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22364_VIC02_E_Cover_V2.indd 1 01.02.2008 11:27:42 Uhr

22364_VIC02_E_T_Lens28.indd 3822364_VIC02_E_T_Lens28.indd 38 04.04.2007 15:55:57 Uhr04.04.2007 15:55:57 Uhr

The tiny gap that once existed in the selection of wide-angle lenses in Hasselblad’s H system has now been filled. Mounted on a film body, the existing HC 3.5/35 will yield an expansive 89-degree angle of view – enough to capture anything from vast scenic views to extreme close-up portraiture with exaggerated proportions. The digital H3D series, however, is affected by a lens factor that alters the perspective of a focal length both when compared to film and 48mm ‘full format’. The digital H3D-22 and -39 – which hold the full-format title – do in fact yield a lens factor of 1.1; and while mod-erate, it will transform the 35mm mentioned above into a hypotheti-cal ‘38.5mm' lens. But 38 millimeters fall short of the extreme 90 degree, or more, angle of view necessary in order to qualify for ‘the big wide open’. The marginally smaller sen-sor of the brand-new H3D-31, by comparison, has a lens factor of 1.3 and is therefore affected similarly.

The newly introduced HCD 4/28 serves to fill that last gap in the lens gamut. Mounted on an H3D-22 or -39, the 28mm opens up to a superb 95-degree angle of view. In 35mm ter-minology this would correspond to a 20mm lens. The H system now meas-sures up to digital 35mm cameras in one of the most important arenas of photography: the wide-angle zone. The new HCD 4/28 safeguards excep-tional picture quality, zero distortion and crisp detail throughout the full image plane – at every range.

SMALL, SOLID, AFFORDABLE

The HCD 4/28 is small, solid and affordable all at once. To some this may come as a surprise. “HCD” hints at the technical trick to which the

28mm owes its compactness. ‘D’ stands for digital and signifies that it works with digital Hasselblad cam-eras only – the new H3D models to be exact. Since most photographers will have converted to digital by now, the fact that the 28mm is designed exclusively for digital operation is less restricting than in recent years. In the end, it is this restriction that raises the photographic reproduc-tion as a whole to a higher level. Per Nordlund talks about this in a com-prehensive interview on page 42.

The 28mm is so wonderfully com-pact precisely because of its limited compatibility, as it focuses only on the smaller image circle of digital sensors. While the 49.1 x 37 mil-limeter size of the sensor (H3D-22 and -39) is not much smaller than the 56 by 42 millimeters of the film frame correcting a 28mm lens for the entire medium format film plane – in spite of what appears to be a negli-gible difference in size – demands a substantially larger lens shell, along with wider, more expensive glass dia-meters. This is the reason why Hassel-blad decided to build a lens for digital sensors only, making the HCD 4/28 the first to be designed specifically for the 48mm full format. Mounted on an analogue body would only result in a reduction of brightness in the image periphery. Digitally, however, the 28mm will fully illuminate the smaller image circle of the sensor.

Once it had been established that the new 28mm lens was to be a digi-tal exclusive, Hasselblad took it one step further, bumping up the lens design with a few digital tweaks and, in doing so, exploiting the potential of the digital medium. Fully aware that it would need DAC to counteract a slightly greater lens distortion than usual, the team of engineers decided to make it their priority to achieve

minimum chromatic aberration and maximum resolution. Any distor-tion was to be corrected digitally. Had the priority been lowest pos-sible distortion, the lens would have turned out substantially more com-plex; bulkier, heavier and pricier. It would have altered the nature of the lens design process. The result – the HCD 4/28 with DAC implemented from the start – is probably a better lens than a hypothetical, DAC-less 28mm could ever be.

