The correct lens for the transparent is a real 24mm but has the word “DUMMY” stamped on the lower barrel. This lens is very hard to find but I’ve managed to track a couple down!
The serial numbers so far are 1291387 and 2026618 which suggests that the transparents were made throughout production. A collector in Germany has a DUMMY No. 2024965.
If you have a DUMMY then please email me with the serial number, thanks. firstname.lastname@example.org