Introduction

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Leica R-Lenses
by Erwin Puts

July 2003
Introduction

Leica R-Lenses

Introduction
__The R-System
The first lenses for the Leicaflex have been introduced in 1965
in the then classical focal lengths of 35,50, 90 and 135mm. The
Summicron 50mm had a maximum aperture of 1:2, all the
others were Elmarit-versions with an aperture of 1:2.8. The
quality of the mount was immediately recognized as the best in
the world. These characteristics: sufficiently wide apertures
and all metal mounts with excellent ergonomics are still true
today for all lenses within the R-system. I could myself convince of the longevity and sustained accuracy over many years
when I was able to test and check several scores of older lenses, often very heavy used. Every lens, even the most worn out
ones, were within the originally specified tolerances and there
was not a sign of decentring, one of the earliest signs of degraded performance. The optical performance was as expected
from a new lens just out of the box.
The R-system has been developed and evolved over the years
from 4 lenses with focal lengths from 35mm to 135mm to 26
lenses with focal lengths from 15mm to 800mm. The average
age of all lenses is 11.5 years. Six lenses are less than 5 years
old, eleven lenses are less than 10 years old and nine lenses
have an average age of about 20 years. This last group of lenses has focal lengths from 24 to 100mm and the optical layout
is mostly a Double-Gauss variant. This lens type is based on a
very mature design and it is not easy to improve on the performance within acceptable financial and ergonomic constraints.
The Summicron-R 1:2/50mm as example is still the best standard lens for reflex cameras. This range of lenses between 24
and 100mm has been complemented in the last decade with a
series of high performance zoomlenses.
If we look carefully at the introductions in the last decade we
can see where the development efforts will be focused on and
what a possible road map could be. Actual and future mainstay
of the range will be the zoomlenses and those fixed focal
lengths that are eminently suited to manual focusing, like the
very wide angle lenses (15mm to 19mm), telelenses with
superb performance that can be used handheld (!80mm to
300mm) and specialized lenses with very wide apertures like
the Summicron-R 1:2/180mm. The image quality of the R-lenses should enable the photographer to exploit to the full extent

the potential of the imaging chain and to implement creative
imagery with great clarity of vision.

__The construction
Several limitations are imposed on the design and construction
of R-lenses. The most important are the back focal length, that
is the distance from bayonet flange to the front of the film
plane (in this case also free space for the mirror movement),
the manual focusing mechanism and the the mechanical aperture control. You can not create an arbitrary small lens because
you need space for the mechanical functions and the mounts.
And the aperture and focal length have some influence too. A
180mm lens with a maximum aperture of 1:2 will have a front
lens diameter of at least 90mm. Size and weight are important
limiting parameters when designing a lens. If you are able to
create small lenses, as with the Minox camera, you will encounter less problems with the correction of optical aberrations.
That is one of the reasons why the Minox lenses are so good. If
you can design a lens without any consideration to weight and
size, you can compute a system with many lenses and so reach
a very high level of quality. In practical terms, one will have to
find a smart middle course and one has to balance the conflicting demands to reach a delicate and individual equilibrium.
Every optical designer will set his/her own emphasis and will
accentuate certain characteristics.
When designing long focus lenses and high speed retrofocus
designs, the back focal length and the bayonet diameter will
influence the location of the exit pupil, and this must be chosen
carefully. It is really not a simple matter to create a design that
will satisfy all demands without some reduction.

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Leica R-Lenses

Introduction
__Retrofocus lenses

__Telelenses

A retrofocus lens is characterized by a back focal length that is
longer than the true focal length. The Leica R mirror box asks
for some space and the back focal length is 47mm. A lens with
a focal length of 15mm will only fit if you can lock the mirror in
its upward position. This was indeed the only solution in the
past. The designer created so called symmetrical lenses, consisting of two identical groups of lenses, that were mirrored
around the aperture stop. A simple and brilliant solution: several optical aberrations generated by the fist group, could be
compensated fully by the second group. But the disadvantage
of the blocked viewfinder path was too great and so the retrofocus lens was developed. At the beginning the image quality of
the retrofocus design was less than what could be expected
from the symmetrical design. The first generation of retrofocus
designs were simply normal lenses wit a negative lens put in
front. In the course of time this type has been evolved to a new
type of design with very promising possibilities. Today one can
calculate retrofocus designs that are as good or even better
than symmetrical lenses (see illustration below). The necessary
effort is however much higher and the lenses will not be as
small. It is extremely difficult to design a compact retrofocus
lens without compromising the image quality. On the other
hand the location of the exit pupil can be used to reduce the
amount of vignetting.
Without floating elements a good performance in the near
focus range at wider apertures is quite a task. Leica will use the
method of floating elements whenever needed. But then the
opto-mechanical complexity increases and the Leica photographer may find him/her self lucky that the Leica company has this
almost fanatical aspiration to reduce the mechanical tolerances
to the level that production machinery nowadays can consistently deliver.

