D FA-series lenses   Lenses are the dream and pride of the optical manufacturer

Lens quality should be decided strictly by the imaging power

During the age of film photography, the rendition of a photograph genuinely depended on the lens used. It was a time where there was no place for deception. Lenses were subject to unforgiving scrutiny, and those winning high evaluation were praised as treasures or masterpieces.

With the arrival of digital photography, this became somewhat complicated because of advancements in image-processing technology. Today’s cameras can effectively compensate for the lens’s optical performance. Even inferior lenses have their place in the market, although they are clearly designed with camera compensation in mind. In the midst of these trends, how did PENTAX design its D FA-series lenses?

“The PENTAX lens development policy has an unwritten rule that we won’t rely on image processing technology,” says a leader of the PENTAX optical design team. “The image desired by the photographer must be produced by the lens, with any remaining aberrations expected ones. We design with considerable respect for the distinctive character and flavor of the individual lens.”

At PENTAX, for instance, a lens might be intentionally designed to leave some spherical aberration, so it will produce a soft visual effect with an open aperture, then become gradually sharper with smaller apertures. Another lens might be designed with a priority on sharpness, so it can produce crisp images even with an open aperture. The lens design team sets out the specific character of each lens first, then designs to reach these goals by optimizing the optical construction and controlling aberrations.

The PENTAX approach is that the choice of the camera’s optical compensation is left to the user. This means that PENTAX simply must design a lens that has solid specifications, then save image processing technology for other sensitive issues. This is true even for the latest D FA-series lenses.

The D FA series is based on the exceptional optical performance of the DA series

PENTAX uses the same lens mount for both APS-C and 35mm full-frame formats. In the case of the full-frame format, PENTAX accumulated a wide range of experience and expertise through the development of the FA-series of lenses during the days of film photography. Despite this, PENTAX decided that the optical performance of new D FA-series lenses should instead be based on that of the DA series, rather the FA series.

“The DA series was designed to not merely eliminate the flares and ghost images that are unique to digital photography, but the assessment standards of the series were set much higher than those of the FA series,” says a PENTAX optics designer. “A digital image is subjected to the most stringent scrutiny even at the edges, because the photographer can later enlarge it to their desired size. We designed the D FA series by applying the stringent standards of the DA series to the 35mm full-frame format, even though we could have lowered these standards at the edges.”

This designer wouldn’t compromise, because he was envisioning the future of lens development. How much more advanced will cameras be in the future? Will there be any difference in image assessment standards? If he could design a lens that would be eagerly used by photographers for many years to come, he naturally would want to choose higher standards.

However, the DA series primarily uses the center of the full-frame image sensor’s circle — the area that guarantees the best optical performance — to achieve its exceptional imaging performance. It was far more difficult to expand this area for the new D FA series to accommodate the full-frame format, than it was when designing the original DA series for the smaller APS-C format.

“To minimize the level of vignetting at the edges of the image, a D FA-series lens must be designed considerably larger that its DA-series counterpart, because the incoming light must reach every corner of the larger image sensor,” the optics designer says. “But it isn’t the PENTAX style to avoid this problem by thinking first about the camera’s image processing technology while we are designing the lens. There are times when we discuss acceptable focal lengths and the reasonable characteristics of certain lenses with the product planning team. But in the end, we always work to design the most advanced optical units.”

Today, a greater variety of aspherical lenses are available to optics designers, because their spherical precision has been greatly improved, and thinner versions are appearing on the market. Special types of glass material are available for large-diameter lenses. Optics designers can make the best use of these recent developments to optimize the imaging power of new lenses. The only problem that then remains is how to mass-produce them.

The key is to create an effective development process

The development of the new D FA-series lenses also meant new challenges in the mechanical design and mass production processes. Some types of glass material are harder to process than others; thinner lenses require higher precision in the polishing and assembly processes. In fact, some of the new D FA-series lenses couldn’t be produced by the existing mass-production system.

