Archived posting to the Leica Users Group, 1998/04/11

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: Re: [Leica] Leica-Users List Digest V2 #305
From: TEAShea <TEAShea@aol.com>
Date: Sat, 11 Apr 1998 15:36:54 EDT

<<  "It remains Leitz policy not to design lenses purely to achieve
 high resolution of flat two-dimensional test charts, but deliberately to
leave
 intact a modest degree of aberration and curvature of field to improve the
 rendition of three dimensional subjects. 
 
 Does Leitz still follow this design policy, does anyone know? Or is optical
 bench sharpness the new standard.
  >>

It is certainly not true with the several newest Leica lenses.  I doubt if it
was ever true.  The new Leica lenses are able to provide high resolution, high
contrast and little curvature of field.  This is a difficult thing to
accomplish since there are usually trade offs.  However, the new Leica designs
have been very successful in accomplishing these goals.  

One of the issues that was mentioned is curature of field.  A few recent
examples --- The current 75 1.4 and 50 1.4 both have substantial curvature of
field.  The 35 1.4 non aspherical also had substantial curvature of field.
Because of the substantial curvature of field, these lenses "tested" very
poorly at the widest two stops on two dimensional parameters.  The effects of
depth of field at wider apertures tend to mask the curvature of field.  

In the newest lenses including the 21 2.8 aspherical, the 24 2.8 aspherical,
and the 35 2.0 aspherical, there is very little curvature of field.  The new
35 1.4 aspherical has some curvature of field but much less than the older
generation of lenses.

I do not doubt that some photograpers may like the soft and round look of the
older lenses with their greater aberations and curvature of field.  Sometimes
I like this look myself.  However, it would be curious to find a Leica lens
designer intentionally trying to design in curvature of field, if he could at
the same time keep the same level of resolution and contrast.  Some Leica
lenses did intentionally have substantial curvature of field because this was
a trade off to achieve higher levels of contrast or resolution.  At that time
they could not achieve everything in the same lens.

Tom Shea