Canon Patent: Fish-eye Lens With Reduced Distortion

A Canon patent for a new fish-eye lens.

Canon patent application JP2025-12993 (Japan, published 01/24/2025) discusses optical formulas for a fish-eye lens with a rear conversion lens to reduce distortion. From the patent literature:

• By adding another optical system to a master optical system, distortion is suppressed while avoiding an increase in the size of the entire optical system.
• Description of the Related Art: As a method for obtaining a wide-angle lens with low distortion from a fisheye lens, Patent Document 1 discloses a method for converting the projection method of a fisheye lens to a general projection method by placing an aspherical dome-shaped lens with negative refractive power on the object side of the fisheye lens (master optical system). Patent Document 2 discloses a method for changing the projection method by exchanging an intermediate portion between the object side and image side of the optical system.
• Placing a dome lens on the object side of a fisheye lens as in Patent Document 1 leads to an increase in size of the entire optical system. Also, the method of replacing an intermediate part of the optical system as in Patent Document 2 requires replacement work and the configuration to enable replacement becomes complicated.
• The present invention provides a lens device that can suppress distortion while avoiding an increase in the size of the entire optical system by adding another optical system to the master optical system.

Example 1-A

• Focal length: 8.25-15.48
• F-number: 4.12
• Half angle of view: 53.50-54.42
• Image height: 11.15-21.64
• Overall length: 105.00
• Back focus: 25.50-40.85

Example 1-B

• Focal length: 15.41
• F-number: 4.12
• Half angle of view: 54.54
• Image height: 21.64
• Overall length: 105.00
• Back Focus: 18.25

Example 3-A

• Focal length: 16.11
• F-number: 2.50
• Half angle of view: 53.33
• Image height: 21.64
• Overall length: 81.19
• Back focal length: 22.76

Example 3-B

• Focal length: 18.69
• F-number: 2.90
• Half angle of view: 49.17
• Image height: 21.64
• Overall length: 88.32
• Back focal length: 9.91

Example 4-A

• Focal length: 17.67
• F-number: 2.50
• Half angle of view: 50.76
• Image height: 21.64
• Overall length: 100.05
• Back Focus: 41.09

Example 4-B

• Focal length: 16.71
• F-number: 2.36
• Half angle of view: 52.32
• Image height: 21.64
• Overall length: 100.06
• Back focal length: 9.61

More Canon patents are listed here.

[via asobinet]