Leica 50mm f/2 APO Summicron M ASPH
One of the most often
heard criticisms of Leica is that their equipment is too expensive. It is indeed the case that their price
structure makes it impossible for many to even remotely consider a Leica, leave
alone a Leica and a compliment of lenses.
But is it actually the
case that Leica equipment is simply overpriced, that it could be sold for
less? The answer is “NO.” Of course it would be possible to make Leica
cameras and lenses in a way to be sold for less, but that would be totally counter
to their long standing philosophy, to make their equipment to perform as well
as possible.
That philosophy started
with the original Leica from 1925. The
camera entered the market at a time when most camera equipment, especially
professional cameras and lenses were rather large, to produce large negatives
to ensure professional quality results.
From the very beginning, the
Leica was designed and made to assure results that did not have to fear
comparison to the even the best camera equipment available at the time. Much of this was due to the excellent lens
that Max Berek designed for the camera.
Leica Model A with the famous 50mm f/3.5 Elmar, designed by Max Berek
That design philosophy has
been maintained over the years and Leica still makes what have to be considered
the best lenses money can buy for any camera.
Unfortunately it is the
case that no manufacturer can make a perfect lens. Small deviations from a flawless
lens will always be present. Those deviations
will always influence the overall performance of a lens.
Subsequently, in order to
make a lens perform as well as possible, it is necessary to keep those
deviations from the ideal as small as possible.
Besides the basic design of a lens, to assure a high performance level,
it is necessary to apply the tightest tolerances possible. It is in this regard where Leica sets
themselves apart from the competition.
Virtually all other lens
manufacturers mass produce their equipment.
As good a mass production has become, it cannot reach the tight
tolerance level that Leica’s bench made process is able to assure. Instead of taking test samples every once in
a while, each individual manufacturing step is accompanied with a test. If the test reveals a flaw beyond the
acceptable parameters set by Leica, it is either corrected and retested until
the tolerances are within the set levels, or the item is discarded. This is the case with mechanical as well as
with the optical parts of a lens.
All production and assembly steps are done at individual work stations
Adjustments for the focusing mount being performed
Both the mechanical and
especially the optical tolerances far exceed those of other manufacturers. Mechanical tolerances of Leica cameras and
lenses have to be within 1/100 mm (1/2500 inch) while other companies’ accept
tolerance of 1/50 mm or even less. The
optical tolerances are far tighter. For
instance, Leica applies a standard of ±0.0002% for the accuracy of the
refractive index. This compares to the
international standard of ±0.001% as applied by other lens manufacturers. The accuracy of the Abbe number, the measure
for dispersion, is ±0.2% for Leica compared to ±0.8% internationally.
All lens elements are ground individually with precision grinding machines
Once the raw glass blanks
have been received and tested for the proper accuracy of their properties, they
are ground to their specified shapes.
For the manufacture of individual lens elements Leica allows production
tolerance of no more than ¼ lambda or ¼ of the average wavelength of light
which corresponds to approximately 500 nanometer or 0.0005mm for the accuracy
of the lens surface. In comparison, the
tolerances applied by other lens manufacturers are ½ lambda or 0.001mm. Similar tolerances are used for the thickness
of the elements and proper centering along the optical axis.
As of late many
manufacturers are offering lenses with aspherical surfaces which can greatly
improve lens performance by virtually eliminating spherical aberration. However, there are two distinctively
different approaches in the manufacture of these elements. An inexpensive method is to produce a
“conventional” spherical element and sandwich it with a thin aspherical surface
element. These are made of precision
molded acrylic. However, this method,
originally developed by Zeiss, was ultimately discarded by them because it
could not approach their quality standards.
The main cause was the fact that even the clearest plastics, like
acrylics, consist of very large molecules.