DIGITAL DISTORTION CORRECTION

It is worth pointing out that the distortion factor is the HCD 4/28’s only ‘weakness’. In all other disci-plines of photography – when it comes to the chromatic aberration or refining the reproduction in close range, for example – the lens is just as good, if not better than those HC lenses that are already prized for their capacity to deliver immaculate results on film. According to Has-selblad, the HCD 4/28 really only distorts slightly more than the HC 3.5/35 and is still within acceptable limits. Those who persist will find a subtle bend in the viewfinder periph-ery, where otherwise straight lines take on a moderately barrel-shaped distortion; but this will not affect the composition in any way.

Hasselblad moves on to perfect the picture with software, starting with an automated removal of distortion. This happens without the photo-grapher ever noticing and is free of side effects, as the Digital Auto Cor-rection (DAC) is an integral element of the FlexColor software, which he uses to manipulate the picture after the exposure. The digital auto correc-tion removes those very last optical aberrations that are inherent in the

construction of a lens, no matter how scrupulously designed. All HC lenses utilize DAC, but the HCD 4/28 is the first Hasselblad lens to rely on DAC for outstanding picture quality.

For the time being, the digital auto correction resolves two – soon three – typical optical aberrations. The first DAC level has long estab-lished a footing in the image formation sequence and stands for ‘Digital Apo Correction’. It elimi-nates residual chromatic aberrations induced by optical constraints that cannot be avoided, regardless of how zero-tolerance oriented the HC lens designs are. DAC practically eradi-cates the residual purple fringing, occasionally caused by chromatic aberration. The second, recently introduced level of the digital auto correction system counteracts the described inherent distortion of HC lenses. The same principle applies: almost any lens will distort if the conditions are right, causing straight lines in the viewfinder periphery to warp. However, all HC lenses are designed to keep distortion to an absolute minimum, even without the interference of corrective soft-ware. Only the HCD 4/28 finds itself slightly below what is commonly accepted by professionals – for this reason, DAC plays a crucial part in the design process.

Hasselblad intends to launch a third level of correction: DAC III will deal with vignetting, i.e., declining brightness towards the corners of the image. While chromatic aberration and distortion are never welcome, vignetting is a frequently accepted, occasionally even desirable photo-graphic ‘error’. So Hasselblad plans to include a slider for the adjustment of vignetting, allowing the photogra-pher to fully eradicate the peripheral reduction in brightness or, if desired, enhance it. While this FlexColor feature awaits to be integrated, all HC lenses – including the HCD 4/28 – yield very little vignetting as it is, even without DAC. DAC is only ever responsible for that last drop of qual-ity, turning an already great picture into an immaculate one.

The new HCD 4/28 beckons owners of H3D cameras into the realm of extreme wide-angle photography, offering an enormous angle of view of 95 degrees – without being as big a build as it may seem in this picture

The new HCD 4/28 lens in the H series represents Hasselblad’s long-awaited entry into extreme wide-angle photography. This lens – a digital exclusive – was designed with certain digital processes in mind, leading the company through unknown technical territory.

INTO THE BIG WIDE OPEN

39 1/2007

TECHNOLOGY HCD 4/28

BY HANNS W. FRIEDRICHPHOTO: JÜRGEN MÜLLER

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40 1/2007

TECHNOLOGY HCD 4/28

or -39, however, the angle of view expands perceptibly. This is where the new HCD 4/28 lens really comes into its own.

From an outsider’s point of view, it could look as though Hasselblad’s developers were trying to circum-vent the blemishes of their lenses by patching them up with digital band-aids. This couldn’t be further from the truth. The choice to embark upon technologically unfamiliar territory was a conscious one. The promise of a fully integrated digi-tal camera system, in which the numerous components – from lens via camera to digital back – are pro-vided by one company, is now being exploited for the first time ever. The approach is unprecedented amongst digital system cameras, even outside of medium format. All resources were utilized to generate the best picture possible. In the end, the images fea-tured in this spread will abolish any lingering doubt in the HCD 4/28’s ability to lay down a stunning result.

