<li>When doubled, twice the lateral aberration, longitudinal aberration is 4 times greater rate of expansion, because the F-number is also double, longitudinal aberration is twice per depth of focus</li>
I read that as it, like the 2X, adds two stops. So a 2.8 lens -> 5.6, not 8.
Unless Canon have found make a teleconverter that opens the aperture wider, I don't see how the teleconverter could multiply the focal length by 2.8 without (relatively) closing the aperture by three stops.
Maybe they designed it in such a way that it magnifies the apparent aperture (kinda like how constant f zooms work).
Dunno, just speculating based on that single bullet point. What else would it mean?
It may not affect any current lens which it is attached to, as simply increasing f number accordingly by 3 stops. Apperture number comes from dividing focal length by real hole size. If focal length increases I don't see a way to increase the attached lens apperture hole.
A 70-200 f/2.8 at 70mm has a maximum opening 25mm in diameter, agree?
A 70-200 f/2.8 at 200mm has a maximum opening... 25mm in diameter.
AFAIK, there's no physical mechanism opening the blades wider as the focal length increases. Rather, the zooming in optically magnifies that 25mm aperture such that it appears to be 71mm in diameter (at the 200mm example).
I see no reason they couldn't employ that principle in teleconverters.
That said, sure, I probably I read it wrong, hence me asking what they meant by that bullet point.