Here is a new Canon patent application for a bunch of lenses, of which one might already have releases.

Canon patent application 2024082112 (Japan, published 6/19/2024) discusses optical formulas for three lenses:

• RF-S 33mm f/1.8
• RF 28mm f/2.8 (might refer to this lens)
• RF 24mm f/2.8

From the patent literature:

• [Background Art] With the miniaturization and high pixel count of image sensors, optical systems used in imaging devices are required to be small and have high optical performance. In order to satisfy these requirements, Patent Document 1 proposes an optical system consisting of a first lens with positive refractive power, a second lens with negative refractive power, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in order from the object side to the image side. The lens surface on the object side of the first lens is convex near the optical axis. The lens surface on the image side of the second lens is concave near the optical axis. The lens surface on the object side of the third lens is convex near the optical axis. The lens surface on the image side of the fourth lens is convex near the optical axis. The lens surface on the object side of the fifth lens is convex near the optical axis. The lens surface on the image side of the sixth lens is concave near the optical axis.
• In order to reduce the overall length of an optical system, it is effective to adopt a telephoto type power arrangement and strengthen the positive refractive power on the object side and the negative refractive power on the image side. However, when the power arrangement of a telephoto type is strengthened, a large pincushion distortion occurs, making it difficult to simultaneously correct distortion and curvature of field with a limited number of lenses. In addition, when the power arrangement of a telephoto type is strengthened, the back focus becomes shorter and the exit angle of the off-axis light beam becomes larger.
• The optical system described in Patent Document 1 employs a telephoto power arrangement to reduce the overall length, and uses multiple aspheric lenses to correct distortion and curvature of field, but the Petzval sum of the entire system is large and the exit angle of the off-axis light beam is also large. Therefore, when attempting to apply the optical system described in Patent Document 1 to an imaging device with a large image sensor, the correction of curvature of field and the reduction in peripheral light amount become issues.
• The present invention provides an optical system that is small, lightweight, and has high optical performance.
• In the optical system L0 of each embodiment, the final lens Lp is preferably made of plastic. The diameter of the final lens Lp is generally large, and using glass as the material for the final lens Lp is not preferable because the lens weight becomes heavy.

Example 1

• Focal length: 28.50
• F-number: 2.86
• Half angle of view: 37.20
• Image height: 21.64
• Overall length: 42.64
• Back Focus: 13.25

Example 2

• Focal length: 28.50
• F-number: 2.55
• Half angle of view: 37.20
• Image height: 21.64
• Total length: 42.90
• Back Focus: 12.46

Example 3

• Focal length: 24.50
• F-number: 2.88
• Half angle of view: 41.45
• Image height: 21.64
• Total length: 47.90
• Back Focus: 11.28

Example 4

• Focal length: 33.08
• F-number: 1.85
• Half angle of view: 22.44
• Image height: 13.66
• Overall length: 41.00
• Back Focus: 11.91

More Canon patents are listed here.

[via asobinet]