Old Man FL/FD said:

I want to make clear my discussion pertains to in-camera lens correction for JPEG output. My attachment sample is for chromatic aberration, but my point also applies to vignetting and geometric distortion.

Canon lens designers, with their Computer Aided Design (CAD) software, know exactly how a theoretical lens design performs regarding various aberrations. The lens design process involves numerous compromises to get to a marketable product.

One important lens design consideration is how easy it is to manufacture. A follow on from this is how consistent is unit to unit performance.

The in-camera lens correction software algorithm uses a ‘model’ of the lens to modify the internal RAW sensor data for JPEG engine output. Any ‘deviation’ of a particular lens being corrected from the model of that lens will result in a sub optimal corrected result.

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This is Digital Lens Optimizer, which is different.

But DLO is pretty damned cool.

Exploreshootshare said:

Less distortion than the RF 50mm F1.2 doesn't mean is doesn't have any. Which is exactly what I stated.

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The RF 50mm f/1.2 L has 0.2% barrel distortion.
The RF 50mm f/1.4 L has a tiny amount of pincushion distortion, probably between 0.2 and 0.1% if measured.
It's a near-zero distortion lens, they both are.

So no, it does not rely on software corrections for distortion, and it has a traditional level of vignette for a f/1.4 lens.

It’s a really nice piece of glass

m4ndr4ke said:

Not, not really. The 50mm VCM has similar levels of vignette as the EF 50mm f/1.4, and less distortion than the RF 50mm f/1.2 L.

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Less distortion than the RF 50mm F1.2 doesn't mean is doesn't have any. Which is exactly what I stated.

neuroanatomist said:

Manly man lenses like the Canon EF 11-24mm f/4 that had manly barrel distortion of 4.5%, or the even more manly manny Sigma 12-24mm f/4 Art with an even more massively manly 5.3% barrel distortion (the same as the Canon RF 14-35 that 'requires' correction, oh my!).

Meh. I'll stay here in the present, thanks.

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The manliest man lens in my collection is a Zeiss 3.5/18mm Distagon - it has a so-called moustache distortion (but only a mild one) ...

Half the people commenting are not realising this thread is about distortion corrections and image stretching, not vignette, it looks like they just skipped Richard’s piece and went straight to the comments section.

For some reason, few users seem to think that EF lenses were some holy grail on vignetting, but they were not. Vignetting is nothing new, many EF lenses had lots of it, some even more than its RF replacements.

A few examples for vignetting, EF vs RF:

roby17269 said:

Does the VCM 50/1.4 require digital corrections to stretch image corners that do not cover the entire sensor? or just some geometry correction and lightening up vignetting?

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Exploreshootshare said:

Yes, it relies on digital correction. Apparently, for distortion it is not as extreme as with other vcm lenses.

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Not, not really. The 50mm VCM has similar levels of vignette as the EF 50mm f/1.4, and less distortion than the RF 50mm f/1.2 L.

roby17269 said:

Does the VCM 50/1.4 require digital corrections to stretch image corners that do not cover the entire sensor? or just some geometry correction and lightening up vignetting?

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Yes, it relies on digital correction. Apparently, for distortion it is not as extreme as with other vcm lenses.

roby17269 said:

or what, should we do away with forum such as CR?

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Noooo! Of course not! But maybe spending less time arguing over - what feels like - endlessly ongoing debates (digital corrections/ dynamic range) and writing/ reading more about we all enjoy, look forward to or just share knowledge about photography. And, of course, guessing and debating new rumors and upcoming camera gear

Quack said:

I would go one step further...

Your entire image with digital cameras is created with a series of digital corrections. Your sensor is not recording the colors as you will see them, they have to go through a demosaicing, in other words a digital correction. The tones from dark to light are not recorded on the sensor as you will see them after converting the RAW image, they need to go through a tonal correction algorithm. Same with White Balance, and many, perhaps most most now apply noise reduction in the RAW conversion. Your RAW file is not a negative. So your converted image is a,series of Digital Corrections. So, why the big deal when it comes to lenses? Makes no sense.

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Except that they're not the same though: most of what you list are consequences of how bayer sensors work. There is no choice apart perhaps for NR applied in camera.
For lenses there are or there could be alternatives.

Software is doing so much work in post anyway for most photographs that it sort of makes sense that we are getting more lens corrections too. Love it or hate it, seems to be the way of the world now.

SirIssacNewton said:

First time seeing a Hermit Thrush, taken with my Canon R10 and RF 100-40

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Nice series. I especially like the 2nd shot.

