Do we know that the RF 100-500 has the same filter size as the EF 100-400? I was suggesting it looked narrower to me, so not only could it not be f/6.3 at 500mm, but I was speculating that it's a narrower aperture than f/5.6 at 400mm also.
Although a Canon user and fan I have to say that these f/6.3 3rd party lens users enjoy 600mm instead of 500mm and this is a significant difference.
Agreed. Not necessarily 5.6 at 400, but I'll wager that when you have an established and successful multi-generation 100-400mm design that gives 5.6 at 400, all the designer basically (simplistically) needs to do it to make a telescoping tube a little longer and pull the objective lens a little father forward to get to 500mm. Honestly, if we took apart a 100-400 and just held the front element a little father forward, it would presumably image as a 500.
Granted, lens design has subtleties, and there would presumably be issues introduced (possible mechanical getting that telescope distance - I'd cringe at a three-part telescope). But it's hard to imagine that the change would require reducing the aperture at 400mm. That's the last solution the designer would be allowed by the boss to revert to.
As an aside, one hopes that the RF mount enables other benefits in image quality and product configuration. I now assume that the magnificent RF 70-200 that won me over to Canon late last year was essentially the 100-400 adapted to those specs.
The more I read, I really believe the 100-500 is the RF equivalent of the EF 100-400 II. The IQ of 400-500 should be better than a 100-400 II + 1.4x TC II since the lens is engineered to reach that length without the additional elements in a teleconverter. I actually thought we would see an RF 70-400 (pickup on the short end), but hey surprised me going the other direction. The RF 100-500 fills that general purpose long telephoto range. I do not think we will see a RF 70-400 or RF 100-400. This leaves an opening for Canon to deliver a higher end 200-600 f5.6 or f6.3 focused on sport and wildlife photographers - somewhere between the 100-500 and big whites. I don't know if this is sound logic or wistful thinking.
Yeah, with 45Mp sensor you shoot at F5.6 with 100-400 lens and then crop to 500mm for framing. A stop of light can be a big deal if you are ISO limited already at F5.6Seriously? Somehow everybody is fine with the 100–400mm with 1.4x at f/8 but the same lens with a "1.25x" builtin extender that you don't even have to toggle on and off is somehow "not L"? Sheesh…
The only reason f/5.6 was the limit for so long was that DSLRs could not focus reliably much beyond that. But DPAF can focus down to f/11, and at the same time sensors and IS systems are better than ever. There's absolutely no reason to artificially limit engineers by imposing an arbitrary f/5.6 max aperture limit.