A look into the
development process
Leica is enhancing the
SL-System with a range of new Summicron-SL lenses. The first lens of this
series is the APO-Summicron-SL 75 f/2 ASPH. In this interview, five members of
the Leica team involved in the development of these lenses explain how it was
all made possible: Product Manager Steffen Skopp, Optical Designer Dietmar
Stuible, Heiko Schnaubelt from Electronics Development, Systems Engineer
Torsten Grabau from Construction, and Industrial Engineer Simon Jennemann.
The idea behind the new
Summicron-SL lenses is the combination of very high optical performance with
compact dimensions. What are the concrete advantages of this for photographers?
Skopp: With the
Summicron-SL lenses, we are giving photographers a range of first-class lenses
with exceptional performance. Their performance profiles are convincing in
every respect. The engineers have delivered unbelievable results, and have,
without a doubt, achieved new levels of excellence, not only in terms of
optical performance. The weight, balance, and handling are ideally harmonized,
and the haptic sensation and finish are in the absolute high-end category in
all respects. On top of this, we have their amazingly compact size and an
extremely fast and precise autofocus that lends the lenses lightness,
discretion, and such impressive precision.
The APO-Summicron-SL 75
f/2 ASPH. is the first lens of this series. Why did you choose this focal
length in particular?
Skopp: This focal length
has a long tradition at Leica. The perspective for portraits – that’s what the
choice of this focal length is all about – is significantly different from that
delivered by a 50 mm or 90 mm lens. You have to try out a 75 mm lens for
yourself to understand what this means in practice.
When did the development
process begin?
Stuible: We began working
on the Summicron-SL lenses quite some time ago, as a development in parallel to
the SL-Camera. It was clear from the start that we would need an entirely new
holistic approach to enable us to realize such high-resolution lenses with
state-of-the-art autofocus. This simply couldn’t be done with existing
technologies.
We set up an
interdisciplinary team that united expertise from the fields of optical
engineering, mechanical engineering, electronics, and production, and were
given the freedom to break new ground with innovations in all these
disciplines. The outcome of this was an entirely new optical and mechanical
construction concept, a cutting-edge AF system with Dual Syncro DriveTM and,
not least of all, a state-of-the-art, smart assembly line.
So what are the concrete
innovations in this new lens type?
Grabau: The key
technologie is the Dual Syncro DriveTM, which enables what we describe as
double focusing in our in-house terminology. Here, two separate lens elements,
each weighing only 10 grams, are moved for setting the focusing distance. We
developed an independent focusing unit for each of the two lenses. Because
these lenses are so light, we were able to utilize an extremely precise and
fast drive system based on stepping motors with which we can not only shift the
lenses to each focusing position with extreme precision, but can also travel
through the entire focusing range in a fraction of a second.
Schnaubelt: Our task in
Electronics Development was to ensure that the movement of the two independent
focusing units in relation to each other would be perfectly synchronized,
despite the high speed. Because, the camera takes pictures to analyze image
contrast while simultaneously giving the lens instructions on whether to carry
on focusing or whether maximum sharpness has already been achieved. At the same
time, the photographer may not experience a perceptible delay.
The key to the solution of
this problem is a complex control loop. This guarantees not only synchronicity
and speed, but also ensures the smooth movement of the focusing elements with a
minimum of vibration. In turn, this also enables us to reduce noise emission
levels to a minimum.
What is new about the
optical design?
Stuible: In many lenses,
focusing is by means of a conventional focusing mechanism that moves the entire
optical system, or by means of simple internal focusing, in which only one lens
group is moved.
In contrast, the low
weight of the focusing unit in the case of double internal focusing enables not
only fast autofocusing, but additionally delivers very good optical performance
in the close focusing range.
In this, we have an ideal
solution that fulfills all our demands, but differs significantly from all
previously known concepts. Lens elements and their refractive indices had to be
arranged in new configurations, new glass types had to be used and the optical
system had to include asphericals to create enough room for the two focusing
lenses and maintain high optical performance from infinity to the closest
focusing distance.
The 75 mm and the recently
announced Summicron-SL 90 are both APO lenses. Just how complex is the overall
optical design?
Stuible: Leica has always
stood for unrivaled imaging performance, and now, with the Summicron-SL, we
have once again set entirely new standards in the field of optical design. The
dynamic range and detail resolution in images captured with this lens are
extremely high.
The APO-Summicron-SL 75
f/2 ASPH. has a total of eleven elements, one of which is an aspherical. In
addition to this, all elements in the optical system are made from high-quality
special glasses. The aspherical corrects monochromatic aberrations and the
special glass types take care of chromatic aberrations. As a result of this,
even highlights remain completely free of color fringing. This then means that
the lens earns the quality seal ‘APO’, which is a Leica quality indicator.
