Variable magnification optical system for projection and projection-type display apparatus

A variable magnification optical system for projection comprising:

• a first lens group having negative refractive power, and which is fixed when magnification of the variable magnification optical system is changed;
• a second lens group having negative refractive power, and which moves when magnification of the variable magnification optical system is changed;
• a third lens group having positive refractive power, and which moves when magnification of the variable magnification optical system is changed;
• and
• a fourth lens group having positive refractive power, and which is fixed when magnification of the variable magnification optical system is changed, the first lens group, the second lens group, the third lens group and the fourth lens group being arranged from the magnification side of the variable magnification optical system in the order mentioned above,
• wherein the reduction side of the variable magnification optical system is telecentric, and
• wherein the following formula (12) is satisfied:
• −10.0<f1/fw<0.0 (12),
• where
• f1:
• focal length of the first lens group, and
• fw:
• focal length of entire system at wide angle end.

A variable magnification optical system for projection comprising:

• a first lens group having negative refractive power, and which is arranged on the most magnification side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• a final lens group having positive refractive power, and which is arranged on the most reduction side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• and
• a plurality of lens groups that are arranged between the first lens group and the final lens group, and which move when magnification of the variable magnification optical system is changed,
• wherein a most-magnification-side lens group among the plurality of lens groups that move when magnification of the variable magnification optical system is changed has negative refractive power, and
• wherein a most-reduction-side lens group among the plurality of lens groups that move when magnification of the variable magnification optical system is changed has positive refractive power, and
• wherein the reduction side of the variable magnification optical system is telecentric, and
• wherein the following formulas (11) and (12′) are satisfied:
• 1.5<Bf/fw (11);
• and
• −10.0<f1/fw<−2.0 (12′),
• where
• Bf:
• back focus in air of entire system at wide angle end,
• fw:
• focal length of entire system at wide angle end, and
• f1:
• focal length of the first lens group.

A variable magnification optical system for projection comprising:

• a first lens group having negative refractive power, and which is arranged on the most magnification side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• a final lens group having positive refractive power, and which is arranged on the most reduction side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• and
• a plurality of lens groups that are arranged between the first lens group and the final lens group, and which move when magnification of the variable magnification optical system is changed,
• wherein a most-magnification-side lens group among the plurality of lens groups that move when magnification of the variable magnification optical system is changed has negative refractive power, and
• wherein a most-reduction-side lens group among the plurality of lens groups that move when magnification of the variable magnification optical system is changed has positive refractive power, and
• wherein the reduction side of the variable magnification optical system is telecentric, and
• wherein a stop is arranged in the final lens group, thereby setting the numerical aperture of the variable magnification optical system constant through the entire range of variable magnification.

A variable magnification optical system for projection comprising:

• a first lens group having negative refractive power, and which is arranged on the most magnification side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• a final lens group having positive refractive power, and which is arranged on the most reduction side of the variable magnification optical system, and which is fixed when magnification of the variable magnification optical system is changed;
• and
• a plurality of lens groups that are arranged between the first lens group and the final lens group, and which move when magnification of the variable magnification optical system is changed, and the number of the plurality of lens groups being less than or equal to three,
• wherein the reduction side of the variable magnification optical system is telecentric, and
• wherein a stop is arranged in the final lens group, thereby setting the numerical aperture of the variable magnification optical system constant through the entire range of variable magnification, and
• wherein the following formulas (18) and (19) are satisfied:
• 5.0<Bf×Zr2/Imφ (18),
• and
• L/Imφ<12.5 (19),
• where
• Bf:
• back focus in air of entire system at wide angle end,
• Zr:
• ratio of magnification at telephoto end to magnification at wide angle end,
• Imφ:
• diameter of a maximum effective image circle on the reduction side of the variable magnification optical system, and
• L:
• total lens thickness when projection distance is infinity.