This is the Optical Design Department- First Edition

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 in the Optical Design Department 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 camera lens, we encourage you to learn more about the design philosophy behind LUMIX lenses, and for those who already own a LUMIX lens, we hope you enjoy learning about the unparalleled attention to detail and thought that goes into the superb image quality you enjoy in your photography.

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 enthusiasm for lens collecting.

The first article is about LUMIX S PRO 50 mm F1.4, explained by Suzuki.

When we released our first two mirrorless interchangeable lens cameras with a full-frame 35 mm image sensor, the DC-S1R (hereinafter S1R) and DC-S1, in 2019, we also released three lenses as the first phase of our lens lineup: the LUMIX S 24-105 mm F4 MACRO O.I.S., the LUMIX S PRO 70-200 mm F4 O.I.S., and the LUMIX S PRO 50 mm F1.4 (hereinafter 50 mm F1.4).

Of these, our mission for the optical design of the 50 mm F1.4 was to create a master lens for the LUMIX full-frame system.

The master lens is the reference lens used to determine the image quality design of the camera. So, I started by asking myself what makes a lens a reference lens.

Defining the LUMIX master lens as one that "faithfully reproduces the scene as seen by the photographer", I gradually established a design concept and identified the following three key indicators.

I believed that we could create the LUMIX master lens by achieving these three key indicators.

Since the S1 series is primarily aimed at professional users in terms of resolution performance, it was necessary to achieve the highest image quality without compromise not only in the camera but also in the lens.

Therefore, we set out to achieve the highest resolution performance ever, including not only the Micro Four Thirds lenses we had previously developed but also existing large-aperture standard lenses. We compared shots taken with a variety of lenses and received feedback from professional photographers throughout the development process.

The high frequency range was particularly challenging in this development. For the S1R, which was being developed at the same time as the 50 mm F1.4, we considered using a high-resolution mode, in which the camera would automatically take eight consecutive shots while shifting the sensor, using the in-body image stabilisation (IBIS) mechanism, and then automatically process the images in the camera. This mode required a resolution equivalent to a maximum of approximately 187 megapixels.

To achieve this resolution performance, it was necessary to ensure a good MTF at higher frequencies than in normal shooting.

Aspherical lenses are the key to good MTF at high frequencies. Aspherical lenses are effective at correcting aberrations, but over-reliance on them can lead to high form error sensitivity, and in manufacturing, they can cause performance variation from lens to lens.

In designing the 50 mm F1.4, we sought to maximize the effectiveness of the aspherical lens by finding the perfect balance between design performance and manufacturing. To this end, we had many heated discussions with the aspherical lens team at the Yamagata factory, which has a long history of producing aspherical lenses.

Yamagata factory that maintains the high quality of LUMIX lenses

We were in the final stages of the design process. When we settled on a design solution, the aspherical lens was placed third from the front element.

The aspherical lens is such a key component that it would not be an exaggeration to say that it is the most important part in achieving the desired image quality. However, after consulting with the aspherical lens team at the Yamagata factory, we were able to arrive at a design solution where the aspherical lens was placed fourth from the subject, which we felt was the best balance between design performance and manufacturing.

Although it was a last-minute change, the development team was able to make the design change in time because of their strong determination to achieve a level of image quality that would satisfy everyone on the development team.
As a result, the lens achieved resolution performance suitable for use as a reference lens. It even achieved a level of performance high enough to withstand high-resolution mode, not just the 30 lp/ mm level published in the MTF curve in the catalogue.

We have extensive knowledge of bokeh from our experience in designing Micro Four Thirds lenses, but since we wanted to rethink bokeh rendering from the ground up, we evaluated various lenses, especially large-aperture single focal length lenses, and found that softening the rear bokeh (bokeh behind the focus position) would make the front bokeh (bokeh in front of the focus position) hard, and vice versa. Therefore, for the master lens, we aimed to create a flat bokeh with no peculiarities in either the rear or front bokeh.

There was some speculation that we should prioritise the rear bokeh since it is the most commonly photographed aspect of bokeh, but we decided that an optical design that prioritised softness in the rear bokeh would result in a trade-off with the aforementioned resolution performance, and that as a master lens we should aim for near aberration-free reproduction, so we decided to aim for flat bokeh.

We also proceeded with the optical design while carefully correcting for aberrations (especially those that pass around the periphery of the lens), from large bokeh such as ball blur, which consists of objects at a large distance from the main subject, to small bokeh, which is a continuous blur from the main subject that is in focus.

As a result, we were able to create a flat and natural bokeh that, combined with the high-resolution performance of the lens, enables expression with a three-dimensional feel that makes the subject stand out.

As a master lens, chromatic aberration is minimised to the extreme to faithfully reproduce the colours of the subject.

When addressing chromatic aberration, we not only considered general axial and lateral chromatic aberration but also focused on the optical design, from false colours like purple fringing, which is easily noticeable when there is a large brightness difference between bright and dark objects such as water

In particular, when selecting glass materials, we pay special attention to the partial dispersion ratio, a parameter that expresses the anomalous dispersion at the short wavelength.

At the early design stage, we select glass materials from a wide range of glass materials, including those from different glass manufacturers. We first select candidates based on a theoretical calculation, and then conduct a detailed design based on a design solution in which chromatic aberration has been perfectly corrected.

By taking these steps, we were able to minimise chromatic aberration without the side effects on various aberrations, including higher-order aberrations, that can occur when chromatic aberration is corrected on an ad hoc basis after the design process is completed.

In addition, some glass materials are custom-ordered to minimise Abbe number variations, thereby minimising manufacturing variations.

Even when I think I have taken a good photo, if I look closely and see colouration in the water droplets in the hair of a child playing in the water, I regret not stopping down the aperture a bit more. However, this 50 mm F1.4 lens has suppressed chromatic aberration even at the widest aperture, so you can enjoy the wide-open image without hesitation.

A masterpiece worthy of a master lens

In addition, we have carefully refined the optical design, focusing on aspects such as controlling image quality at finite distances, thoroughly correcting aberrations in the details of transverse aberrations that cannot be classified as spherical or coma aberrations, and developing new adjustment methods and new inspection methods. The result is a lens with a performance worthy of a master lens.

Before starting the design, we spent more than half a year researching all existing large-aperture lenses, including SLR and mirrorless lenses from our own and other companies, while refining the image reproduction we wanted. This process took much longer than the usual development time.
We came up with more than 200 different design solutions, and our development team believes we have achieved satisfactory image reproduction.

This article has provided an overview of the optical design of the LUMIX S-series Master Lens 50 mm F1.4.

If you already own this lens, we hope you will take note of the bokeh and chromatic aberration described when shooting.

If you do not have this lens, we encourage you to try it and experience the image reproduction of the LUMIX master lens. We remain committed to introducing lenses that showcase LUMIX's meticulous attention to detail.

There are still many lenses we are eager to talk about! Stay tuned for the next article!