What’s truly great about the HCD 4/28 is that it allows you to forget the technological effort that went into its development, facilitating the same natural and creative handling as all other HC lenses. Its expansive angle of view will capture the vast-ness of a lush landscape and also provide a generous perspective in architectural photography. Indoors it will enable you to expose a broad

view in a very tight space. The lens’s optical performance remains excel-lent at close range and enables you to exaggerate the perspective of an ob-ject placed only 10 centimeters from the front lens element – no extension tubes needed. In other words: the HCD 4/28 finally takes the H system into extreme wide-angle dimensions, producing the excellent reproduc-tion qualities of the H3D models in a photographic discipline that, once upon a time, obliged turning to far inferior camera systems.

HCD 4/28 – AT A GLANCE

1 LENS DESIGN

2 DIGITAL DISTORTION CORRECTION

The optical design of the HCD 4/28 is based on the HC 3.5/35 und consists of 12 lenses in 9 groups. The fact that a slightly higher distortion was ac-cepted (which can easily be removed digitally) has resulted in an unusually compact design for this super-wide angle lens

By allowing the HCD 4/28 a slightly higher distortion, Hassel-blad was able to concentrate on the correction of chromatic aberrations and excellent detail reproduction up to the shortest

distance settings. When uncor-rected, the distortion of the lens is visible (left), but this effect is totally removed by the Digital Auto Correction integrated in the FlexColor software (right)

Hasselblad’s HCD 4/28 is born from a pragmatic approach. Surely they could have developed a 28mm lens capable of dealing with the larger image circle of film; indeed, all optical characteristics could have been carried through within satisfac-tory parameters – even without the digital boost. Having said that, the vast majority of H camera owners has jumped onto the digital bandwagon and would no longer appreciate the effort it would take to concoct such a design. An alternative could have been a large and heavy lens with a bulging front element, a proud price tag and still no absolute, aberration-free guarantee.

WIDE-ANGLE PHOTOGRAPHY WITH THE H3D-31

Hasselblad were probably thinking of H3D-31 owners when the 28mm was designed, as it overcomes the obstacle of the smaller sensor with a bona fide wide-angle. In relation to the larger sensors of the other H3D models, the H3D-31 yields a 1.2 lens factor, or, in relation to film, a 1.3 lens factor. The 28mm lens therefore has a focal length the equivalent of a 36mm lens with an angle of view measuring 89 degrees. This way, purchasers of an H3D-31 also have the chance to dabble in wide-angle photography. Mounted on a H3D-22

Photos: Jürgen HolzenleuchterLocation: Hotel Ku’Damm 101, Berlinwww.kudamm101.com

Indoors, the short focal length of the HCD 4/28 can create a feeling of depth. The lens reproduces de-tail homogenously from the center to the corners of the picture

Thanks to Digital Auto Correction (DAC) the HCD 4/28 keeps dis-tortion to a minimum, generating crisp detail at every range (left)


VICTOR: The HC lenses are being developed in collaboration with Fuji, who also manufactures them. How did this cooperation begin?NORDLUND: When we started the H project we developed several basic lens designs, defining modern types of lenses that would suit the cameraand specifying focal lengths, aper-tures, etc. We established how the lens groups would be arranged, which would move and which would not. In other words, we did a lot of design work before we even initiated a dialogue with a potential manufac-turing partner.BENGTSON: Zeiss, after much con-sideration, originally declined our offer, possibly because they were intensely involved with the develop-ment of lenses for the Contax. But eventually we found a great partner in Fuji, with whom we already shared an excellent working relationship on the Xpan camera system. At first we had to justify why the H system no longer featured Carl Zeiss lenses. The moment people start using the cameras and seeing the results, all doubts were cast aside. It is the person who defines the lens specifi-cations who is important, setting and monitoring the quality standards. At this point I really have to give praise to Fuji: the optical design team is superb; the manufacturing process works flawlessly and the end results are highly satisfying.

