Projection optical system and projection image display device

A projection optical system comprising:

• a first lens unit adapted to make an enlargement-side imaging surface located on an enlargement side and an intermediate image conjugate with each other;
• a second lens unit adapted to make the intermediate image and a reduction-side imaging surface located on a reduction side conjugate with each other;
• and
• a first light path folding element and a second light path folding element adapted to fold a light path,
• wherein the first light path folding element is disposed between the first lens unit and the second lens unit,
• wherein the second light path folding element is disposed inside the second lens unit,
• wherein the first lens unit has positive power,
• wherein the second lens unit has negative power,
• wherein defining a focal distance on a d-line of the first lens unit as fU1, a focal distance on a d-line 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, following conditional expression (1) and conditional expression (2) are satisfied:
• −0.3<fU1/fU2<−0.005 (1)
• 0.5<LLU1/LLU2<0.9 (2),
• wherein the second lens unit is provided with, in the order from the side of the intermediate image toward the side of the reduction-side imaging surface, a second lens unit intermediate image-side first lens, which is provided with a concave surface on the intermediate image side and has positive power, a second lens unit intermediate image-side second lens, which is provided with a concave surface on the reduction-side imaging surface side and is provided with negative power, and a second lens unit intermediate image-side third lens having positive power,
• wherein the second lens unit intermediate image-side first lens, the second lens unit intermediate image-side second lens, and the second lens unit intermediate image-side third lens are located between the first light path folding element and the second light path folding element, and
• wherein defining a refractive index on a d-line of the second lens unit intermediate image-side first lens as nd (21), and an Abbe number as vd (21), a refractive index on a d-line of the second lens unit intermediate image-side second lens as nd (22), and an Abbe number as vd (22), following conditional expression (3) and conditional expression (4) are satisfied:
• |nd(22)−nd(21)|<0.4 (3)
• |vd(21)−vd(22)|<30 (4).