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. This new design 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   120.23

RF-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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57 comments

  1. 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.
    I found that the stretched corners of the RF 14-35/4L as processed with DxO PhotoLab had similar extreme corner sharpness and detail as the EF 11-24/4L. Optical correction (i.e., the design of a lens) isn’t perfect…even when the image circle covers the full image frame, corners can be soft.
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  2. I’d prefer straight cropping over stretching, but I see where people would get very upset at getting a 22MP picture instead of 24.
    And of course you don’t get any stretching when shooting RAW, so I’m good either way.
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  3. The fact that they applied for a patent means that they did develop it and for sure have a least one working engineering sample.
    they use computer aided design to develop the optical formulas. no need to go old school.
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  4. > 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.

    @Canon Rumors Guy if you have an image that is the worse for this technique I'd enjoy seeing it. I've got an open mind if there are cases this is bad somehow, but from an engineering level, it basically blurs images by up to a half pixel linearly. From my studies of resolution (the SHOOTOUT posts on your lens forum here) I have doubts this is normally going to be very visible unless you're using native resolution and I don't think that's that common.
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  5. > 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.

    @Canon Rumors Guy if you have an image that is the worse for this technique I'd enjoy seeing it. I've got an open mind if there are cases this is bad somehow, but from an engineering level, it basically blurs images by up to a half pixel linearly. From my studies of resolution (the SHOOTOUT posts on your lens forum here) I have doubts this is normally going to be very visible unless you're using native resolution and I don't think that's that common.
    Stretching is bad for astro and only OK for landscapes if you do framing or crop in for the rule of thirds.
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  6. Stretching is bad for astro and only OK for landscapes if you do framing or crop in for the rule of thirds.
    I completely agree with that, but I have a slightly different take on the stretching based on the lenses I have: I have a 17-40L, which has very bad corners. The stretched corners on the non-L RF16mm have much more sharpness and detail at f/2.8 than the 17-40L has at any aperture.

    I'd still like non-stretched corner for even better results, but for me, the RF16 is already a massive improvement over the lens I used previously. I'd likely feel different if I hadn't used the 17-40L before :)
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  7. Stretching is bad for astro and only OK for landscapes if you do framing or crop in for the rule of thirds.
    How so? It's taking a scene and producing a rectilinear file, right? How can you even detect that the intermediate format of the information--an image projected on the sensor--had distortion, once you let the algo correct it? How is that not OK for landscapes in some situations? How not for astro?

    If you don't have an actual side-by-side comparison to show how this is bad, can you explain even what a person would look for to tell the difference? Between say the Canon RF16/2.8 that apparently uses this technique big-time, and some other 16mm lens of your choice that is perfectly rectilinear, or even a theoretically perfectly rectilinear one?
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  8. Stretching is bad for astro and only OK for landscapes if you do framing or crop in for the rule of thirds.
    Here are two images at 14mm, same scene, both 100% crops from the extreme corner. One is from a lens that has essentially zero geometric distortion at 14mm, and no distortion correction was applied. The other is from a lens that has serious barrel distortion to the point of black corners at 14mm, and thus requires 'stretching' to fill the frame. Based on your statement that stretching is bad, it should be obvious which is which. Is it?

    1.jpg

    2.jpg
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  9. I completely agree with that
    Why, I still ask? Three of you guys, who surely know what you're talking about, are convinced. What convinced you of this? Do you have a simple A/B comparison image? Do you have a technical explanation you can walk me through? I understand optics pretty well for someone outside the field, and general engineering principles as an aged engineer.


    I have a slightly different take on the stretching based on the lenses I have: I have a 17-40L, which has very bad corners. The stretched corners on the non-L RF16mm have much more sharpness and detail at f/2.8 than the 17-40L has at any aperture.

    I'd still like non-stretched corner for even better results, but for me, the RF16 is already a massive improvement over the lens I used previously. I'd likely feel different if I hadn't used the 17-40L before
    At first glance your 17-40 vs. 16/2.8 observations could be seen to support my point but to be honest I can't take a victory lap on that, it's a bit apples and orangutans once you reflect that one's a decade or whatever old, and a zoom, and using the old mount, and conversely the 16/2.8 is a shockingly low price point, etc. etc. Your example's really good, and maybe the best possible under the circumstances, but I feel we can't quite bet the farm on it.

    And specifically,
    I'd still like non-stretched corner for even better results
    again leads to the question: why do you believe non stretched would produce better results?

    ----------

    Here's my take. Lens development has a dozen (or more!) trade-offs. You can get more aperture for less sharpness, more sharpness for worse size and cost and weight, better cost for worse out-of-focus highlight behavior or worse lateral chromatic aberration, and so on. If we can take any given image defect, such as rectilinearity, and fix them in software nearly perfectly, that's as close as you can get to a free lunch, no? We don't have to improve rectilinearity at the expense of size or color fringes or cost! We can get it without hurting anything else.

