305mm Graphic Kowa convertibility question

[Michael Nagl]

Dear Colleagues,

I have just bought a 305mm/f:9 Graphic Kowa - which allegedly equals a Computar - on the *bay, and as the lens is in a barrel, I´ll get a shutter from SK Grimes. Now here´s what I want to know: I´ve read somewhere on this forum that this lens can be converted into a 537mm by using the rear element only - now, this would make a second aperture scale necessary. Can any of you provide me any information what this scale would look like, what value it would start with etc. A picture would be most helpful.

Thanks in advance for your competent advice
Michael

[EdWorkman]

305/9= 34
537/34=16
in round numbers