There are some aberrations that become a downright nuisance
when the focal length increases. A longer focal length implies a
higher magnification of the subject and also an enlargement of
chromatic aberrations.You need special glass types to correct
these errors. The use of new glass types from among others
Schott, Hoya and Ohara, the so called glass with anomalous
dispersion, is required to correct the optical errors to a high
degree. But these glasses are difficult to manipulate and also
very expensive. And it makes no sense to employ this glass if
you can not mount and check the manufacture with very narrow
tolerances. With the help of these glasses, you can design lenses with excellent performance (if you have understood the
optical system) and there are some superb lenses in the Leica
program that are a serious challenge for the capabilities of the
user. If you have understood the the performance profile of
such a lens, you can create astonishingly good pictures.
If you correct the chromatic aberrations to a particular high
degree, the lens is called an apochromatic design. Such designation is however not an objective criterion and so the transitions are fleeting. Where an apochromat starts and an achromat ends is not easy to define in practice. The Apo designs
from Leica have a vanishingly small amount of residual chromatic errors and can be called apochromats. There are some
photographic situations where the subjects will exhibit some
small color fringes at the edges, specifically when the dark subject is positioned against a very light background.
The second characteristic of modern telelenses is the use of
internal focusing. Here a lens group will be moved over a small
distance in order to improve the image quality over a wider
focusing range. In addition the focusing movement can be
much smoother as smaller masses will have to be moved over a
shorter distance.
The small movement must be controlled quite accurately, otherwise the result will be worse than without this method.

An example for a modern retrofocus wideangle lens (19mm f/2.8)

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Introduction
__Zoomlenses
Zoomlenses and Single Lens Reflex cameras form a natural and
harmonious unit. The focal length can be changed continuously
and you can see the changes in the viewfinder in order to select
the appropriate framing of the subject. The Leitz company has
for a long time expressed their hesitancy with respect to the
optical excellence of zoomlenses compared to the fixed focal
lengths. The first zoomlenses (Zoomar 36-82 or Nikkor 43-86)
were indeed not revolutionary, but they ofefred an additional
added value to practical picture taking that exceeded their limited performances. From the moment that one could improve
the quality substantially (with improved understanding of the
lens type, new optical design programs, effective coating of the
many lens elements) all major lens manufacturers have concentrated on this type of lens. Even leitz had a special department
for the analysis and design of zoomlenses, but limited to the
systems for the Leicina, a movie camera that was quite important in those days. The knowledge that was acquired was not
transferred to the photo department, even though the famous
Dr. Walther Mandler, head of the optical department at Leitz
Canada wrote in an article in 1980 hat according to his studies,
zoomlenses could deliver image quality as good as that as that
of the corresponding fixed focal lengths.
From 1992 (about ten tears later) new zoomlenses have been
designed by Leica. It new start had to be made as the previous
experience and knowledge was of limited value. It is the great
accomplishment of Lothar Kölsch, then head of the optical
department of Leica, to redefine the performance level of
zoomlenses to an all time height. The first original Leica zoom
is the Vario-APO-Elmarit-R 1:2.8/70-180mm.

__The idea of moving lens elements
A zoomlens is basically an optical system that has a changeable
magnification ratio while maintaining the focus position. A
zoomlens has two requirements: (1) the focal length must be
continuously variable and (2) the distance setting (focus position) must not change so that the object stays focused correct-

Leica R-Lenses

ly. Generally one can accomplish this with an optical system
with two moving lenses (or lens groups). If you look at the very
complicated lens diagrams of current zoomlenses, you may feel
surprised that the basic idea is so simple.
Let us start with the basics. Assume we have only two lens elements. One element is needed for the change of focal length
and the other one for the distance setting. It does not matter
which lens is used for what function. When you move one lens
over a small distance, the focal length will change or what is the
same the magnification ratio. Now you must move the second
lens over a certain distance to compensate the focus position.
Both lenses can be coupled mechanically so that a change by
one element automatically will move the other element over the
required distance. You could imagine the following construction: both lenses are mounted in one tube, that has two grooves
with a certain length and angle of inclination. Both elements
will move at the same time within these grooves. Now we can
start to understand the basic problem of zoomlenses. One of
the elements can be moved in a linear fashion, that is a straight
line. The other one must move in a nonlinear fashion. The optical explanation is quite daunting and will be skipped here. The
resulting shape of the nonlinear curve can be very elaborate
and is very laborious to construct with the required accuracy.
Even more difficult is a shape where the movement of the lens
has to be reversed and one must provide a twist in the curve.
As the movement of all elements has to be accomplished with
one turning movement of the lens mount, one needs a quite
complicated shape of the curve that is very expensive to manufacture. This method of lens coupling is called the mechanical
zoom compensation.
The second method of compensation is called the optical compensation. This one has the advantage that all movements are
linear. Biggest drawback is the fact that the focusing is only
accurately compensated for a few positions of focal length. At
all other positions the image is slightly unsharp. The user has to
adjust the focus manually. With autofocus systems there is no
problem as the AF sensor will detect this unsharpness and can
refocus. Systems with optical compensation are quite elaborate
as one needs more lens elements and groups (up to 5 moving
groups). Then we may expect problems with the accuracy of

