Patent ID: 11914121
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 7:
8. A reduction optical system disposed on an image side of a main optical system, a composite focal length of the main optical system and the reduction optical system being shorter than a focal length of the main optical system, the reduction optical system comprising:
a first lens element disposed closest to an object side and having a positive refractive power;
a second lens element disposed closest to an image side and having a positive refractive power; and
a positive lens and a negative lens disposed between the first lens element and the second lens element,
wherein following conditional expression is satisfied:

0.440≤fp1/f<1.500,

where fp1 is a focal length of the first lens element, and f is a focal length of the reduction optical system, and
wherein the reduction optical system includes a first positive lens which satisfies following conditional expressions:

1.900≤Nph 

where Nph is a refractive index of the first positive lens.