02-06-2015, 08:28 PM
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".