US 12,405,446 B2
Optical system and image pickup apparatus having the same
Naoto Doujou, Tochigi (JP)
Assigned to CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Sep. 15, 2023, as Appl. No. 18/368,603.
Application 18/368,603 is a division of application No. 17/341,424, filed on Jun. 8, 2021, abandoned.
Claims priority of application No. 2020-108208 (JP), filed on Jun. 23, 2020.
Prior Publication US 2024/0012222 A1, Jan. 11, 2024
Int. Cl. G02B 9/12 (2006.01); G02B 5/00 (2006.01); G02B 9/06 (2006.01); H04N 23/23 (2023.01)
CPC G02B 9/12 (2013.01) [G02B 5/005 (2013.01); G02B 9/06 (2013.01); H04N 23/23 (2023.01)] 15 Claims
OG exemplary drawing
 
1. An optical system configured to image an object with light with a wavelength of 8 μm or longer, the optical system comprising:
a first lens having a negative refractive power;
a second lens having a positive refractive power and closer to an image plane than the first lens;
a third lens having a positive refractive power and closer to the image plane than the second lens;
a diaphragm; and
an optical element having an aspherical surface and disposed at a position different from that of the diaphragm,
wherein in a section including an optical axis, a thickness of the optical element is minimum at a position other than an on-axis and an outermost off-axis, and
wherein the following conditional expression is satisfied:
0.0<|f/Pf1|<0.3
where f is a focal length of the optical system, and Pf1 is a focal length of the optical element;
wherein the following conditional expression is satisfied:
0.1<|f1/f|<5.0
where f1 is a focal length of the first lens.