Thanks Neuro: Does it mean that the 70-200 mk.ii could possibly do 70mm @ f/0.98 ? (200/2.8 = 71.4, and 70/ 71.4 = 0.98) Since the lens element is large enough? So the lens potentially could be a Variable 70-200 f/0.98 -2.8L ? If they so chose to build it with similar glass elements?
Chuck Westfall answers that in the link above (the answer is 'no', BTW).
What Chuck seems to be saying is that they design it this way. Not sure it fully answers my question. Chuck is saying that the Iris changes (becomes larger when you zoom to 200mm) .... well don't make it go larger, just let it sit there at 71mm when we zoom at 70mm, not make it go smaller when we go to 70mm. I am sure it is not that simple as i made it out... but I am curious what happens if they do not vary the "virtual" iris at all?
Agreed, I read Westfall's response and I don't think he ever answers the question. He "explains" how constant aperture lenses work – sort of; but he doesn't answer the question posed to him, which seems to be: why not a variable aperture lens with 2.8 at the long end and f1 at the short end.
I deleted my post since I was not sure if i would get hammered for questioning Chuck... I remain unsure though. It seems they are playing with the definition of the aperture/ F-Stop conventions. In this case with the aperture being behind what he called the tele-converter, does not play with the classical definition of the F-Stop as it applies to irises and the aperture being up front...