It looks like Canon is indeed working on their RF mount super telephoto optical formulas. We were told a couple of days ago that an RF 500mm f/4L IS would be the first super telephoto lens launched for the EOS R system.
A USPTO patent has appeared that shows optical designs for an RF 400mm f/2.8L IS, RF 500mm f/4L IS and an RF 600mm f/4L IS.
Canon RF 400mm f/2.8L IS USM
Focal length: 392mm
F number: 2.9
Angle of view: 3.16°
Image height: 21.64mm
Entire lens length: 360mm
Backfocus: 31mm
Canon RF 500mm f/4L IS USM
Focal length: 490mm
F number: 4.12
Angle of view: 2.53°
Image height: 21.64mm
Entire lens length: 412mm
Backfocus: 33mm
Canon RF 600mm f/4L IS USM
Focal length: 588mm
F number: 4.12
Angle of view: 2.11°
Image height: 21.64mm
Entire lens length: 476mm
Backfocus: 33mm
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