A new Canon patent application for relatively fast prime lenses.

Canon patent application 2023149130 (Japan, published 10/12/2023) discusses optical formulas for prime lenses for the RF mount:

• RF 70mm F2
• RF 70mm F2.8
• RF 75mm F2.4
• RF 85mm F2.8

From the patent literature:

• The present invention provides an optical system that is small and lightweight, yet can satisfactorily correct various aberrations including chromatic aberration and obtain high optical performance, and an imaging device having the same.
• BACKGROUND ART
  In recent years, there has been a strong demand for optical systems used in imaging devices to have a compact overall lens system and high optical performance including chromatic aberration correction.
• Generally, in a telephoto type optical system, as the focal length becomes longer, the entire lens system becomes larger and its mass increases. In order to miniaturize the optical system with a telephoto power arrangement, it is effective to strengthen the positive refractive power on the object side and the negative refractive power on the image side, but it is effective to increase the positive refractive power on the object side and the negative refractive power on the image side. Challenges arise in balancing both work and life.
• Furthermore, in an optical system compatible with a large image sensor, it is important to perform focusing quickly using a small and lightweight lens group, and with less burden on the driving device. In a telephoto optical system, in order to easily perform focusing and to reduce aberration fluctuations during focusing, it is important to appropriately set the lens configuration of each lens group.
• Patent Document 1 discloses that a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group are arranged in order from the object side to the image side. An optical system is disclosed in which the distance between matching lens groups is varied.
• However, in the optical system described in Patent Document 1, the number of lenses constituting the optical system is large, and the optical system cannot be sufficiently miniaturized.
• The present invention provides an optical system that is small and lightweight, yet can satisfactorily correct various aberrations including chromatic aberration and obtain high optical performance, and an imaging device having the same.

Example 1

• Focal length: 70.00
• F value: 2.06
• Half angle of view: 17.17
• Image height: 21.64
• Total length: 78.88
• Back focus: 16.48

Example 2

• Focal length: 70.00
• F value: 2.83
• Half angle of view: 17.17
• Image height: 21.64
• Total length: 68.97
• Back focus: 17.41

Example 3

• Focal length: 85.00
• F value: 2.83
• Half angle of view: 14.28
• Image height: 21.64
• Total length: 83.01
• Back focus: 17.55

Example 4

• Focal length: 75.00
• F value: 2.40
• Half angle of view: 16.09
• Image height: 21.64
• Total length: 86.00
• Back focus: 15.64

More Canon patents are listed here.