JustUs7 said:

But that’s where I get confused. It can’t be cropped down to 6000 on the horizontal because there are only 6000 pixels to start. So it has to be cropped to something less than 6000, then stretched, then have the stretched pixels split back so the file shows a full 6000.

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The image is stretched first, and after that stretching it is 4000 pixels high (for the 24 MP sensor in your example) and wider than 6000 pixels.

Look at the area outlined by the red rectangle in the diagram below. Notice how in the uncorrected (left) image there is a region between that rectangle and the edge of the sensor area (magenta). After the distortion is corrected, that portion of the image above and left of the red rectangle is outside the 6000 x 4000 area.



Also note how in the uncorrected image the red rectangle is closer to the top of the frame than to the left edge. Thus, the red rectangle is moved more sideways than up when the image is ‘stretched’. That exemplifies the reason there is ‘excess’ image on the sides that must be cropped away to maintain the 3:2 ratio.

It’s also worth noting that when stating you can obtain an image wider than 6000 pixels, I am talking about processing by DxO. Under the hood, when Canon processes the image (in camera or in DPP) it is still wider and cropped down to 6000 pixels, but there is no way to get that wider image out of the camera/software.

scyrene said:

I'm just curious how vignetting ruined landscape shots. Apart from the astro landscape niche discussed at length on other threads, my understanding is most landscapes shots are taken stopped well down - regardless of the lens used - so vignetting shouldn't be an issue?

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The one coming to mind most affected was a time laps video of a sunset I shot on a Z9 with a 15-35 f4 S lens. The sky was bright orange and purple and the corners on that lens get booster 4-5 stops.. the noise in the corners was wild.

First time seeing a Hermit Thrush, taken with my Canon R10 and RF 100-400

Nice, informative writeup. Thanks

Beautiful shot. Clear view of the subject. Nicely done!

I'm glad to see some quantitative data on corner stretching. So for the 14-35 at 14 mm, the amount of distortion is 5.3%. This results in a reduction of extreme corner resolution by 10.6%. I wonder if we can use a rule-of-thumb whereby the corner resolution decrease is about twice the distortion amount.

Yes, 10.6% may seem like a hefty penalty. But I think of it this way. I picture a Canon engineer working with modeling software. Suppose that a base design can be tweaked in two directions: one with heavy barrel distortion and a high corner resolution (say 4150 lp, for argument's sake); or one with low distortion and a much lower native resolution (say 3500 lp). Even after geometric correction, the lens with barrel distortion is still the clear winner.

There is one bit that causes me hesitation. The comparison is between corner resolutions. However, the uncorrected corner resolution was not meant to ever be used. It is meant to be cropped away. A fairer comparison would be the resolution of the same part of the image, which for the uncorrected version would lie a bit closer to the center of the image. A nitpick - yes. But possibly relevant.

Which leads me to the opticallimits reviews. Why are they still so obsessed with uncorrected images? Why are they measuring vignetting of uncorrected images? to me this is a bit like slapping an APSC lens on a full-frame body and then complaining about corner resolution. The uncorrected corners simply aren't meant to be used. And if you do use them, it's at your own peril. This is off-label use.

neuroanatomist said:

In the case of a 24 MP sensor, it’s cropped down to 6000 pixels wide.

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But that’s where I get confused. It can’t be cropped down to 6000 on the horizontal because there are only 6000 pixels to start. So it has to be cropped to something less than 6000, then stretched, then have the stretched pixels split back so the file shows a full 6000.

Quack said:

I would go one step further...

Your entire image with digital cameras is created with a series of digital corrections. Your sensor is not recording the colors as you will see them, they have to go through a demosaicing, in other words a digital correction. The tones from dark to light are not recorded on the sensor as you will see them after converting the RAW image, they need to go through a tonal correction algorithm. Same with White Balance, and many, perhaps most most now apply noise reduction in the RAW conversion. Your RAW file is not a negative. So your converted image is a,series of Digital Corrections. So, why the big deal when it comes to lenses? Makes no sense.

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To take it one additional step further...
What about perspective, vignetting, exposure and cropping corrections applied in darkrooms in film era?
Was it a form of noble creativity because it was done by hand?

mb66energy said:

The choice of my examples is not great, here you are right,, long focal lengths are easyer to correct - So lets think about 18mm f/4.5: I would not accept the need of digital correction. For a compact 15mm f/2 I would accept moderate digital correction.

