Opinion: Love it or Hate it, Digital Correction is here to Stay

[Richard-CN]

OpticalLimits has recently gotten its hands on the Canon RF 14-35mm f/4L IS USM, which was announced way back on June 29, 2021. That in itself probably isn't newsworthy. So instead of talking about the review itself, I focused on a specific part of the review that caught my eye. This part of the review […]

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[m4ndr4ke]

Oh boy, I'm anticipating the comments


What strikes me the most is the fact that both lenses show essentially the same profile in the corners. If the loss on image quality was significant, we would see the 14-35mm f/4 falling at the end of the line, which we don't.

 

[Del Paso]

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!

 

[Rafał]

You missed the point that optical correction of distortion is not free - it also introduces aberations and losses in quality. There was an interview with Sigma engineers who said that in many cases correcting distortion and vignetting digitally results in better sharpness than doing it optically.

 

[Klendothir]

I had both the 15-35 and the 14-35. I finally sold the 15-35 last week because it constantly stayed at home. The 14-35 is so much smaller, lighter AND a full mm wider where it really counts. I can definitely live with one stop less light at these lengths. In the worst case, I can crank up the ISOs (I use DxO PhotoLab anyway) And while I also have the 10-20, this one often feels too wide.. The 14-35 barely leaves my camera during a city trip.

 

[Richard-CN]

Oh boy, I'm anticipating the comments

Darn right! I live for it.

 

[Richard-CN]

You missed the point that optical correction of distortion is not free - it also introduces aberations and losses in quality. There was an interview with Sigma engineers who said that in many cases correcting distortion and vignetting digitally results in better sharpness than doing it optically.

That's a fair point. I implied it, that by not worrying about the image circle as much, it allows the designers to focus on other aspects of the design, but yes, I didn't go into as much detail as I should have.

 

[AlanF]

OpticalLimits has recently gotten its hands on the Canon RF 14-35mm f/4L IS USM, which was announced way back on June 29, 2021. That in itself probably isn't newsworthy. So instead of talking about the review itself, I focused on a specific part of the review that caught my eye. This part of the review […]

See full article...

Great analysis Richard! Go one stage further and compare the two lenses at 18mm, 24mm and 35mm at f/4, and you see from the optical limits charts that the 14-35mm has far, far less fall off on going from the centre to the extremes. So, for this pair of lenses, the optical correction at the shortest length causes far more damage at longer lengths than does the digital!

 

[Richard-CN]

Great analysis Richard! Go one stage further and compare the two lenses at 18mm, 24mm and 35mm at f/4, and you see from the optical limits charts that the 14-35mm has far, far less fall off on going from the centre to the extremes. So, for this pair of lenses, the optical correction at the shortest length causes far more damage at longer lengths than does the digital!

That's true, and it's much harder to get to 14mm as well in terms of optical design. The 14-35 has a slightly more zoom range, and because it's software reliant, the designers can engineer a better-performing lens overall.

 

[el peso]

Whenever digital correction in modern lenses is discussed, I’m reminded of a comment by Ryan Carnathan of The-Digital-Picture in his review of the Canon RF 14–35mm F4 L IS USM lens:

Does the strong distortion correction matter? Psychologically it does, and an image captured from a non-distorted lens can similarly be up-sized to even higher resolution using AI, potentially giving it an advantage. That said, did you notice any corner issues until this point in the review? Likely not substantial ones.

 

[Skyfall]

I had both the 15-35 and the 14-35. I finally sold the 15-35 last week because it constantly stayed at home. The 14-35 is so much smaller, lighter AND a full mm wider where it really counts. I can definitely live with one stop less light at these lengths. In the worst case, I can crank up the ISOs (I use DxO PhotoLab anyway) And while I also have the 10-20, this one often feels too wide.. The 14-35 barely leaves my camera during a city trip.

I agree, was my only lens on a 3 week hiking trip in the alpes last summer. The only thing i missed was a tele lens for the occassional wildlife. It is also good enough for auroras and okay for wide field astro, especially because of the convenience of having one lens. Now i am considering the 20mm for handheld astro/auroras but is not sure if its wide enough. Would love a third party manual in the 14-18 range with f2 or something

 

[Del Paso]

Great analysis Richard! Go one stage further and compare the two lenses at 18mm, 24mm and 35mm at f/4, and you see from the optical limits charts that the 14-35mm has far, far less fall off on going from the centre to the extremes. So, for this pair of lenses, the optical correction at the shortest length causes far more damage at longer lengths than does the digital!

