US 12,292,557 B2
Optical system, image pickup apparatus, and projection apparatus
Kana Kobayashi, Tochigi (JP)
Assigned to Canon Kabushiki Kaisha, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Sep. 13, 2021, as Appl. No. 17/473,768.
Claims priority of application No. 2020-160429 (JP), filed on Sep. 25, 2020.
Prior Publication US 2022/0099951 A1, Mar. 31, 2022
Int. Cl. G02B 17/08 (2006.01); G02B 5/00 (2006.01)
CPC G02B 17/08 (2013.01) [G02B 5/005 (2013.01); G02B 17/0832 (2013.01)] 18 Claims
OG exemplary drawing
 
1. An optical system comprising:
an entrance unit, a first reflective surface, a second reflective surface, a third reflective surface, an exit unit, and a rear unit that is a dioptric optical system located on an image side of the exit unit,
wherein the entrance unit is rotationally symmetric around a central axis,
wherein incident light from the entrance unit intersects the central axis and enters the first reflective surface,
wherein reflected light from the first reflective surface enters the second reflective surface without intersecting the central axis,
wherein reflected light from the second reflective surface enters the third reflective surface,
wherein the rear unit includes a diaphragm coaxial with the central axis, and a cemented lens located on the image side of the diaphragm, and
wherein the following inequality is satisfied:
−0.90<(RP2+RP1)/(RP2−RP1)≤0.00
where RP1 is a radius of curvature on an object side of a positive lens included in the cemented lens, and RP2 is a radius of curvature on an image side of the positive lens.