How it do dat? Wind evenly, that is.

[wilhelm]

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?

[john_collier]

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.

 

<p>

 

Cheers

 

<p>

 

PS I am visiting with my parents so you can temporarily contact me at

rcollier@look.ca

[wilhelm]

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!

[msitaraman]

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...

[Rob F.]

Clever, these Germans!

[ron_gregorio]

Ja.

[richard_oleson]

It's not just the Germans, actually ... every 35mm camera does the

same thing. I suppose Leica may have been the first though.

 

<p>

 

:)=

[wilhelm]

I guess they'd been doing it in movie cameras for 30 years before the

Leica. Thanks, Tom Edison.