John, the goggles for the DR Summicron 50 is a quite different situation. And you're right; the lens is normally used without them, and the goggles are put on when you want to focus closer... Thus the term "dual range".
For the several 35mm lenses that were offered in goggled form, this was specifically for the M3 camera, which didn't have native 35mm framelines; the widest is 50mm. So these goggles "demagnify" the finder in such a way that the 35mm field of view appears within those 50mm framelines. The lens, then, brings up the 50mm framelines when mounted, the goggles are not easily removable, meant to be left on always, and the optical properties of the goggles are such that if they were removed the RF would misfocus the lens.
As it happens, the goggled 35mm lenses work fine on other M cameras too, expanding the view of the 50mm framelines to show 35mm. I like this effect on my M2, whose in-built 35mm framelines are so far out at the edge of the view that I can only see the ends simultaneously in peripheral vision. The 50mm frame is easy to see, so with the goggled lens that frame shows me the 35mm field, I can easily see all around the outside of it, making it much more pleasant to use.
