal point of the second lens group.

A projection lens comprising:

• a first lens group, a diaphragm, and a second lens group, which are disposed in that order from a long conjugate side to a short conjugate side,
• wherein the first lens group comprises either two lens subgroups or three lens subgroups, the two lens subgroups comprising two lenses, an aspherical lens disposed at the long conjugate side and a positive lens, and the three lens subgroups comprising three lenses, an aspherical lens disposed at the long conjugate side, a negative meniscus lens, and a positive lens, so that the first lens group as a whole has a positive refractive power,
• wherein the second lens group comprises two lens subgroups including three lenses, a set of combined lenses and an aspherical lens disposed at a short conjugate side, so that the second lens group has as a whole a positive refractive power,
• wherein a gap between predetermined lenses in the first lens group is moved to perform a focusing operation, and conditional expressions (20) and (21) are satisfied:
• 1.87 < BF / F Conditional ⁢ ⁢ expression ⁢ ⁢ ( 20 ) 0.22 < HF2 / F2 < 0.57 Conditional ⁢ ⁢ expression ⁢ ⁢ ( 21 )
• where F is a focal length of the projection lens, BF is a distance in air from a last lens surface of the second lens group to a small conjugate point when a projection magnification is a predetermined value, F2 is a focal length of the second lens group, and HF2 is a location of a front principal point of the second lens group.