Re: [Leica] Lens evaluations

[Erwin Puts <imxputs@knoware.nl>]

>Laney's book "Leica Lens Practice" claims that Leitz (and later Leica)
>prefer "Edge Spread Function" over MTF measurements. The former is supposed
>to be a more accurate way of quantifying the characteristics of a lens
>associated with the "Leica look." (I even read some of the technical papers
>by Leitz staff cited in Laney's first edition and their rationale seems
>sound.) I now see that Leica is publishing MTF graphs of new lenses (e.g.
>in the PDF files available on the Leica web site). Does anyone know if this
>marks a change in Leica philosphy or are simply yielding to the fact that
>more people recognize MTF graphs and know what to do with them?
>

Never believe it, because it has been written in a book. The whole idea of
the Edge Spread Function and its use had the lifespan of a fly and lacks
any theoretical foundation. Mr. Laney was a bit too eager to introduce it
and the fact that he kept it alive in the second version does not bode well
for his optical knowledge. The head of the optical department who
introduced the concept, Mr Thomas, is one of the least memorable of all
Leica designers.
The publication of MTF graphs in no way marks a change in design
philosophy. They use MTF graphs quite a long time, long before the
'introduction' of the ESF. The proposition that more people now know how to
interpret an MTF graph, sounds quite optimistic. I for one am struggling to
find a meaningful interpretation for many aspects of these graphs. How to
interpret the fact that a given lens has a contrast factor of 35 at 40lp/mm
in the sagital direction on the 9mm distance. What happens if two lenses
have the same type of curve but the sagital and tangential lines are
exchanged.
These questions can be answered, but it takes time to do so.
Erwin