US Patent 10539766 Projection optical system and projection image display device

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<0.9  (2).