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Loswr
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Perhaps you misread what I stated, which was that increased noise from vignetting correction and loss of sharpness from distortion correction apply to ALL lenses (unless there is no need for those corrections in the first place, which would only apply to theoretically perfect lenses that don't exist). That's not false, that's fact.
This is pretty simple. All real lenses have some optical aberrations, practical considerations ensure that is the case. My Zeiss microscope objectives costing far more than the R1 still need significant flat field correction for tiling images (i.e., they have vignetting). At issue is the degree of correction required, and that is inherent to the design of the lens.
Many UWA zooms in older mounts have severe distortion. The EF 11-24/4L has >7% barrel distortion at 11mm – it fills the frame without correction, but barely. The RF 14-35/4 has a bit over 10% barrel distortion at 14mm, IIRC, and it doesn't quite fill the frame. Both of them 'need' correction, and the effect of the correction is the same, loss of corner sharpness.
Mirrorless lenses (not just Canon's RF) leverage the fact that the only way to view the output is digitally to enable the manufacturers to make design tradeoffs allowing aberrations of greater magnitude, but qualitatively they are the same. The RF 15-35/2.8 has relatively little distortion (around 1%) but strong vignetting (5 stops), whereas the RF 14-35/4 has far more barrel distortion but only about 2.5 stops of vignetting.
I'd argue that it doesn't matter for any of the lenses in general use. Except in some people's minds.
Again, but by that logic there is no such thing as an optically corrected lens, except the aforementioned theoretical ones. But the point was that the EF 35/1.4L II does not force correction of distortion, but it still has the same amount of vignetting as the RF 35/1.4 that does force those corrections. The 5 stops of the RF 15-35/2.8 illustrate that concept even more effectively.
The context here is wide angle, rectilinear lenses. Show me one of those that doesn't have at least some residual distortion. Theoretical lenses need not apply. Sure, a lens design where there is no distortion to correct (e.g. not-too-fast short telephoto lens, or a zoom lens at the transition from barrel to pincushion assuming no mustache distortion is present) are not going to 'smear' because there's nothing to correct.
Agree that no direct single lens comparison is possible. But looking across the range of EF and RF lenses, the gestalt conclusion is that they're the equivalent. The digitally corrected lenses don't have consistently better or worse corner sharpness than the lenses not requiring correction.
Those who decry forced correction of distortion claim that it is inherently worse. My point is that it is not.
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I was mostly with you till this heretical assertion 
