The RF mount has seen some extreme lens designs, with Canon pushing into new territory with options like the revered 28-70mm f/2L. It seems they have no intention of slowing down, as another interesting design has emerged, this time one sure to please sports and wildlife photographers.
A recent Canon patent has emerged for an RF 100-300mm f/2.8 1.4x Extender lens. While such a lens is not unheard of, as both Nikon and Sigma make 120-300mm f/2.8 lenses, this would be the first such full frame with a built-in teleconverter, which would effectively make it a 140-420 f/4 lens when engaged.
I do wonder if this is why we have not yet seen an RF 300mm f/2.8 lens, as Canon may be exploring the idea of replacing it with a lens such as this. That being said, just because a patent appears, it does not mean the product will eventually be brought to market, but I am confident we will see some sort of 300mm f/2.8 lens for the RF mount eventually, whether a prime or a zoom.
Having owned and used the Sigma 120-300mm f/2.8 for several years, I can say it is a tremendously versatile and useful lens, and I wouldn't be surprised if Canon chose to go the zoom route to fill out the shorter supertelephoto focal lengths. I suspect such a lens would be quite popular. Hopefully, we will hear more soon!
140mm - 420mm would be pretty wild. I wonder if you can turn off the teleconverter and use the 2.8 lens at the shorter focal length or if it's always having to run through the glass?
Yes, it could be used with the TC engaged or not engaged, just like the EF 200-400mm f/4 w/1.4 TC that makes it a 280-560/5.6 when engaged and a 200-400/4 when bypassed.
If you think that Canon will replace fast prime with zoom lens then you don't know canon at all. One of the mine reasons Canon doesn't want to give out RF mount to sigma, Tamron and other third party companies is mainly because they won't be able to keep up with the focusing speeds of the latest cameras.. It was always the case with DSLR and it will be even harder for them now even if they try to reverse engineer RF mount like they did with EF. Still waiting for the RF 70-135/2.0 L rumored in 2020
I've used the Sigma 120-300/2.8 for a couple of football seasons. It's OK, but I'm still not fully convinced it does any better than cropping shots taken with my 70-200mm f/2.8 L II IS to the 300mm FoV. This is with both a 5DIV and a 7DII.
100-420mm f2.8/f4 would be pretty awesome.
It would be my choice over a fixed 300mm prime any day for the versatility the fixed 300mm would lack. And knowing Canon there will be no loss in IQ with such a lens.
100-300/420 f/2.8/4? Shut up and take my money. I'd consider trading in both my 70-200 and 100-500 for it.