[Leica] Nokton report 1

[Erwin Puts <imxputs@knoware.nl>]

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The Nokton 1.5/50mm.

If you look at the development and evolution of high speed 50mm 
lenses, you will note  that lenses with an aperture of 1:1.4 leaped 
forward optically in the mid-sixties and then reached a plateau. 
Almost every 1.4 design is based on the Double Gauss formula and 
generally has 7 lens elements. One of the last 'new' 1.4 lenses was 
the Planar 1.4 for the Zeiss Contax in the seventies and its 
performance was not breathtaking to put it mildly. It is very 
difficult to design a 1.4 lens with a performance equal to the best 
2/50mm lenses.  Oblique rays in the tangential plane play havock with 
all good intentions of the designer. Do not forget that a 1.4 design 
admits twice the amount of light energy and aberrations grow 
disproportionally. Many of the specific 1.4 aberrations errors do not 
improve when stopping down, making a 1.4 more of a compromise than a 
2/50, which is a much more evolved type of lens design. So for 
decades designers had no serious option to improve on a 1.4 design 
(not possible or to expensive). Recently Leica introduced a 
redesigned Summilux-R 1:1.4/50 which is a big step forward to produce 
f/2 quality a 1,4 design. At 1,4 the Summilux-R offers a high 
contrast image with outstanding imagery on axis and a very good 
quality in the outer zones. The design utilizes the classical Double 
Gauss formula stretched to 8 lens elements.
The Voigtlander Nokton 1.5/50 is the most recent addition to the 1,4 club.
its design is closely modelled to a 'normal' 2/50 design with 6 
elements, but with the last element  a double aspherical one, that is 
both surfaces are aspherical. It is a rule that one aspherical 
surface replaces a full lens element in a full spherical design, so 
this lens can be compared to the 8 elements of the Summilux-R.
The use of an aspherical surface is not restricted to the correction 
of spherical aberration, as it is sometimes stated. Many more optical 
issues can be addressed with an asphere. In fact the Nokton has more 
residual spherical aberration than could be expected.
My version had some decentring which became visible in testing of 
course (one outer side of the image gave reduced contrast and a drop 
in performance. It could also be seen in real life pictures when 
large billboards were photographed. One side visibly gave a lower 
definition and loss of detail rendition. Not that much but still.
On test the full aperture gives a medium contrast overall image with 
a trace of veiling glare. On axis very fine detail was rendered with 
very good edge definition. This definition extended to the outer 
zones with only a slight loss of contrast and edge definition. This 
lens excells at a very fine even coverage over the bigger part of the 
picture area (neglecting the decentring for a moment, which might be 
atypical). Astigmatism is well but not fully controlled and lateral 
chromatic aberrations are very well reduced. You will see these 
effects in the outer zones as a reduced rendition of very fine and 
extremely fine detail and a high noise ratio which makes it difficult 
to detect separate details in the finer structures.  There is visible 
vignetting in the corners.

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<fontfamily><param>Times</param>The Nokton 1.5/50mm.


If you look at the development and evolution of high speed 50mm lenses,
you will note  that lenses with an aperture of 1:1.4 leaped forward
optically in the mid-sixties and then reached a plateau. Almost every
1.4 design is based on the Double Gauss formula and generally has 7
lens elements. One of the last 'new' 1.4 lenses was the Planar 1.4 for
the Zeiss Contax in the seventies and its performance was not
breathtaking to put it mildly. It is very difficult to design a 1.4
lens with a performance equal to the best 2/50mm lenses.  Oblique rays
in the tangential plane play havock with all good intentions of the
designer. Do not forget that a 1.4 design admits twice the amount of
light energy and aberrations grow disproportionally. Many of the
specific 1.4 aberrations errors do not improve when stopping down,
making a 1.4 more of a compromise than a 2/50, which is a much more
evolved type of lens design. So for decades designers had no serious
option to improve on a 1.4 design (not possible or to expensive).
Recently Leica introduced a redesigned Summilux-R 1:1.4/50 which is a
big step forward to produce f/2 quality a 1,4 design. At 1,4 the
Summilux-R offers a high contrast image with outstanding imagery on
axis and a very good quality in the outer zones. The design utilizes
the classical Double Gauss formula stretched to 8 lens elements. 

The Voigtlander Nokton 1.5/50 is the most recent addition to the 1,4
club. 

its design is closely modelled to a 'normal' 2/50 design with 6
elements, but with the last element  a double aspherical one, that is
both surfaces are aspherical. It is a rule that one aspherical surface
replaces a full lens element in a full spherical design, so this lens
can be compared to the 8 elements of the Summilux-R. 

The use of an aspherical surface is not restricted to the correction of
spherical aberration, as it is sometimes stated. Many more optical
issues can be addressed with an asphere. In fact the Nokton has more
residual spherical aberration than could be expected. 

My version had some decentring which became visible in testing of
course (one outer side of the image gave reduced contrast and a drop in
performance. It could also be seen in real life pictures when  large
billboards were photographed. One side visibly gave a lower definition
and loss of detail rendition. Not that much but still. 

On test the full aperture gives a medium contrast overall image with a
trace of veiling glare. On axis very fine detail was rendered with very
good edge definition. This definition extended to the outer zones with
only a slight loss of contrast and edge definition. This lens excells
at a very fine even coverage over the bigger part of the picture area
(neglecting the decentring for a moment, which might be atypical).
Astigmatism is well but not fully controlled and lateral chromatic
aberrations are very well reduced. You will see these effects in the
outer zones as a reduced rendition of very fine and extremely fine
detail and a high noise ratio which makes it difficult to detect
separate details in the finer structures.  There is visible vignetting
in the corners.
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