Tuesday, July 13, 2021

LEICA AND OTHER LENSES - A CLOSER LOOK


Leica 50mm f/2 APO Summicron M ASPH


By Heinz Richter

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.  It is also the case that the performance increases of Leica lenses due to their production methods are not equivalent to the increases in cost. These are disproportionally higher.  The market offers a number of lenses from other manufacturers which are relatively close in performance to their Leica equivalents.  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 more on this go here and here



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