Zeiss Jena aperture ring lever & sprocket ????

[daveleo]

Let me display my ignorance .....
I just bought this CZJena 35mm/f2.8 lens (have not received it yet). This was an emotional purchase with very little research on my part.
Note the lever that appears attached to the aperture ring, and has a metal sprocket that maybe (?) engages with the teeth on the aperture ring.
If the sprocket were not there, I'd guess it's simply a lever to help set the very thin aperture ring. But the sprocket has me baffled. What does it do and how does it work?
I note the pin (axle) of the sprocket is drilled out. Why?
Thanks, as always, for your help.
.

 

[sevo]

That is a Exakta mount lens, and that is its aperture stop-down tab - the Exakta had no camera side stop-down mechanism, it is entirely lens-side. The knob in the middle is the sprung release button, which closes the aperture before the pressure is forwarded to the release knob on the camera front. The serrated ring around the release button does not engage to the aperture ring, but turns by 90° to push the release knob half way, stopping down the lens for long time exposures. The "drilled-out" bit is the cable release socket...

http://www.wrotniak.net/photo/exakta/lenses.html contains a picture that shows the wide variety of stop-down mechanisms on Exakta lenses...

 

[Sarcophilus Harrisii]

I've got a zebra version of the Flektogon in M42 mount. It focuses very close. If you set the focus to infinity and the aperture to f/2.8, you'll notice that as you rotate the focus in to the minimum distance, the aperture ring will close down slightly to reflect the additional exposure dictated by the lens extension. It's neat. Decent performer for its day, too. Do you have an Exakta to fit it to? I recommend the Varex/VX IIa. Last of the really pretty ones (though later models with black badge are not unattractive).

Alpa reflexes used a variation of the Exakta aperture actuating and shutter release system, but on the more conventional front right hand side of the body.
Cheers,
Brett

 

[daveleo]

Thank you for your replies. They are most helpful. The *wrotniak link is excellent* !

I am in the hobby now of collecting and using old lenses adapted to my digital cameras.
The very first lens I used this way was actually the very first "real" lens I ever owned - a ZeissJena 50mm that came with an Exa that I bought in 1972. It does not have this aperture stop-down tab.
This new purchase is an impulse, and I'm anxious to get my hands on it.