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Leica R-Lenses

Introduction
mounting, the transparency and flare.
Leica has basically chosen to only employ the method of
mechanical compensation. This construction has definite
advantages. On which more later.

__From principle to construction
The basic design with two moving elements is just theory. The
optical designer wants to create a very good overall level of
error correction and to secure this performance over the whole
magnification range of the zoomlens. In this case the two elements are hopelessly inadequate. In addition one needs two
fixed lens groups, a front group for manual focusing and a
master group at the rear part. This master group is known from
normal photographic lenses and defines the angle of view and
the maximum aperture of the system. Between these two
groups you will find the linked moving elements. The overall
complexity is dependent on the required level of optical correction.
You can also change the fixed front group (for focusing) to a
moving element and it this case there are three moving groups
and has the front group a double task. Leica has zoomlenses
with different designs in the program. The first design by Leica
was the Vario-Apo-Elmarit-R 1:2.8/70-180mm and has 13 elements with a very high performance profile. The Apo-Elmarit-R
1:2.8/180mm has 7 elements and delivers an even higher performance. This comparison is not entirely honest, but it does
indicate the higher level of effort that is needed for complex
zoomlenses. On the other hand can you use these additional
elements to improve the quality if you understand the optical
system. There is a rule of thumb in optical design that says that
it is better to distribute the total power of the system evenly
over the lens elements. With more elements this is somewhat
simpler. In addition the designer will pay attention to the fact
that the contribution of every lens surface to the total optical
error of the system has to be minimized. This is only feasible if
you understand the shapes of the curvatures very well in their
error contribution. The creative mind is the most important
asset in lens design and superior to any computer program
when really good solutions are requited.

The optical designer has more degrees of freedom when
he/she has control over more elements that can be moved within limits and the possible error correction can be of a very
high order indeed. But to make a high quality zoomlens that will
deliver at all focal lengths within the zoom range the movement
of the sliding groups should be as small as possible. The twogroup design with mechanical coupling is the preferred solution
within the current range of Leica zooms. The Vario-Elmar-R
1:4/35-70 and the Vario-Elmar-R ASPH 1:3,5-4/21-35 have this
design. The Vario-Elmarit-R ASPH 2,8/35-70 has two moving
groups and in addition a "floating element" to add error correction. Here three groups are moving in concert.
These two-group moving systems are excellent solutions for
zoomlenses with a zoom range between 1:2 and 1:3. Examples
are : 21-35 makes 1:1.66, 35-70 makes 1:2.0, 70-180 makes
1:2.5.
With this system, one can get outstandingly good results, but
the manufacturing process has to work with narrow tolerances.

__Metal mounts
The meal mounts of Leica lenses make it possible to work within these tolerances, that are below 0.01mm in many cases.
The Leica mounts are produced nowadays with CNC machines
and every part will be carefully and painstakingly finished
manually by experienced workers. The mechanical control of
the movement of the lens groups functions within minute tolerances and that is indeed required. After having found the correct framing of the motive by changing the magnification of the
lens, you do not want to have to refocus, which is a nuisance
and will disturb the act of photography. When using AF
cameras, the requirements are less precise, as a small unsharpness will be corrected by the AF system. In a general
sense, one should know the limitations of the AF system. AF is
extremely fast, much faster than what one can accomplish
manually with eye-hand coordination. AF systems are not very
exact in their focusing. I have noticed this personally when
testing systems from several well known manufacturers.

The complex barrel construction of the Vario-Apo-Elmarit-R 70-180 mm f/2.8

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Introduction

Leica R-Lenses

Movements of the optical groups when changing the focal lenght (Vario-Elmarit-R 35-70 mm f/2.8 ASPH.)