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Maybe just skip the examples. What would even be the point of an 18/4.5 lens? But I get your point. I’d say it’s a factor for those who care about it. I suspect more people would choose the benefits of lenses designed with digital correction required, e.g., potentially smaller, lighter, and/or cheaper, over the debatable drawbacks. I use the word debatable because if an image has similar IQ after digital correction as it would be from an optically corrected lens, the drawback is entirely mental.

mb66energy said:

About filling the image: this is in my opinion a consequence of correcting strong distortions which is the primary goal of digital corrections.

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They go hand in hand. If a lens is designed with an image circle smaller that doesn’t completely cover the sensor, then the designers are incorporating the need for correction to fill the corners into the design.

You can see that from the MTF charts that Canon publishes. For example, the RF 14/1.4 has an image height (i.e., image circle radius) of 18.68mm and that is short of the 21.64mm image height of the FF sensor. The X-axis of an MTF chart is distance along the ‘diagonal’ (the radius from the center to the corner of the sensor), and if distortion correction was not incorporated into the MTF charts then the lines would stop before the right side of the plot (at 18.68mm in the case of the 14/1.4). But they don’t.

Malm said:

And I thought that these 'digital correction' allows for a better image quality as most writers assume. And now I can only use these expensive 'digital correction' lenses after stopping down?? That doesn't make sense!

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I'm just curious how vignetting ruined landscape shots. Apart from the astro landscape niche discussed at length on other threads, my understanding is most landscapes shots are taken stopped well down - regardless of the lens used - so vignetting shouldn't be an issue?

Spring is trying to spring here in the midwest USA, but cold temps return this weekend.

Nice temps today, and the (sort of) trilling of the male Carolina Wren is a sign that warmer weather isn't far off.

R5II + 200-800; ISO 800

neuroanatomist said:

The types of corrections being discussed here result from the image circle being smaller than the sensor. Notice how we're talking about lenses like the RF 14/1.4, the RF 14-35/4, etc. With telephoto lenses, that typically does not happen so your proposals of 150-180mm lenses with a 'need for correction' is a red herring. They won't need it. Even a correction-requiring lens like the RF 24-105/2.8L Z covers the full image circle by 28mm, it's only at the very wide end that it needs digital correction to fill the corners.

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The choice of my examples is not great, here you are right,, long focal lengths are easyer to correct - So lets think about 18mm f/4.5: I would not accept the need of digital correction. For a compact 15mm f/2 I would accept moderate digital correction.

About filling the image: this is in my opinion a consequence of correcting strong distortions which is the primary goal of digital corrections.
By the way the RF 24 105 Z lens has surprisingly strong pin cushion distortion at the long end too but that is a design choice of Canon outsourcing distortion correction to the image processing ... but that's a zoom specific compromise, I think.

Del Paso said:

That's absolutely right. As you wrote, in film times, optical correction was a necessity, lens manufacturers didn't have a choice.
Yet, when I see how good the VCM lenses have become, "despite" software correction, I wonder how long the debate optical vs. software can still go on...

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I guess the progress in computer based design, new optical materials and coatings will go hand in hand with a deeper digital correction, and users will definitely profit from that progress.

Del Paso said:

Rejecting software correction implies rejecting also DXO, LR etc… editing.
What matters is how good the picture you obtain is, whether optically or electronically corrected. Period!

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I would go one step further...

Your entire image with digital cameras is created with a series of digital corrections. Your sensor is not recording the colors as you will see them, they have to go through a demosaicing, in other words a digital correction. The tones from dark to light are not recorded on the sensor as you will see them after converting the RAW image, they need to go through a tonal correction algorithm. Same with White Balance, and many, perhaps most most now apply noise reduction in the RAW conversion. Your RAW file is not a negative. So your converted image is a,series of Digital Corrections. So, why the big deal when it comes to lenses? Makes no sense.

My take, Canon is trolling us, knowing someone would take a pic, but just using an R1 casing for testing out features for future cameras in general, not the R3 II specifically. No way the R3 is going to have all those features and cannibalize the bodies above and below it. I'm really dubious of any R3 II though.

Malm said:

And I thought that these 'digital correction' allows for a better image quality as most writers assume. And now I can only use these expensive 'digital correction' lenses only after stopping down?? That doesn't makes sense!

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Yes, what you say makes no sense.

I’m not sure who is saying the image quality is better, there is a difference between better and not worse. Yes, in some cases it is better and in others, it is worse. It depends on the lens. In most cases, the difference is probably not enough to have a meaningful effect, at least in most use cases.

No one is forcing you to use any particular aperture. As I pointed out, there are ‘optically corrected’ EF mount lenses with >5% distortion and/or >4 stops of vignetting. No one forces users of those lenses to only use them zoomed out or stopped down.

But…straw men are fun to stand up, right?