[Leica] 15mm: Leica vs Zeiss versions

["Anderson, Ferrel" <AndersonF@ria.army.mil>]

In answer to Eric Welch's question about the relative performance of the
Leica and Zeiss 15mm lenses.

Superwides were tested years ago by Popular Photography.  Performance was
presented in the form of MTF graphs.  Besides the subject lenses, the Pentax
15mm lens and one other brand (Nikon?) were tested.   The Zeiss and Leica
lenses topped the others easily, but the Zeiss bested the Leica lens.   Both
demonstrated equal qualities in the center and at the edges, but the Leica
version dropped below the Zeiss lens in the 2/3 out zone.   How could that
happen when it is well known that the two lenses are optically the same,
with the optical elements probably manufactured by Zeiss, and, I presume,
the manufacture of the mechanical components and assembly performed in the
respective companies' factories.  Sample variation is probably the best
explanation.  

Another explanation is the specifications for performance of the respective
companies.  The Leica lens was sold by Leica, and it is assumed that the
quality control department accepted it for sale.  This brings up a question
I have pondered for a long time.  Why don't camera manufacturers publish
their specifications for acceptable quality?  Avery other provider of  high
end equipment, especially in the commercial market, is essentially forced to
provide this information to provide a guarantee.