In this patent application (2024-023099) Canon describes quite a few different full-frame super ultra-wide zoom lenses. Now with Canon just having released the pretty incredible Canon RF 10-20mm f/4 L IS STM, this is probably some of Canon's prior research that happened with that lens.
Canon in their own patent-ish words;
An object of the present invention is to provide a zoom lens that is small and has good optical characteristics, and an imaging device and an imaging system including the zoom lens.
I think we all want that for every possible zoom lens, Canon.
Now to the embodiments. Usually, when Canon says we want to make things small, there is some compromise. Since the RF system came into being that usually translates into the image circle diameter the lens can project. Canon, like all other mirrorless manufacturers, is no longer limited by the optical viewfinder in this regard. So Canon feels the loss of resolution is acceptable for the sake of portability and costs. In a lot of cases, if the lens is good even with its reduced image circle, only a purist (or me) complains bitterly about it. During normal photography, unless the stretching back to the full image circle is severe, we really can't tell in our photos.
In case you are reading one of these from me for the first time (shame, you've missed a lot!) half image height on the patent applications is the radius of the projected image circle. So this needs to be around half the diagonal sensor measurement to fully cover the sensor area, which for full frame is 21.60-21.64. You can get a reference for all the various sensor sizes from Wikipedia, which is where I go every time I'm doing up one of these patents and I see something odd.
The next important factor also determines what mount the embodiment is for, and that's the back focus distance. That is the distance from the last element on the design to the sensor plane. On an RF camera, the focal plane distance is 20.00mm (distance from the sensor plane to the outer edge of the mount), so if the back focus distance is less than 20.00mm we know the back element is recessed into the mount.
So with these patent embodiments, we are seeing image stretching and a very short back focus distance, all of them are certainly possible – but we already know what Canon decided to do here as they released the Canon RF 10-20mm f/4 L IS STM. The second example embodiment has an element layout that very closely resembles that of the production RF 10-20mm f/4 L IS STM. This is curious because it certainly would tell us what the extreme limit to back focus distance is if this was the real design that was used (the embodiment states 10.50mm) and as you can see by the Canon element layout for the Canon RF 10-20mm f/4 L IS STM it does sit inside the mount quite a bit (the Canon image shouldn't be considered to scale).
Also, the size of the lens seems to match well with the Canon RF 10-20mm, which has a lens length of 112mm, and the embodiment shows a length of 105mm. Allowing for the shrouds surrounding the front and rear of the lens, I can see this easily adding 6mm to the length forecasted.
Canon RF 10-20mm F4
Wide angle Intermediate Telephoto focal length 10.33 15.00 19.39 F number 4.08 4.08 4.12 Half angle of view 61.36 55.26 48.13 Image height 18.92 21.64 21.64 Lens total length 128.82 122.35 123.27 Back Focus 12.13 12.13 12.13
Wide angle Intermediate Telephoto focal length 10.33 15.00 19.39 focal length 9.20 16.04 17.90 F Number 4.08 4.08 4.12 Half angle of view 64.04 53.45 50.40 Image height 18.90 21.64 21.64 Lens total length 125.26 118.57 119.35 Back Focus 10.50 10.50 10.50
Canon RF 10-24mm F4
Wide angle Intermediate Telephoto focal length 11.30 16.61 23.90 F number 4.08 4.08 4.12 Half angle of view 59.29 52.49 42.15 Image High 19.02 21.64 21.64 Lens total length 129.79 125.70 129.33 Back Focus 14.54 12.80 10.54
Canon RF 10-24mm F2.8
Wide angle Intermediate Telephoto focal length 11.30 14.97 22.00 F number 2.89 2.89 2.89 Half angle of view 59.44 55.32 44.52 Image height 19.14 21.64 21.64 Lens total length 137.35 129.65 125.58 Back Focus 13.50 12.41 10.50
Canon RF 10-20mm F4
Wide angle Intermediate Telephoto focal length 10.30 16.00 19.60 F number 4.08 4.08 4.12 Half angle of view 61.86 53.52 47.83 Image height 19.26 21.64 21.64 Lens total length 114.35 105.41 104.44 Back Focus 14.75 21.84 26.22
Canon RF 10-24mm F2.8
Wide angle Intermediate Telephoto focal length 11.30 16.61 23.90 focal length 10.30 15.22 19.80 F number 2.89 3.50 4.12 Half angle of view 61.76 54.87 47.54 Image height 19.18 21.64 21.64 Lens total length 132.94 126.11 127.01 Back Focus 11.35 11.35 11.35
As with all patent applications, this is a look into Canon's research. I think it's very highly likely that this patent application became reality with the release of the Canon RF 10-20mm f/4 L IS STM.
Source: Japan Patent Application 2024-023099
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