One of the disappointments for me with the RF-S system is the normal kit zoom range from 18-45 instead of 15-45mm.

In this patent application, Canon sets out to create a 15-45mm that hopefully isn’t plagued with the same quality assurance issues as its older EF-M brother. I swear I went through 5 copies until I finally got one that was on point and quite good. Once I did, I loved the focal range having been used of the 18-55mm kit zooms in the past, the 15-18mm was well appreciated by myself.

In this patent application, Cann wants a small lens with spherical aberrations and others more corrected than prior patents allowed for.

However, in the zoom lens disclosed in Patent Document 1, the entire lens system is large and it is not possible to achieve sufficiently high image quality. Furthermore, in the zoom lens disclosed in Patent Document 2, various aberrations such as spherical aberration and coma aberration are not sufficiently corrected. An object of the present invention is to provide a zoom lens with good optical performance over the entire zoom range.

The EF-M 15-45mm is quite similar in terms of optical design. This design appears to be missing one element between L11 and L12, otherwise it’s a very similar design.

The back focus on the embodiments is quite tight, which makes me wonder if this was originally in the pipeline as a EF-M 15-45mm II, instead of an RF-S lens. However, even though the ingress into the mount is significant, there may still be enough room for the lens inside of the mount body to sit the rear element back that far. As such, I’m not putting this as an RF-S lens. It probably was Canon’s intention though as I doubt any designer was working on new EF-M designs in 2022.

The age of the RF-S 18-45 for the RF-S probably has little bearing on a newer 15-45 as Canon in the past had replaced an earlier kit lens on mirrorless fairly quickly (3 years).

Canon APS-C 15-45mm F3.5-6.3

                 Wide-angle  Intermediate  Telephoto
focal length        15.36       29.82        43.10  
F number             3.60        5.10         6.44  
Half angle of view  35.76       23.75        17.59  
Lens total length   76.36       68.85        73.51  
BF                  10.45       10.45        10.45  

Canon APS-C 15-45mm F3.5-6.3

                 Wide-angle  Intermediate  Telephoto
focal length        15.37        29.58       43.10  
F number             3.60         5.10        6.44  
Half angle of view  35.41        24.79       17.59  
Lens total length   79.34        71.19       76.32  
BF                  10.18        10.18       10.18  

Canon APS-C 16-45mm F3.5-6.3

                 Wide-angle  Intermediate  Telephoto
F number             3.60         5.10        6.44  
focal length        16.23        34.90       43.10
F number             3.61         5.10        6.44
Half angle of view  32.27        20.40       17.59
Lens total length   88.10        84.74       88.68  
BF                  10.87        10.87       10.87 

Source: Japan Patent Office: 2023-182958

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