While in my "physical" comparison, the 15-35 was noticeably better at 35mm, and at least as good at the other focal lengths...

 

[AlanF]

While in "physical" my comparison, the 15-35 was noticeably better at 35mm, and at least as good at the other focal lengths...

Centre or edges?

 

[sturm3n]

You missed the point that optical correction of distortion is not free - it also introduces aberations and losses in quality. There was an interview with Sigma engineers who said that in many cases correcting distortion and vignetting digitally results in better sharpness than doing it optically.

I’d love to learn more about this; do you have links to those interviews?

 

[GMCPhotographics]

The Digital corner profiling discussion is as complex as the use multitude of case scenarios from the users who shoot with these lenses.
If the corners are software re-generated using AI then there is no loss of detail or Dynamic range. You should be able to push the exposures and oggle the fine detail in the corners and be happy with the results. HOWEVER.....Canon doesn't employ AI software based corner regeneration, what they do is stretch the corners and use the raw file's DR to bump the corner exposure to that of a perfect lens. This is fine if you don't mind loosing a little bit of resolution, maybe even a bit of focal length and a lot of corner DR.
Most Canon UWA lenses already give us a slightly wider angle of view to their acclaimed wide focal length marking. So a RF 14-35 F4L lens is closer to 13.5mm when uncorrected, the focal value of the lens corresponds to the corrected focal length. Another example of this is the sublime RF10-20mm f4L, it's notably wider when uncorrected. So if you take the uncorrected RAW image and run it though software that can AI regenerate the corners, you get an even wider angle of view than the stock lens with Canon correction applied.

Where the non AI software corner correction falls down is in low light landscapes where the rest of the scene is within the reasonable DR range of the sensor. The corners may have been pulled by the profile before you even start to post process the image. If you shoot on a tripod at 100 iso for a super clean image, the far corners might already be at 1600iso noise levels becuase of the correction profile. Once you pull the shadow details a bit (say two stops) the majority of the image will have super low noise at an equivelent of 400 iso...nice and clean. But these far corners will have an equivelent iso value of 6400 and will have a noticable amount of noise compared to the rest of the image. That's just a 2 stop pull. Ok you have AI noise correction, but this approach from Canon does introduce more work for lanscapers. Even a neat 100iso image will have grainy corners, you would need to stack multiple exposure blends to nullify the issue.
Or you crop the bat-sh1t crazy corners out...or use AI generation for the corner fills. It's the penalty for smaller and lighter lenses like the EF 10-20mm f4L.

 

[GMCPhotographics]

You missed the point that optical correction of distortion is not free - it also introduces aberations and losses in quality. There was an interview with Sigma engineers who said that in many cases correcting distortion and vignetting digitally results in better sharpness than doing it optically.

Fixing corner vignetting due to optical shading is not easily "fixed" with a profile. I fthe profile is AI powered then it can clean the iso noise and re-generate the missing details. But a simple mathmatical corner stretch and then applying 4.5 stop white circle overlay over the far corners is only going to add 4.5 stops of noise in the corners to your raw file. Shoot your Raw landscape at say 400 iso, your corners are already profiled at 6400+ iso before you even start your post prod on the image. There's no magic bullet with camera generated lens profiles.

 

[blackcoffee17]

Im fine with digital corrections as long as large portions of the image are not replaced by AI generated data.

 

[blackcoffee17]

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!

It has to be a limit though. Some vignetting and distortion correction is acceptable but i hope we won't see 20% of the sensor area replaced by AI generated image data because the final image is still "good".

 

[Del Paso]

Centre or edges?

Edges! By the way, even TDP's Brian noticed some 14-35 sample variations which he kept mentioned for a short lapse of time on the lens' page.
Especially when using my favourite focal length, 35mm, I pay attention to obtaining the sharpest corners possible. When travelling. I don't use primes, but a 35mm TSE would be for me an instant buy.

 

[Zadak]

If people don't want digital corrections they should just use film cameras ( ͡° ͜ʖ ͡°)