This is the Optical Design Department- Eleventh Edition [LEICA DG VARIO-ELMARIT 12-60mm/F2.8-4.0 ASPH./POWER OIS]
Hello everyone.
"This is the Optical Design Department" is a series that takes an in-depth look at LUMIX lenses.
In "This is the Optical Design Department", we will explain the lens designs and their features, as well as the dedication and philosophy behind our work that you will not find in our catalogues or websites.
For those who are considering purchasing a LUMIX lens, we encourage you to learn about the design philosophy behind LUMIX lenses, and for those who already own a LUMIX lens, we invite you to discover the passion that has gone into creating its superb image quality.
This is an article that explains various lenses written by developers full of technical jargon.
By reading this, you too will be peering into the depths of lens buying addiction.
The 11th article is about LEICA DG VARIO-ELMARIT 12–60 mm F2.8–4.0 ASPH. POWER O.I.S, explained by Kurioka-san.
Discussion of New Lenses
The LUMIX line-up of standard lenses for the Micro Four Thirds system includes a wide range of models with diverse specifications, from motorised zooms and retractable zooms to fixed-aperture lenses and high-magnification zooms.
This reflects the fact that standard-range lenses are versatile tools, suited to a wide variety of situations, and that our customers enjoy using them in many different ways.
Among this extensive line-up, we are pleased to introduce the LEICA DG VARIO-ELMARIT 12–60 mm F2.8–4.0 ASPH. POWER O.I.S. (referred to hereafter as this lens). This is the second LEICA DG zoom lens to be developed for the standard 12–60 mm range.
To begin, I would like to talk about the time when this lens was first considered during development discussions.
Looking back to those early days, when we were debating "the lenses of the future", I remember feeling a little perplexed when the product planning team first proposed this lens as a development candidate.
・We already have a comprehensive line-up of standard zooms, so why add another one?
・And another 12–60 mm? With the Sanhangoroku already in the range*, how could we possibly differentiate it?
*The LUMIX G VARIO 12–60 mm F3.5–5.6 ASPH. POWER O.I.S., the first 12–60 mm lens to be developed.
The discussion became lively, full of surprise and intensity.
Then the next words from the product planning team pushed things even further:
"What if it were a zoom lens for the LEICA DG series?"
Hearing that, I could broadly see the direction they were aiming, but my first impression was still, “This will be difficult”.
Even so, countless ideas began to flash through my mind.
If the lens were to carry the LEICA name, we could demonstrate higher levels of quality and more advanced technology, whether in the f-stop or optical performance. So the question became: how could we evolve from the previous-generation LUMIX G VARIO 12–60 mm F3.5–5.6 ASPH. POWER O.I.S.?
Looking back at the designs of the lenses we had developed so far, we began to sketch out how this new lens should be configured.
As a matter of fundamentals, a constant F2.8 aperture inevitably results in a larger lens. By contrast, a constant F4 aperture allows for a more compact design, although many users had voiced the desire for a lower f-stop.
A high-performance lens that keeps size under control while still offering a lower f-stop. The challenge was set!
After much deliberation on how to meet these demanding requirements, the concept of the F2.8–4.0 lens was born. As the specifications gradually took shape, the necessity and guiding concept behind its development also became clear.
The vision was to create a series of three LEICA-branded zoom lenses, beginning with this model and followed by two others, so that the entire range from ultra-wide angle to ultra-telephoto (with teleconverter support) could be covered under the LEICA name.
The other two lenses are the wide-angle zoom LEICA DG VARIO-ELMARIT 8–18 mm F2.8–4.0 ASPH. and the telephoto zoom LEICA DG VARIO-ELMARIT 50–200 mm F2.8–4.0 ASPH. POWER O.I.S.
This series of lenses makes it possible to build a compact, lightweight system that takes full advantage of the Micro Four Thirds format. Even when carrying all three lenses, mobility remains high, and they deliver beautiful, expressive power worthy of the LEICA name.
This lens was developed as the first in a series embodying this concept.
