RE: [Leica] star pattern in lights when stopped down...

["Austin Franklin" <austin@darkroom.com>]

Why do you get double the number of points when you have an odd number of
blades?

> -----Original Message-----
> From: owner-leica-users@mejac.palo-alto.ca.us
> [mailto:owner-leica-users@mejac.palo-alto.ca.us]On Behalf Of Vozeh,
> Colin
> Sent: Thursday, February 01, 2001 11:19 AM
> To: 'leica-users@mejac.palo-alto.ca.us'
> Subject: RE: [Leica] star pattern in lights when stopped down...
>
>
> 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.
>
> C.
>
>
>  -----Original Message-----
> From: 	Austin Franklin [mailto:austin@darkroom.com]
> Sent:	Thursday, February 01, 2001 9:36 AM
> To:	leica-users@mejac.palo-alto.ca.us
> 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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