I would like to emphasize
that the lenses are especially convincing in their performance at close
focusing distances. The combination of high detail resolution and a maximum
reproduction ratio of 1:5 delivers truly impressive pictures. Photographers can
rely on this exceptional imaging performance at all apertures and distance
settings.
Jennemann: The performance
of the optical design and mechanical construction is one side of the coin. The
other is the precision in manufacturing and production that ultimately delivers
the desired quality of the lens.
In the lens grinding
process, deviations from the specified surface geometry must be within
tolerances measured in wavelengths of light – in other words, significantly
less than a micrometer. The permitted tolerances for the centering of the
lenses are also measured in micrometers. For a clearer comparison: the
thickness of a human hair is approximately 70 micrometers. The guide rails upon
which the focusing units slide must also be precisely aligned to the optical
axis.
What influences does the
Dual Sycro DriveTM have on the mechanical realization and serial production of
the lenses?
Grabau: A Summicron-SL
demands the ultimate from manufacturing processes. The main element, the body
in which the motors and guide rails are mounted, is an extremely complex
construction. In addition to this, we have the enormous levels of precision
required, the quality of the components, and, of course, as the lenses must be
both robust and light, the choice of the materials we use. For instance, the
mounting components for the two focusing elements are manufactured from a
lightweight magnesium alloy that enables us to fabricate components with
extremely thin walls that simultaneously offer extremely high rigidity. We
always make use of the best materials available to us to ensure everyday
usability and endurance that express and fulfill Leica’s promise of quality
made in Germany.
Jennemann: One of the
greatest challenges is the ability to maintain consistency during serial
production. For this purpose, we have integrated a completely new assembly line
at the Leica factory in Wetzlar that unites the latest precision adjustment
technologies, software-supported process control, and the long-established,
traditional methods of lens manufacturing. For example, we mark many components
with 2-dimensional barcodes that tell us not only which components have been installed
in which lens, but also provide us with data for numerous measurements and
checks. These data are then utilized for monitoring and assuring the quality of
the manufacturing process.
The newly developed
devices for measuring and adjustments allow us align much more delicate
components than ever before with even greater precision – for example, we can
perfectly align two lenses in relation to each other in free space. This means
that we are now in a position to manufacture lenses that were previously
considered impossible to build.
Manual processes remain an
essential part of our manufacturing procedures: in construction, assembly, and
in quality assurance. Workplaces are precisely configured to meet the needs of
the members of the assembly team and the respective phases of the assembly
process. Optimum lighting, lean procedures, and partially automated parts
provisioning all play a role in ensuring optimum efficiency.
The performance data of the APO-Summicron-SL 75 f/2 are certainly very impressive, but didn’t your customers expect a faster lens?
Skopp: An important, but
until now missing, component of the SL-System is a range of compact
high-performance lenses. Fast lenses like a Summilux, for example, would have
to be considerably larger and heavier.
On the other hand, the
look of the new Summicron-SL lenses simply can’t be compared with anything
anyone has ever seen before. It’s hard to describe in words, you have to see
with your own eyes.
Stuible: The depth of
focus is actually significantly shallower than you would expect from the
f-number of the lens. Generally, you would expect two lenses of the same focal
length to have an identical depth of focus at the same aperture setting. In the
case of the Summicron-SL lenses, the resolution of details in the sharply
focused plane is extremely high and the difference between sharp and unsharp
areas of an image is perceived much more strongly than usual. Sharply focused
objects stand out more prominently, the overall impression is more
three-dimensional, and the impression of depth is enhanced – just as if the
lens were faster. This, in turn, opens up new opportunities for composition and
creative expression.
What are the key
characteristics of the design of the announced Summicron-SL lenses?
Skopp: The design concept
is consistent for all lenses, despite their different focal lengths. No matter
which of the lenses the photographer uses, the handling remains identical. The
balance is the same, the focusing ring is in the familiar location, the filter
thread has the same diameter, and the optical performance is also consistent.
This is an important aspect we learned from the lenses we make for
cinematography, the Summilux-C and Summicron-C lines. In terms of performance,
our orientation reflects the qualities of the Leica S lenses.
Grabau: All the lenses of
the series are very compact and light. At the same time, we paid particular
attention to robustness and long service life. As is already familiar from the
SL-System, seals around the front lens, in the focusing ring and on the bayonet
mount ensure that moisture and dust cannot get inside the lenses. In practice,
properties such as these are at least as important as outstanding imaging
performance.
Would you say that the
APO-Summicron-SL 75 f/2 ASPH. sets new standards?
Skopp: Yes. We have
managed to push the limits of the technically possible just a little bit
further. The innovations we require for this are becoming noticeably more
complex and more difficult, and what our team has delivered in the fulfillment
of our objectives is a truly formidable achievement. The 75 mm rings in a whole
new era, and we look forward to seeing what skilled and talented users will
create with it. Our ultimate goal is the creation of perfect tools for
photographers, and if this requires to push the limits, that is what we do.
To know more about the
Leica SL-System , please visit the official website.
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