by ʇolɐǝz ǝɥʇ qoq

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What is the little metal piece attached to the aperture ring in some Zeiss lenses?

What is its purpose?

It is like a little gun sight.

See for example the Planar T* 1.4 50 where the "gun sight" is below the 5,6 number. Planar T* 1.4 50

Thank you.

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up vote 7 down vote accepted

It was a physical coupling for early built-in exposure meters. It hooked into a coupling pin on the camera body to tell the exposure meter what f-number the lens was set at.

It looked something like this: Nikon F2 Photomic

Nikon F2 Photomic, 1971, from

Here's the user's guide, look for "Lens Aperture Coupling".

As for why Zeiss still has it on their lenses? I guess they don't want to leave owners of older cameras in the lurch :)

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For sure, the external aperture coupling ring from the Nikon F. (I think it actually predated the F). I have six or eight Nikkor leses from this era. Sadly, many newer Nikon bodies will not mount these lenses. The F-mount is the same, but the tang has interference with the pentaprism on newer bodies. – Pat Farrell Jan 1 '13 at 20:17

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