Any owners of the SOM Berthiot Paris Angulor 1:3.3 F=28mm L39?

[nitroplait]

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I got this sample expecting that it was defective as the aperture blades don't fully open when the lens is set to max aperture F/3.3.

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So, I looked around on the web for more information. No one mentioned this phenomenon but I found  this video on Youtube which seem to show the lens in the exact same state at f/3.3:

That confused me.

I put my lens on a digital camera set to 200 ISO, set the lens to f/3.3 and got a shutter speed reading of 1/30 when pointing to an evenly illuminated surface.
I got same result with a modern 28mm set to f/3.3 pointing to the same surface.

The logical conclusion is that my sample is working correctly. But I can't help thinking that almost half closed aperture is very weird. 

Any owners of this lens who can confirm it displays same behaviour?

 

 

Edited 1 hour ago by nitroplait

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[jerzy]

formula is A(perture)= f(ocal length)/D(iameter of opening). For your lens, when aperture set to 3,3 opening shall be roughly 8,5mm in diameter. There could be optical performance reasons why lens is throttled

[luigi bertolotti]

I have not that lens (no many owners, I think... a fine collectible, compliments !) but an iris that looks not fully open with lens wide open, is not rare in short focals with rather wide front elements... I'd bet that if you remove the diaphragm, you get a 28mm f 2 or 2,5/2,8 with strong vignetting and/or distortion at edges.

Edited 13 minutes ago by luigi bertolotti