As we mentioned in our article "This is the Optical Design Department: Second Edition [LUMIX S PRO 24–70 mm F2.8]", large-aperture zoom lenses are extremely popular. Manufacturers offer a wide variety of well-established models in this zoom range, differing in focal length, f-stop, size, and other specifications.
What features should be incorporated when designing a new large-aperture zoom lens for the Micro Four Thirds system? How can we build on the system’s hallmark strengths of compactness and lightness, while also giving the new lens its own unique advantages?
Although such development work may feel exciting at first, it soon becomes clear how difficult it is to chart a path to realisation.
In practice, the design process required us to continually identify and resolve the challenges posed by the new specifications.
Compared to its predecessor, the LUMIX G VARIO 12–60 mm F3.5–5.6 ASPH. POWER O.I.S., this lens has not only received LEICA certification, but also boasts enhanced image stabilisation and 4K video capability. These features further broaden the range of shooting scenarios it can handle.
The New Standard Zoom Lens for LUMIX: Key Evolution Points
This section introduces some of the key features that expand the range of shooting scenarios this lens can handle.
While user-friendly standard zoom lenses are already available, this lens was designed to exceed expectations by offering superior performance and high quality to customers seeking the best possible results.
During the design process, we held repeated discussions to explore ways of enhancing its market appeal. This made for a demanding development journey, but looking back, it remains a rewarding experience.
The three main areas of evolution are:
・LEICA certified
・Enhanced image stabilisation
・4K video capability
All of these features were incorporated and refined into a single lens during the optical design process.
While this is not unique to this lens, the technologies of optics, mechanics, and control were advanced in parallel during the development process.
In the field of optical design, simulations are revised time and again as functions and requirements become clearer, or as individual elements are further refined.
This lens was designed to perfection. It particularly required frequent revisions to its design simulation.
With that in mind, let us now look at each of the key points of evolution in detail.
LEICA Certified
LEICA certification was part of the specification from the very beginning and represents a clear step forward from the existing LUMIX G VARIO 12–60 mm F3.5–5.6 ASPH. POWER O.I.S.
However, optical design is a process of optimisation.
Even if the criteria for LEICA certification are met at one stage, the balance can easily be lost when new specifications are added, and the design may once again fall short of the required standards.
Ultimately, the optical configuration is refined by incorporating key specifications in a sophisticated manner through the careful placement of aspherical and ED lenses.
For this standard zoom lens, the first group, which includes the front element, was constructed from three lenses to suppress axial chromatic aberration, which tends to occur more readily at the telephoto end.
While longer telephoto zooms typically use anomalous dispersion glass to suppress chromatic aberration, this lens, with a 35 mm equivalent focal length of 120 mm, required a different approach. Taking into account both the machinability of the lens shape and the specific gravity of the material, we opted for a lens material with characteristics close to what optical designers call anomalous dispersion glass, but with the added benefit of being lighter in weight.
In addition, aspherical lenses were placed in the second, third, and fourth groups to minimise aberration fluctuations during zooming.
Lens configuration
In particular, the third lens group contains two aspherical lenses. The front element minimises spherical aberration, while the lens closer to the image sensor reduces aberrations at the edges of the image.
To obtain LEICA certification, aberrations had to be minimised and performance enhanced. This also required a larger aperture to meet the core specification requirements. Inevitably, the higher performance and larger aperture demanded by LEICA certification also resulted in a larger lens diameter.
For the design of this lens, we drew on our expertise gained from the LUMIX G VARIO 12–60 mm F3.5–5.6 ASPH. POWER O.I.S., which had already achieved a highly compact form. The basic configuration was therefore based on the layout of the F3.5–5.6 model.
That said, not everything could be carried over directly, and certain areas were refined specifically for this lens. Notably, the image stabilisation lens group was redesigned and repositioned to allow for a more compact design, while also incorporating new specifications to enhance correction performance.
One common optical design approach for achieving high performance in a compact, easy-to-handle size is the use of glass materials with a high refractive index. However, such materials tend to cause uneven transmission across different wavelengths. For this reason, we used high-refractive-index glass only where appropriate, carefully considering its effect on overall light transmission.
