I went to Barnes & Noble today and saw the Imatest numbers for the Canon RF100-500mm lens in the British Canon magazine. The center is 2000 and slightly over and 1500 there-abouts for the edges @500. These are the highest numbers I have seen for any long tele-zoom by about 15% ! - and, the 100-500 does NOT contain any Fluorite or aspherical elements ! - Is it worth about $400 more than the 100-400 with adapter ?? Suffice it to say that compared to the 100-400 w/1.4X (560mm) @ f8 the 100-500 @500 f7.1 sounds pretty good with higher optical performance to boot.
For old schoolers like me, the 7.1 aperture is still a tough pill to swallow tho.
Rockwell's review - https://www.kenrockwell.com/canon/eos-r/lenses/100-500mm.htm
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