Archived posting to the Leica Users Group, 1997/06/24

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Subject: Lens Diffraction
From: Richard Clompus <rclompus@voicenet.com>
Date: Tue, 24 Jun 1997 22:37:09 -0400

aglang@sprynet.com asked about using f 22 on the 28mm Elmarit lens for
prefocusing with the hyperfocal distance:
 
>but wouldnt it be better to use a wider f stop? Diffraction!

I agree that diffraction becomes more of an issue with aberrations for some
lenses beyond f 16.  I guess Leica in their optical wisdom felt the 28mm
Elmarit's optical design could hold up to f 22 without a major loss of
resolution or contrast.

Another interesting observation I have made with the 28mm Elmarit is that
the diaphram blades do not open all the way even though the lens is set for
f 2.8.  Its almost as if Leica could have perhaps made this lens an f 2.0
but felt the aberrations wide open wouldn't meet their strict criteria for
sharpness or contrast levels.

I am very pleased with the 28mm Elmarit.  For those of you who waer
glasses, the external finder is very handy.  I use it like a point and
shoot camera.  Very fast, very discreet.

Happy shooting,

Richard
- --------------------------
Richard Clompus, OD
West Chester, Pennsylvania, USA