A bit confused about speed-less aperture of Mir-1b 37mm f2,8 year 1993

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Leclettico
Leclettico New Member • Posts: 11
A bit confused about speed-less aperture of Mir-1b 37mm f2,8 year 1993

Hi.

I received my first M42 mount lens: a Mir-1b 37mm f2,8 of 1993 (not so happy about the comas at 2,8, but I was warned).

I think that I'm not understanding the speed-less aperture.

The 1st ring, near the front lens, adjust the aperture with a red dot, from 2,8 to 16.

The 2nd ring, just below the 1st one, adjust the speed-less aperture with an another red dot.

But, If I set the 1st ring to 16, and the dot on the speed-less ring also on 16, the aperture is fully open, like a 2,8.

Viceversa, If I leave the 1st ring on 16 and move the 2nd ring dot to the 2,8 value, I have a full close aperture, like a 16. (In the Image below I stopped at a value of 4 to show you the red dot on the 2nd ring)

What?

I'm very confused.

I didn't find anything on internet. May you explain to me this aperture system?

Thx.

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