Projection optical system and projector
A projection optical system includes a first lens group having negative power, a second lens group having positive power and disposed at a reduction side of the first lens group, and a third lens group having positive power and disposed at the reduction side of the second lens group. The first lens group includes at least three negative lenses. The second lens group includes at least one positive lens. The third lens group includes a plurality of positive lenses. The at least three negative lenses of the first lens group are each a single lens. The third lens group includes a jointed lens including at least one of the plurality of positive lenses. NA is a reduction-side numerical aperture, Dst is a distortion aberration at a reduction-side maximum image height, and the projection optical system satisfies Conditional Expressions (1) and (2), 0.2<NA (1) −45%<Dst<−10% (2).
1. A projection optical system comprising:
a first lens group having negative power and including at least three negative lenses;
a second lens group having positive power and including at least one positive lens, the second lens group disposed at a reduction side of the first lens group; and
a third lens group having positive power and including a plurality of positive lenses, the third lens group disposed at the reduction side of the second lens group,
wherein the at least three negative lenses of the first lens group are each a single lens,
the third lens group includes a jointed lens including at least one of the plurality of positive lenses, and
NA is a reduction-side numerical aperture, Dst is a distortion aberration at a reduction-side maximum image height, and the projection optical system satisfies Conditional Expressions (1) and (2) below:
0.2<NA (1)
−45%<Dst<−10% (2).
2. The projection optical system according to claim 1 , wherein f is a focal length of the entire projection optical system, f1 is a focal length of the first lens group, f23 is a combined focal length of a combination of the second lens group and the third lens group, and the projection optical system satisfies Conditional Expressions (3) and (4) below:
0.8<| f 1/ f|< 2.2 (3)
0.2<| f 1/ f 23|<0.6 (4).
3. The projection optical system according to claim 1 , wherein f2 is a focal length of the second lens group, N is an average of refractive indices of the positive lenses included in the second lens group, V is an average of Abbe numbers, and the projection optical system satisfies Conditional Expression (5), (6), and (7) below:
4.0< f 2/ f< 10.0 (5)
N> 1.65 (6)
V< 35 (7)
4. The projection optical system according to claim 1 ,
wherein the third lens group includes a reduction-side first lens arranged on a position closest to the reduction side,
the reduction-side first lens is a positive lens having a convex surface facing the reduction side, and
f3 is a focal length of the third lens group, and the projection optical system satisfies Conditional Expression (8) below:
2.0< f 3/ f< 6.0 (8)
5. The projection optical system according to claim 1 , wherein one of the lenses included in the first lens group has an aspheric surface facing an enlargement side.
6. A projector comprising:
the projection optical system according to claim 1 ;
a light source; and
a light modulator disposed in a reduction-side conjugate plane of the projection optical system, the light modulator modulating light emitted from the light source to form a projection image having distortion which corrects a distortion aberration generated in the projection optical system,
wherein the projector projects an enlarged image in which the distortion aberration is corrected to an enlargement-side conjugate plane of the projection optical system.