One of the designers in charge of developing the lens barrel and inner mechanisms gives the example of one large-aperture telephoto zoom lens. “When I created a test sample that was true to the original design plan, it produced a peculiar flare and couldn’t deliver the resolution we wanted,” he says. “When I looked into the causes, it turned out that the spherical precision of the large-aperture, special-glass lens was slightly off. The error was beyond the level detectable by measuring instruments, so it was impossible for us to anticipate this in advance.”

Under normal circumstances, there was the possibility that the optical design could be redone from the initial design stage. However, the PENTAX optical design team carefully examined the entire production system to find out how, at what point and by what standards they should measure the lens to attain the desired level of precision, and achieve the intended optical performance. Collaborating with the production staff, they reworked the entire assembly line to solve the problem. Because of this experience, the optical design team reviewed the entire development process and implemented a new system. In this system, test models using special glass materials would be polished and assembled from the earliest stages exactly as actual lenses would be mass-produced at the factory.

This was something of an extreme case, but the optical design team also adopted a more elaborate quality-control system for all other D FA-series lenses than the previous one. In the end, the new D FA series even helped advance the company’s development and mass-production processes.

PENTAX must help the user to regain the pleasure of playing with lenses

It’s common practice in the camera industry to divide a lens lineup into flagship models and popular versions, based on optical performance and durability. However, PENTAX has a different way of categorizing its lenses. Although it does offer the high-grade Star series of lenses, some PENTAX enthusiasts claim that the Star series models are the best lenses available, while others insist that the Limited series lenses are more perfectly designed for picture-taking. In other words, PENTAX divides its lenses into different series based on distinctive characteristics, rather than rankings based on specifications. This is because PENTAX wants photographers to take notice of the specific image description of each lens, and find the enjoyment of making the best use of it. That’s how PENTAX built its lens lineup.

“Today, we are developing the D FA-series lenses by listening to the opinions and suggestions of our users, and making whatever changes and improvements we can at the moment,” says the optics designer. “However, in the future we hope to build a more comprehensive lineup that allows users to select a lens based on the type of image description they want, just like a distinction between the Star series and the Limited series. It would also be interesting to design a lens that produces a particularly sharp image at a certain focal range, while yielding above-average image description from the minimum focusing distance to infinity.”

Although it may be some time before this kind of lens is actually developed, there is another way for users to satisfy their love of and pleasure in lenses — through the FA-series lenses. Of course, they aren’t equal to their D FA-series counterparts in terms of image resolution, since some of them may have greater vignetting at the edges, or suffer from flare. However, says the leader of the lens development team, “Many PENTAX users are quite knowledgeable about photographic skills. I’m sure they can find a way to make effective use of these lenses, such as closing down the aperture or changing the camera angle.” There are also photographers who were highly moved by the photographic masterpieces of the past, and are affected by the photographic techniques used in the pictures. Many photographers seek lenses that will produce the tunnel effect created by vignetting at the image’s edges, and the flare effect. Such distinct visual expression can be achieved with FA-series lenses, rather than D FA-series models. The feeling of image rendition and visual expression varies from one photographer to another. That’s why the PENTAX lens designers often reject general assumptions of what a lens should be.

In the spring of 2016, quite a few PENTAX enthusiasts voiced their pleasure at the PENTAX K-1’s launch event, with some saying that they had saved their FA-series lenses just for this new 35mm full-frame camera. Some even brought their favorite FA-series lenses with them to the event to take test shots. Every photographer probably has an unforgettable or irreplaceable lens. The PENTAX K-1 is the camera that can inspire new life in these lenses.

The PENTAX lens designers put all their expertise and passion into the development of every single lens. When photographers are captivated by a lens’s image rendition, it inspires creativity in them, and motivates them to take up their camera and actually use the lens. They discover a totally new world through the lens, and savor the joy and excitement provided by it.

In photography’s earliest days, cameras and lenses were created purely for this purpose. Believing that this still holds true today, and will remain so in the future, the PENTAX lens development team has created the D FA-series of lenses for PENTAX enthusiasts across the globe.