[Leica] imag quality old and new (never ending story)

[Frank Dernie <FrankDernie@compuserve.com>]

Erwin wrote
>The number of elements and groups only indicate family resemblance.
>Extrapolating this fact to indicate similar designs is a bridge too far.
>Lens designs differ by curvatures of lens elements, distances between lens
>elements and glass types. Even if the overall resemblance is close, these
>paramaters really define the performance of a lens. And these differences
>are not disclosed by most published lens diagrams.

I am fascinated by lens design. OTOH I have never done any testing and do
not claim to be much of an expert.
OTOH I own many books on different lens designs. At least two of them have
element schematics of the older (pre Solms) Leitz lenses. There are family
resemblances between different lenses, the most common being the Elmar,
with 4 elements in 3 groups where the layout and element type are the same
but the actual curvatures and diameters vary with focal length and, I
suppose, aperture.
The second version 50mm Summilux M, 75mm Summilux M and 80mm Summilux R
have the same design. (the noctiluxes(?) 1.2 and 1.0 are both quite
different from these and each other). That is to say, each element is
equivalent in shape, position and whether cemented or not. Obviously the
silhouette type schematics are not dimensioned and the glass and coating
are not specified, but these are as closely related as, for example, the
35mm and 50mm 1930s Elmars. I won't bore you with a list of other families,
most people are not as fascinated by the engineering as I am.
Cheers Frank