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Canon RF 20mm F1.4L VCM MTF Analysis and Comparisions
Looking at the Canon RF 20mm F1.4L VCM, and from first glance, I'll save you the trouble of reading everything I'm going to write - this is possibly the finest 20mm prime lens that Canon has ever developed.
Hyperbole, perhaps, but I've never seen an MTF so good on anything other than a Canon prime lens of longer focal lengths. This is an absolute no-compromises prime lens from Canon, with every coating that Canon has ever developed in it, including a BR coating.
For the sake of comparison from the 10,000-foot level, the MTF resolution and contrast should be almost identical to that of the 24mm, with the exception of it being 4mm wider.
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Canon RF 20mm F1.4L VCM MTF Summary
Here's the MTF from Canon Japan showing the 20mm lens.
Astimatism and Coma
What strikes me is that the sagittal and tangential lines are very close to each other for resolution and contrast nearly out to the periphery of the lens. This lens should, at first glance and without any empirical testing, be very good in terms of coma performance as it has low astigmatism—one of the lowest I've seen from a Canon fast prime.
The Canon RF 24mm F1.4 VCM had very low coma, and this lens should have even less, making it arguably one of the best astrophotography lenses Canon has developed—assuming the lens performance matches Canon's computed MTF.
We'll have to wait until we see actual, real-world results, but this lens should be excellent at first glance.
Resolution and Contrast
By all accounts, this lens matches up with the other ultra-wide lens, the RF 24mm F1.4 VCM, in terms of resolution and contrast, so much so that I had to quickly glance back and forth to ensure the MTF charts were different.
As you can see, the MTFs of the Canon RF 24mm F1.4L VCM and the Canon RF 20mm F1.4L VCM closely match, but the Canon RF 20mm has slightly less astigmatism. They are close enough that mere mortals will never be able to tell them apart in the real world.
It is pretty crazy that Canon managed to match the performance while making the new Canon RF 20mm 4mm wider in focal length.
Summary
Like the Canon RF 24mm F1.4L VCM, this lens is the best in class and better than anything Canon has developed before. There was a time when we used to adapt the Zeiss 21mm lens to the Canon EF lens because Canon simply had no good ultra-wide primes.
That time is long forgotten, and I wouldn't be surprised if this lens gives the legendary Zeiss lens a run for its money, even though this Canon lens is over a stop faster.