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Leica R-Lenses

Introduction
In many instances I had to refocus after changing the focal
length to get a sharp image of the subject. And many photographers switch off the AF function when they need really accurate
focus. It is without any doubt that AF is a great help and often
necessary when you want to capture fast and unpredictably
moving subjects. But there are many motives where accurate
focusing is more important than fast focusing. Here one enters
the domain of Leica-R photography.
Metal mounts are an important characteristic of Leica lenses.
But one should keep a sensible eye on the matter. There are
opinions that claim that synthetic materials are inferior to metal
parts. This is not true. Synthetic materials has many characteristics that are quite valuable in precision engineering mechanics. A negative attitude is a thing of the past. But synthetic
materials are best suited in mass production situations, because the individual parts can be made by dedicated machinery
that are custom made and must be depreciated in a short period. Metal mounts are always slightly larger than comparable
synthetic components, but the size should be kept in reasonable dimensions. If one could built without restrictions, the
optical designer can create aberration free lenses. One can
then use as many lenses as needed and can create many
degrees of freedom, including lens diameters. This can be seen
in the field of micro-lithography where lenses are used for the
chip manufacture and were 30 lens elements for one system
are not an exception.

engineers, as there is force involved. And the transmission of
forces by mechanical means is not that simple. The time parallax between the moment the shutter is tripped and the closing
of the diaphragm should be small and work without resistances. The position of the diagram is not really free with telelenses as it cannot be placed to far in the front part of the lens.
Mechanical constraints, optical demands and ergonomic criteria together define the construction, shape, handling and
weight of a lens.

__Focusing
The focusing movement is accomplished with parallel threads
and the movement must be very precise, tight and smooth at
the same time. And backlash may not be detectable after decades of use. The choice and tooling of the materials is very critical. To enhance the smoothness of operation it now customary
to employ internal focusing groups. While smoothness is improved, the demands on accuracy increase. But leica often uses
constructions that are not mentioned in the literature. The ApoElmarit-R :2.8/180mm not only offers a superb performance
profile, but also a patented focusing construction and a new
form of the aperture blades. The customary discretion of the
Leica engineers not to disclose their accomplishments, has its
virtues, but many fascinating details are kept in the dark.

__Performance profile and lens personality

__Ergonomics and size
A lens needs a very good ergonomic shape, especially if it is
used manually. The size of a lens depends on a few parameters.
The most important are the focal length, and the front and rear
lens opening (the maximum aperture and the bayonet diameter). R-lenses are also constrained by the back focal length
(mirror box and space for moving mirror). Not only the focusing
is manual, but the diaphragm mechanism is mechanically actuated too. This fact is important as you need room for the
mechanical linkages. Actually this linkage is a challenge for the

Leica R-lenses are characterized by a very homogeneous performance profile: the optical quality is very high, but the performance peak is not an isolated value. You could design a lens
with excellent values at a certain distance and aperture, but
and lower values at all other positions. With Leica lenses one
can expect the same high quality at all apertures and object
distances, and for zoomlenses over all focal lengths. This optical performance is accompanied by a very good ergonomic
design. These goals can be attained because the metal mounts
allow for the accuracy and precision that is needed.

Mechanical precision down to the finest details

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Introduction
And we need this accuracy as there is no AF system that can
smooth out small errors in mechanical accuracy. Here the circle is closed: because there is no AF, a higher level of precision
is required and that can be delivered only when using metal
parts that are individually and manually finished. And the current requirements can only be met when the zoomranges are
not too extended.
Every lens for a photographic purpose is a compromise between many often conflicting demands. Size and weight and
correction of optical errors are interlinked parameters. The
word 'compromise' is probably not the right designation as it
could give the impression that we are talking about a less desirable solution. It would be better to talk about an equilibrium
condition. The optical designer searches for an optimum solution within the allowable space conditions and will balance
third order aberrations with fifth order aberrations. This balance will be different for a standardlens, a wide aperture wide
angle retrofocus lens or a zoomlens. You can not characterize
the profile of a lens along a unidimensional scale. A wide angle
lens has requirements that are different from a tlelens and
what is acceptable for a wide angle lens, may be anathema for
a telelens. In this area individual and personal views play some
role and the definition of the image quality is a bit personal.
Optical designers are very creative people who will select one
specific design out of many possible solutions, that they accept
as the best possible design, but there are no objective standards.
That is why every Leica lens has an individual personality within
a family likeness. A Summicron-R 1:2/50mm is a classical six
element Double-Gauss design, of which hundreds of variants
exist. There are bigger and finer differences between the many
design forms and the individual aberration correction. Precisely
these smaller differences do define the final image quality and
the fingerprint of the Leica lenses. One needs a bit of time and
discipline to discover these finer characteristics and use them
to good effect during picture making.
The lens reports that follow, will expand on these issues.

Leica R-Lenses

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