Patent ID: 11966099
Assignee: CANON KABUSHIKI KAISHA
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H | IPC G  H

Claim 0:
1. A converter lens which has a negative refractive power and increases a focal length of an entire system when arranged on an image side of a master lens, the converter lens consisting of:
a first lens unit having positive refractive power; and
a second lens unit having negative refractive power and arranged on an image side of the first lens unit,
wherein the first lens unit consists of a negative lens and a first positive lens,
wherein three negative lenses are included in the converter lens, and
wherein the following inequalities are satisfied:

1.92<Ndave<2.10,

−1.40<f1/f≤−0.670, and

0.10<sk/TD<0.35,

where Ndave represents an average refractive index at a d-line of a material of the three negative lenses included in the converter lens, f1 represents a focal length of the first lens unit, f represents a focal length of the converter lens, sk represents an air-converted length from a surface of the converter lens closest to the image side to an image plane while the converter lens is arranged on the image side of the master lens, and TD represents a length on an optical axis from a surface of the converter lens closest to the object side to a surface closest to the image side.