After fifty years I suddenly realized that although the takeup knob turns exactly one turn per picture (IIIf), and the toothed wheel moves exactly 8 perforations so that there is precisely the same internegative spacing, the film wound around the takeup spool gets bigger and bigger, which should require less turning of the takeup knob. But it don't. How it do dat?

-- Bill Mitchell (bmitch@home.com), December 25, 2000

Answers

The winding mechanism and advances the film by turning the sprockets a fixed amount(also recocks the shutter and advances the counter). This ensures that the spacing is always the same. The take-up spool is driven by a slip clutch mechanism that "slips" more and more as the film diameter on the take-up gets bigger. You can test this by turning the take-up spool, when it is in the camera without film, with your finger. It turns with a resistance. This resistance you feel is the slip clutch working.

Cheers

PS I am visiting with my parents so you can temporarily contact me at rcollier@look.ca

-- John Collier (jbcollier@home.com), December 25, 2000.

Thanks. I can't tell any difference in resistance between an empty camera and the 36th exposure. The slip clutch mechanism must be a hum-dinger. Here's to Oskar Barnack!

-- Bill Mitchell (bmitch@home.com), December 25, 2000.

Bill: Thanks for asking a question I remember wondering about often, 35 years ago, after observing a Contax IIa. The long-term has its rewards...

-- Mani Sitaraman (bindumani@pacific.net.sg), December 25, 2000.

Clever, these Germans!

-- Bob Fleischman (RFXMAIL@prodigy.net), December 26, 2000.

Ja.

-- Ron Gregorio (gregorio@ksc.th.com), December 27, 2000.

It's not just the Germans, actually ... every 35mm camera does the same thing. I suppose Leica may have been the first though.

:)=

-- Rick Oleson (rick_oleson@yahoo.com), December 27, 2000.

I guess they'd been doing it in movie cameras for 30 years before the Leica. Thanks, Tom Edison.

-- Bill Mitchell (bmitch@home.com), December 27, 2000.