Archived posting to the Leica Users Group, 2001/02/01

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Subject: RE: [Leica] star pattern in lights when stopped down...
From: "Vozeh, Colin" <>
Date: Thu, 1 Feb 2001 11:19:03 -0500

I'll take a guess and say diffraction - light bending around edges.  Each
straight edge produces another "spike" of light, so the star has as many
points as the iris has blades.  It's always more pronounced the more you
stop down.  It happens to all the light rays coming into the lens, but of
course the bright sources are what you notice.  I guess this is why the
greatest sharpness for all lenses typically doesn't occur at small
apertures.  For what it's worth, to my eye this is one instance where fewer
iris blades actually make a nicer image. 


 -----Original Message-----
From: 	Austin Franklin [] 
Sent:	Thursday, February 01, 2001 9:36 AM
Subject:	[Leica] star pattern in lights when stopped down...

What is the optical phenomenon that causes the star patter that is equal to
the number of aperture blades, seen when stopped down, in some lenses?

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