Archived posting to the Leica Users Group, 1998/05/20

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Subject: [Leica] Q: lens diaphragm not circular when fully opened ?
From: (phong)
Date: Wed, 20 May 1998 18:21:04 +0000

   I just bought a 90mm Elmarit-M in mint condition from a fellow LUGer, 
   and noticed that the lens diaphragm does not open to a full circle
   when the aperture ring is set at the 2.8 (full aperture) detent.  It 
   looks more like a jagged circle with the end of the 9 (?) blades 
   protruding into the circle.  What is even more strange is that I would 
   open the diaphragm a bit pass the 2.8 detent, and the diaphragm becomes
   more fully circular, though still not perfectly so.

   None of my lenses (Leica and others) exhibit this phenomenon.  When
   set at full aperture, they are all fully circular.

   Has anybody seen anything similar ? Does anyone have a plausible
explanation ?
   Could this mean a sign of defect ?  Any suggestion to how to test the lens ?
   Perhaps shooting wide open into a backlit scene with some flare ?

- - Phong

P.S. The observation is made by looking through the unmounted lens from the