Abstract: An optical system includes a first optical element including a first reflective area having a convex shape toward a magnification side, a second optical element including a second reflective area having a convex shape toward the magnification side, and a light shielding member disposed between the first optical element and the second optical element. Light from the magnification side travels to a reduction side through the second reflective area, the first reflective area, and a refractive area of the second optical element in order. The light shielding member is disposed between light entering the second reflective area and light entering the first reflective area in a first cross-section including an optical axis.

Abstract: An image pickup apparatus including an optical system and an image pickup element. The optical system includes a first refractive surface disposed closest to an object, a first reflection surface, and a second reflection surface. A light receiving surface of the image pickup element is disposed at only one side with respect to the optical axis and at a position closer to the optical axis than an intersection between a straight line connecting an intersection on the first refractive surface and an intersection on an imaginary extension surface of the second reflection surface and an imaginary extension surface of the light receiving surface. Expression 1.5?L2/L1?6.5 is satisfied where L1 is an interval between the first reflection surface and the second reflection surface, and L2 is an interval between the first reflection surface and the light receiving surface.

Abstract: An optical system includes a first optical element including a first reflecting region having a convex shape toward an enlargement side, a second optical element having a reduction-side surface having a convex shape toward the enlargement side, and a third optical element having an enlargement-side surface having a convex shape toward the enlargement side, wherein the reduction-side surface of the second optical element or the enlargement-side surface of the third optical element includes a second reflecting region, wherein the third optical element includes a refracting region having positive power, and wherein light from the enlargement side proceeds to a reduction side sequentially through a refracting region of the first optical element, the second reflecting region, the first reflecting region, a refracting region of the second optical element, and the refracting region of the third optical element.

Abstract: An image pickup apparatus including an optical system and an image pickup element. The optical system includes a first refractive surface disposed closest to an object, a first reflection surface, and a second reflection surface. A light receiving surface of the image pickup element is disposed at only one side with respect to the optical axis and at a position closer to the optical axis than an intersection between a straight line connecting an intersection on the first refractive surface and an intersection on an imaginary extension surface of the second reflection surface and an imaginary extension surface of the light receiving surface. Expression 1.5?L2/L1?6.5 is satisfied where L1 is an interval between the first reflection surface and the second reflection surface, and L2 is an interval between the first reflection surface and the light receiving surface.

Abstract: An optical system includes a first optical element including a refractive surface convex to an enlargement side, a second optical element including a catadioptric surface convex to the enlargement side, a third optical element including a reflective surface of a concave shape with respect to light incident thereon, and a fourth optical element that is a refractive element having positive power, wherein light from the enlargement side travels to a reduction side via the refractive surface, a reflective region of the catadioptric surface, the refractive surface, the reflective surface, the refractive surface, a refractive region of the catadioptric surface, and the fourth optical element in succession, and wherein a medium between the refractive surface and the reflective surface has a refractive index lower than that of the first optical element.

Abstract: An optical system includes a first optical element including a first reflecting region having a convex shape toward an enlargement side, a second optical element having a reduction-side surface having a convex shape toward the enlargement side, and a third optical element having an enlargement-side surface having a convex shape toward the enlargement side, wherein the reduction-side surface of the second optical element or the enlargement-side surface of the third optical element includes a second reflecting region, wherein the third optical element includes a refracting region having positive power, and wherein light from the enlargement side proceeds to a reduction side sequentially through a refracting region of the first optical element, the second reflecting region, the first reflecting region, a refracting region of the second optical element, and the refracting region of the third optical element.

Abstract: A catadioptric optical system of the present invention includes a first imaging optical system that collects a light beam from an object, and a second imaging optical system including a refractive portion that forms an intermediate image by receiving a light beam from the first imaging optical system and to form an image of the intermediate image on an image plane, the first imaging optical system includes a first optical element and a second optical element, a reflection surface of the reflective portion of the first optical element and a reflection surface of the reflective portion of the second optical element are disposed so as to face each other, and an aperture stop is disposed between the first optical element and the second optical element.

Abstract: A catadioptric optical system of the present invention includes a first imaging optical system that collects a light beam from an object, and a second imaging optical system including a refractive portion that forms an intermediate image by receiving a light beam from the first imaging optical system and to form an image of the intermediate image on an image plane, the first imaging optical system includes a first optical element and a second optical element, a reflection surface of the reflective portion of the first optical element and a reflection surface of the reflective portion of the second optical element are disposed so as to face each other, and an aperture stop is disposed between the first optical element and the second optical element.

Abstract: A coupling lens for chromatic aberration correction is placed between a light source and an objective lens for focusing light beams with a plurality of wavelengths on an information recording surface of an optical recording medium, and at least one surface of the coupling lens includes a plurality of annular zones having a step concentric with an optical axis. The coupling lens is designed so that when a wavelength ?1=380 to 430 nm and a height of the step is d=m1?1/(n1?1) where m1 is an actual number and n1 is a refractive index of the coupling lens at the wavelength ?1, 9.9?m1?10.1 is satisfied.

Abstract: A coupling lens for chromatic aberration correction is placed between a light source and an objective lens for focusing light beams with a plurality of wavelengths on an information recording surface of an optical recording medium, and at least one surface of the coupling lens includes a plurality of annular zones having a step concentric with an optical axis. The coupling lens is designed so that when a wavelength ?1=380 to 430 nm and a height of the step is d=m1?1/(n1?1) where m1 is an actual number and n1 is a refractive index of the coupling lens at the wavelength ?1, 9.9?m1?10.1 is satisfied.