I agree, it isn't Helvetica, plus Helvetica is a new type face, or at least when the lens in question was being manufactured. It looks to be a bit of a mixture, really. A strong possibility may be that it stems from Germany, or at least partly. Whilst not Bauhaus by a long shot, there were many type faces based on Bauhaus altered enough to be almost different, yet seeming able to hold onto it's core base while at the same time looking very different.
My bet is that the particular letters were a design brief to a graphic artist to come up with something different. As such, they may possibly be slight alterations to an existing type face. Working in advertising in another life, I lived through the type face explosion of the seventies and eighties. In that period, starting in the sixties, fonts were altered sometimes so much one could have great difficulty determining just where they came from. We had a book with close to 3,000 fonts from about 250 typefaces (font families if you will). It was sometimes bewildering when you knew what you were looking for, but flipped pages and pages trying to determine just exactly what it was.
Very nice lettering though, almost worth buying the camera just for that alone!
Mick.