02-06-2015, 09:33 PM
Quote:Basically you're right, dave9t5. I'm just not sure if that rule is valid for those FLs, because they have to do tricks to get that "impossible" FL - distance between sensor and rear element on a FF DSLR never is less than 40 mm. So each lens with an FL below those 40 mm needs some extra elements. 11 mm / 4 is a diameter of 2.75 mm and that is "aperture wide open". I'm sure, Scythels could elaborate on this and I'm also sure I wouldn't understand and mumble something like "pretty amazing".
Yep, that's why I mentioned that I'm not Scythels, ha ha.
It's a rule of thumb that I used and probably breaks down on extreme lenses like this one.
On the other hand, this is a huge lens for f/4 so I can't imagine an f/2.8 construction would be anything less than unmanageable huge.
The retrofocus construction is an inverted telephoto. I wonder what the equivalent (size) f/4 telephoto lens would be for an 11mm retrofocus?