Canon Patent Application: Mirrorless Full frame 20mm F1.8 and 24mm F1.8

In this patent application, Canon is requesting a patent for various optical mirrorless lens designs. The patent is description is concerning creating wide angle lenses that are small and light with a controlled amount of aberrations.

In a wide-angle lens optical system, as the focal length becomes shorter, more aberrations such as chromatic aberration of magnification and curvature of field occur among various aberrations. To correct them, increase the overall length of the lens. Or, it is necessary to increase the number of constituent lenses, but the optical system becomes large. Therefore, in the wide-angle lens optical system, it is an issue to achieve both high optical performance and weight reduction of the optical system.

If you notice I don't suggest these lenses are for the Canon RF system - because I do think the back focus distance is too short for the RF system.  The sensor to mount distance of the RF system is 20mm.  The embodiments show a backfocus distance (the distance between the rear element and the sensor) as being 11-12mm.  This means the lens would have to sit into the mount 8mm which I think is too much of an ingress. 

This patent was filed after the RF mount already announced and available, which makes it a curious patent application.

A few of the embodiments are shown below.

Canon 20mm F1.8

Focal length                 20.60  
F number                      1.85  
Half angle of view (degrees) 46.40  
Image height                 21.64  
Lens total length            88.73  
BF                           11.72 

Canon 24mm F1.8

Focal length                 23.28  
F number                      1.85  
Half angle of view (degrees) 42.90  
Image height                 21.64  
Lens total length            93.32  
BF                           12.72  

While this patent application is not for the RF mount, I do find it encouraging that Canon is researching small and lightweight ultra wide lenses with good optical quality.

Japan Patent Application 2021-071624

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