    And that's just the first step. Once you realize how easily and accurately it can be fixed, you can actually use it as a toxic dumping ground. This is the important thing: we can then trade practically everything else off at the expense of rectilinearity! Improve size at the expense of rectilinearity. Then improve sharpness at the expense of rectilinearity. Improve LCA at the expense of rectilinearity. Improve flare at the expense of rectilinearity. Suddenly the lens is halfway towards being a fisheye... and yet... we've improved perhaps every aspect of the lens, at the expense of rectilinearity, then made the nightmare horrible resulting distortion simply magically disappear.

    Result is a $299 16/2.8 that's far sharper than the 14/2.8 of the 90s that cost 10-15x more in real terms and was 4x the weight. (645g vs 165g!)

    So how is this rectilinearity so easy to fix?

    Basically, we have to magnify (in this case), or shrink, pixels when converting from what the sensor saw to what's actually being output. This magnification is at worst something like 10% or so. It may look horrible, but it's not mathematically huge. If our source pixel overlaps a destination pixel once remapped, that destination pixel will be filled with the source pixel, and furthermore at most 10% of its area will crowd into neighboring pixels to the sides, and likewise vertically. (Could be evenly 5% each way, could be 10% all one way.) So that lowers contrast 10%. But of what? Only of 1-pixel-wide details that are in perfect focus, not running into diffraction limit, and not running into subject motion or camera motion-induced blur even at the most pixel-peeping level, not hidden under a high-ISO noise floor... and that are themselves perfectly aligned with a sensor pixel and not say split between two or four. At 8000 pix (R5) width and 36mm (full-frame sensor), that is 222 pix per mm, or 111 line pairs per millimeter.

    Again, changing the magnification in software will cut contrast as much as 10%... at 100 lp/mm. Canon doesn't even supply 100 lp/mm info. No-one does. No testing site even tests this, because such details do not exist outside of test charts. Why don't any tests even try to test this? When such a 1-pixel-wide scene feature falls between 4 pixels, your contrast may be as low as 25% anyway, even with a perfect lens in perfect focus, no subject or camera movement, no noise, and so on.


    In addition to the magnification issue, we have a movement issue. The image will move 10, 20, or even who knows, 100+ pixels, between where they physically hit the sensor, and where the software recomputes it. It sounds like it would get worse and worse... but it doesn't. This is because it can never be more than one pixel off some pixel in the output file. For instance even if a sensor pixel's value is moved exactly 100 pixels away, it will still be aligned with an output pixel 100% in this case. The worst any alignment can get is if the sensor pixel is split between four output pixels. That would lower your contrast 75%! Sounds bad, but again, what details are we talking about? Exactly as before: Only of 1-pixel-wide details that are in perfect focus, not running into diffraction limit, and not running into subject motion or camera motion-induced blur even at the most pixel-peeping level, with no sensor noise, and if the lens is otherwise perfect... and that are themselves perfectly aligned with a single sensor pixel and not say split between two or four.

    If you're having trouble picturing this, imagine you have a perfect black background and 1 white square on the test scene that is exactly 1/8000 of the scene width and your camera has an 8000-pixel-wide sensor. If your camera is aligned perfectly, then all those white square photons fit on one sensor pixel and we see values: 0 0 0 255 0 0 0, right? But if we turn it 1/400th of 1 degree (on a 50mm lens) (inverse tan(18mm/4000/2/50mm)) horizontally and the same vertically, then that white square is now falling on four different pixels, which each only see 1/4 of its photons, a 2-stop reduction. With 16 stops dynamic range, two stops is 1 bit. We'll see 0 0 127 127 0 0 now. Despite our perfect lens, perfect focus, perfectly noise-free sensor, perfectly motionless subject and camera... our MTF falls from 100% to 25% just by changing aim 1/400th of 1 degree. More generally, if the target has squares 1/8000th the width but our sensor has some other width, say 8192 pixels (R5), then no matter how we point the camera, SOME test scene squares will fall perfectly between pixels and only give a 25% MTF.

    So now the crux of my thesis: the movement of a pixel during the correcting distortion, even a LOT of distortion, is actually of no greater magnitude than this perfect shot of a 1-pixel feature, that is nonetheless misaimed by a half pixel.

    At worst.

    It cannot get worse than that.

    It cannot get worse than having a perfect lens, perfect focus, noise-free sensor, zero diffraction, zero movement, and simply being off by half a pixel.

    And that's not just good, or very good, or good enough for me. It's as good as you can hope unless you're shooting only scenes with features that all align with your sensor's pixel grid.

    ---------------

    But again, I may be totally wrong, which is why I want to hear you guys out.

    Do you have an argument or an image showing how the results are actually substantially worse than I'm arguing here?
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  10. I would vote for constant aperture for video and 15mm as starting point would be very welcome, especially with good correction in the distortion department. But maybe two lenses for PHOTO and video + VIDEO and photo :)
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  11. RF-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.
    Me too.
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