Light, when transmitting, literally will scatter off these molecules,
causing the light to be slightly diffused, which ultimately has adverse effects
on lens performance. Other companies use
precision molding equipment where a glass blank is reheated until it becomes
pliable and then is precision molded into the final shape of the lens
element. Some exotic types of glasses
cannot be used with this method because the reheating and molding will cause
the glass to deteriorate and thus make it useless. Subsequently, this precision
molding process forces the lens designer to compromise to a certain degree
because better suited glasses cannot be utilized. The same applies to lens elements of larger
diameters. Leica uses an entirely
different approach. They use computer
controlled automatic grinding and polishing of the glass elements which require
the adherence to extremely tight tolerances.
Unfortunately such production methods can only be achieved at
considerable expense.
Precision grinding of aspherical lens elements
The grinding compound for many lens elements must be continuously agitated to avoid deterioration
For the production of
aspherical lens elements Leica applies tolerances which cannot exceed 0.03
micrometer or 0.00003mm. To achieve such
precision Leica employs special grinding machines where the lens element is
rotating against the grinding head, which is in form of a narrow rod. This will grind only a small section of the
entire surface of the lens element at a time.
A special grinding substance is also used which is partially
magnetized. This is done to allow for a
more precise adherence of the grinding substance to the lens and grinding rod
surface. With all lens elements the
grinding substance becomes ever finer from one step to the next until it is
mostly water with a small amount of a very fine polishing compound.
Grinding aspherical
surfaces via the method used at Leica is extremely time consuming. As with all manufacturing steps at Leica,
each individual step is immediately followed by a check. If these checks show that deviations from the
norm still exist, the step is either followed by additional work, or the lens element
is discarded. This often leads to no
more than five aspherical lens elements being produced in a single day.
Each manufacturing and assembly step is immediately followed by a check
To increase lens
production, Leica tried to outsource the manufacture of some aspherical lens
elements to other companies.
Unfortunately this proved to be a dead end. The companies that were approached by Leica
either were not able to work within the specified tolerances or they simply
were not able to supply a sufficient number of elements to make such
cooperation feasible.
All of this makes Leica by
far the foremost and most advanced manufacturer of aspherical lens elements in
the world.
But there are other
differences that some manufacturers apply to save cost. Some time ago I came across a rather
astonishing example. Someone gave me a
lens to see if I could repair it. It
would not focus to infinity. I agreed to
give it a try.
This was a 90mm macro lens
from a well-known aftermarket lens manufacturer. A simple look under the outside focusing ring
revealed that these lenses were all made without any attention to the actual
lens to film/sensor plane of the camera.
The different lens mounts were all installed the same. For a fine adjustment these lenses had a very
short, additional focusing adjustment in the back, to adjust for the different
make of camera they were to be used with.
This is a relatively simple adjustment, and once done, all that is
necessary to secure the final position.
Any reasonable person
would expect that this adjustment would be secured with a few screws. However, no such screws were present. Instead
the adjustment was “locked” in position with a piece of tape. A heavy duty tape, not unlike Scotch tape was
applied. It was this tape that had
slipped a bit, preventing the lens from focusing to infinity.
A while later a similar
situation occurred, this time with a rather expensive zoom lens for video
cameras. Video lenses routinely have an
infinity adjustment to be able to be used on a variety of cameras.
Remembering my experience
with the 90mm macro lens, I thought if the same happened with this almost
$3,000 lens. Shure enough, the same type
of tape was used to secure the infinity setting and once again the tape had
slipped.
I am not saying that all
lenses outside of Leica use such severe shortcuts to arrive at a lower cost,
but it clearly shows that a lot of money can be saved along the many manufacturing
steps of a lens.
I have had the opportunity
to tour the Leica factory in Wetzlar on several occasions, not only the common
visitor tour, but I have been allowed on the actual manufacturing floor. The precision and effort that goes into each
piece of equipment is astonishing. Even
the testing equipment is amazing. Leica
buys their testing equipment from specialty manufacturers, but in many cases
they will improve its capabilities by modifying it to meet their standards.
All of this unfortunately
is expensive and it obviously is reflected in the cost of Leica equipment. If the additional cost is worth the gain in
performance is a question that everyone has to answer for him/herself. I for one am very glad that I have this
choice.
For other articles on this blog please click on Blog Archive in the column to the right
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