ExplicitSnow wrote in post #16052865
reason for the question...it was a simple thought that popped in my head randomly the other night...thanks
Look at it like this. There is a reason why fast lenses have large objective elements. It's to let in more light. Compare a set of good night binoculars to a standard pair. The objective end is huge so that they gather more light to allow you to see at night, even under starlight. Look at the size of the 17-55 vs. the 18-55. That added size is what is needed to bring in an additional stop of light. The extra 1 mm of field is a slight factor, but most of the difference in the objective end of the lens is for light gathering. Even if you could make the blades fit in the 18-55 (no way, but if you could), it wouldn't make a bit of difference in the speed of the lens.