Archived posting to the Leica Users Group, 1997/08/03

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Subject: Re: 50 DR Continued
From: Dennis Painter <>
Date: Sun, 03 Aug 1997 17:30:38 -0700

Stephen wrote:
> > > Don't the original rigid and DR Summicrons share the same optical
> > formulae?
> > >
> > > Dan C.
> >
> > Dan,
> >
> > Yes they do.  I believe that all the DR Summicrons tested out at the
> > exact focal length for which the Summicron was computed.
> Optical formula and focal length are entirely two different factors.
> Whether its a 7 element lens or a single element, they can have exactly
> the same focal length. Number of elements can be the same, focal length
> can be the same, and you can still have different optical formulas.
> Stephen


Sorry I was not clear on my statement.  I believe the original 50mm
Summicron and the DR Summicron share the same optical formula.  However,
due to tolerances, when a lens is manufactured it will not alwaya
measure at the exact focal length used in the computation of the

Assume for illustration that the focal length used in the optical
formula of the Summicron was 51.9mm.

Lenses are being manufactured according to this formula and two samples
are tested.  One measures 51.9mm another 51.2mm.  Are the equivalent?
are they both capable of the same performance?  I can't answer these
qustions.  My comment meant that I thought that all DR Summicrons
measured at the exact focal length used in the formula, (51.9mm in this
illustration), they were selected from production firstly on that basis
and perhaps other tests were then made.


- -- 
Experience is a tough teacher. It gives the test before the lesson.
- -unknown