I believe the result is a lens that renders colours naturally and faithfully, without introducing any unusual colour tones.
The optical configuration design takes into account the placement of each lens element, the lens mounts, and the positioning of the drive components. Furthermore, the range of movement during zooming and focusing is considered when determining the light transmission path to ensure the lens elements are not unnecessarily large.
G99D,LEICA DG 12-60 F2.8-4.0 / 54mm,1/250sec,F5,ISO200
Enhanced Image Stabilisation: Dual I.S.2
There are various methods of image stabilisation, but during the development of this lens our focus was on Dual I.S.2, an advanced version of the Dual I.S. system that integrates O.I.S. and IBIS.
In this system, O.I.S. determines the specifications of the lens elements inside the barrel that perform stabilisation, while IBIS defines the design parameters based on the movement of the image sensor.
The evaluation of Dual I.S.2 coincided with the finalisation of the optical design data.
Despite the fast-approaching deadline for the lens design, we managed to finalise the specifications and incorporate them into the lens.
For this article, I took a number of test shots and could clearly feel the effect of the image stabilisation. I usually keep image stabilisation switched on, but to provide a point of comparison, I took some shots in a park, focusing on a low-lying object. The subject was 30 cm tall and I photographed it from a distance of 1 m, deliberately choosing a dimly lit environment to experience the effect more fully. Please note that this required the use of a larger f-stop.
G99D,LEICA DG 12-60 F2.8-4.0 / 60mm,1sec,F22,ISO200
4K Video Capability
The 4K video capability of this lens relates to both focusing and image stabilisation. Since image stabilisation has already been covered, this section will centre on focusing.
When searching for the peak of focus on a subject, the angle of view can sometimes shift. In this lens, that change has been reduced to an absolute minimum during autofocus operation while shooting 4K video.
This minimisation is achieved through a combination of sophisticated optical design and precise control of the focus lens and drive mechanism.
During AF operation, the focusing lens moves, which alters the angle of the incoming light and the height at which the light exits the lens. The smaller these changes, the less variation there is in the angle of view.
The optical design process involved determining the optimal placement of the focusing lens to minimise changes in the angle of view. Thanks to our experience in developing many lenses optimised for video recording, we were already familiar with the focusing specifications required for LUMIX lenses.
However, achieving 4K video compatibility required further minimisation of changes in the angle of view.
For this reason, the shape and movement of the focusing lens were carefully adjusted at the design stage to ensure full 4K compatibility.
Handling and Operation
The movement of the lens elements within the barrel when zooming must also be considered in the optical design. With this lens, the overall barrel length remains virtually unchanged at the wide-angle end, even when the focal length is altered.
Although lens movement is governed by the cam mechanism, we have fine-tuned the movement of all zoom elements to ensure smooth operation all the way to the telephoto end within the constraints of the optical design.
Some may wonder, "Does the movement of lens elements when turning the zoom ring affect photography?" In practice, the feel of rotating the zoom ring is part of the lens’s character.
We hope you will try it for yourself.
Editor's note:
When turning the zoom ring, it felt perfectly calibrated. It was neither too tight nor too loose, and it moved smoothly into position. This finely tuned torque undoubtedly enhances the shooting experience with this lens. Alongside its specifications and optical performance, this tactile feedback adds to the lens’s unique character.
G99D,LEICA DG 12-60 F2.8-4.0 / 25mm,1/6400sec,F3.5,ISO800
G99D,LEICA DG 12-60 F2.8-4.0 / 32mm,1/400sec,F8,ISO200
G99D,LEICA DG 12-60 F2.8-4.0 / 32mm,1/400sec,F8,ISO200
Lastly
This article has provided an overview of the optical design of the LEICA DG VARIO-ELMARIT 12–60 mm F2.8–4.0 ASPH. POWER O.I.S.
Thank you very much for choosing to read about this lens among so many others.
We will continue to introduce lenses that embody LUMIX’s dedication to detail and craftsmanship.
There are still many lenses we are eager to talk about! Stay tuned for the next article!