Japan Patent Office has published publically a patent application from Canon that covers a specific lens type for APS-C cameras would be certainly welcomed.
Looking through the application makes me wonder if the initial designs were not for the EF-M mount versus the RF-S mount, but I think it’s pretty safe to say that Canon is not going to design any more lenses specifically for the EF-M mount.
The reason I think this is the back focus distances mentioned in the designs. All these lenses have a pretty shallow back focus instance (which is the distance between the last element and the sensor plane). There is a limit to how far back a lens can stick into the camera body because the shutter assembly will get in the way, but this should not be an impact in these designs with either the RF-S or EF-M mounts, however, lenses that stick fairly deep into the camera body are uncommon.
All these lenses have some form of image stretching at the wide end but it’s relatively minimal. I’ve been totally against Canon doing this as it does incur a slight resolution loss in the wide end but they seem to be ignoring my protests.
RF-S 15-70mm F4.0
Canon has done only one constant aperture APS-C lens before, the well-regarded Canon EF-S 17-55 F2.8. However, this would be a very welcomed lens for just about any high-end APS-C kit. It’s also relatively compact being the shortest length of around 80mm (the length includes the back focus distance).
The lens design particulars are;
Focal length 15.45 36.03 67.94
F-number 4.12 4.12 4.12
Half angle of view (°) 41.27 19.59 10.60
Image height 12.66 13.66 13.66
Total lens length 100.14 108.00 120.23RF-S 15-70mm F2.8-4.0
This sounds like a great lens, and if Canon did this I would immediately be purchasing an RF-S camera body to go with it. Generally speaking, there’s a bit of stretching aka, loss of resolution on the wider end that Canon seems to be overly fond of doing these days, but it’s not excessive.
It’s also relatively compact being the shortest length of around 80mm (the length includes the back focus distance).
I would expect Canon to be able to make this a bit less expensive than the F4 constant aperture lens shown above.
The lens particulars are as follows;
Focal length 15.45 36.49 68.04
F-number 2.88 3.86 4.12
Half angle of view (°) 41.38 19.53 10.61
Image height 12.66 13.66 13.66
Total lens length 100.32 110.44 118.71 RF-S 15-85mm F2.8-5.6
This next one I would find a bit more likely that I would purchase over the design just above because of the little higher zoom range than the proceeding design as it features a slightly higher zoom ratio of 5.33x versus 4.66. Usually, that comes as a tradeoff of performance, but people are buying these lenses for the convenience of all-in-one travel kit. Starting at 15mm versus 18mm and also faster on the wide end when we compare this against the already existing 18-150mm makes this a better overall travel lens in my opinion.
The lens design particulars are;
Focal Length 15.45 36.29 83.77 F-Number 2.88 4.00 5.80 Half Angle of view (°）41.36 19.65 8.71 Image Height 12.66 13.66 13.66 Total Lens Length 101.54 116.35 133.85
Considering the extreme lack of RF-S lenses, I would personally happily take any of these lenses. Heck, any of these lenses would get me to migrate over to the RF-S mount. These lenses were always some of the most commonly asked-for lenses on the EF-M mount, so it’s nice to see Canon still exploring mirrorless options.
Of course, with any patent application, there are no guarantees that Canon is actually going to develop what is mentioned in the application. But what it does indicate is what Canon is researching as potential options.
Source: Japan Patent Office 2023-112298
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