Abstract: An optical system includes a first lens having negative refractive power, a stop, a second lens having positive refractive power, an aperture stop, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power, with the lenses sequentially arranged from the magnifying side toward the demagnifying side. The third and fourth lenses are bonded into a doublet, which has negative refractive power. One of the fifth and sixth lenses is made of plastic and has aspherical surfaces on opposite sides, and the other is made of glass. The portion on the demagnifying side of the sixth lens is a telecentric portion. Conditional Expression (1) below is satisfied, SD12/SD2<0.9??(1) where SD12 represents the effective radius of the stop, and SD2 represents the effective radius of the second lens.

Abstract: A projection system includes a first optical system and a second optical system. The second optical system includes a first lens group disposed on an enlargement side of an intersection position where a chief ray of an off-axis beam having a maximum angle of view intersects with an optical axis of the projection system in the second optical system, a second lens group disposed on the reduction side of the intersection position and having negative power, and a third lens group disposed on the reduction side of the second lens group and having positive power. The second lens group includes a first lens having positive power, a second lens disposed on the reduction side of the first lens and having positive power, and a third lens disposed on the reduction side of the second lens and having negative power. The third lens group includes two lenses each having positive power.