VICTOR: Can you estimate how much of the work is done by Fuji and how much by Hasselblad?BENGTSON: The manufacturing process is explained quite simply: we build the shutter here in Gothen-burg; Fuji takes care of all other components, including monitoring the final assembly. We also monitor the lens quality in Gothenburg by regularly checking samples.

digital auto correction of chromatic aberration, distortion or vignetting?BENGTSON: To begin with, DAC will never create a fantastic picture if the lens is mediocre. It merely serves to transform an already great picture into a perfect one. Furthermore, all digital corrections must be kept to a minimum. If we were to use a lens with acute chromatic aberrations, for instance, DAC would never generate a picture quality anything like that of a superior lens design. For the most part we see digital auto correction as an opportunity to perfect a lens that is already great. For the 28mm, how-ever, it meant that we could accept a touch more distortion than usual. This enabled us to gain advantages in other areas of the lens design, something that were not so possible otherwise.NORDLUND: If DAC hadn’t been at the back of our minds we would have invested more in minimising distortion; but this would have also involved setting back other charac-teristics. The lens would have been larger, heavier and more expensive. With a retrofocus design such as the 28mm, the correction of distor-tion would necessitate a giant front lens group. The combination of high performance, compact size and affordable price, which the new 28mm now has, wouldn’t have been possible without DAC. In any case, the distortion is not even that high, only slightly greater than that of the 35mm; but if it weren’t for DAC we wouldn’t accept such a deviance. When you understand what DAC enables without negative outcome, the process changes a little. You approach correction a bit differently.

VICTOR: Did you optically measure the necessary corrections for DAC?BENGTSON: That’s the way how other programs presumably operate for this purpose, but our corrections are based on the exact project data of our lenses. Meanwhile, the cor-rective tables integrated in FlexColor contain over 30,000 individual data sets, where each set corresponds to a combination of aperture, distance, converter and extension tube. I can hardly imagine anyone else putting in as much effort as we have, and even we could only do so because we know all components from front lens to sensor and store all relevant information with every picture.NORDLUND: Finding out the count-less corrective values on the basis of a design and testing them was a tremendous task. It’s almost sad to know that all your effort will be completely unnoticed by the user, as

TECHNOLOGY INTERVIEW

for a company like Hasselblad. We received numerous letters from our customers complaining about the lofty prices of V system lenses. This is not so in the case with the H system. I believe our prices to be fair and when buying a Hasselblad lens, you are shopping for the highest quality, not the lowest price. Few would thank us if we supplied less expensive lenses that also performed less well. In theory we could improve perfor-mance by adding additional lens elements and creating bigger, heavier builds; but this would raise the price considerably. With the HC lenses we were able to met the performance standards which we had established.

VICTOR: How are we to imagine the development of a new lens from con-ception to finish? How long does it take?NORDLUND: The H system was in need of a shorter focal length lens

so the idea of the 28mm was born quickly. First we looked at some of our existing designs for reference and we were able to adopt mechani-cal elements from other lens designs, and to save time and money because we could reuse some of the existing tools in manufacturing. I based the 28mm on the design of the 35mm, more or less, changing and improv-ing some elements I thought were either no longer necessary or needed to be improved. We then sent these ideas to Fuji and exchanged ideas for additional improvements. By partly adopting existing components the 28mm was born really effortlessly. The first fully working prototype was produced in only six months, by comparison, designs that we start from scratch usually take a year to reach that point.

VICTOR: Hold on, you thought some things could be improved? Isn’t the thinking nowadays left up to the computer?NORDLUND: The 35mm was an excellent starting point, and the 28mm was to orient itself in this performance class. By adopting ideas from existing designs we don’t have to redesign absolutely everything, but it still takes the computer time to render what the designer imagines. I probably have the fastest computer in the company, but the optimisa-tion process still requires months of calculation time. It’s a mix between pure mathematics, whereby the com-puter attempts to establish the right glass combinations and lens shapes, and a lot of intuition on behalf of the developer.BENGTSON: Many people have the wrong idea: designing a lens requires more than typing a few digits into an edit field and pressing start. The program demands tight control and concrete operating parameters. It can easily improve and fine-tune an existing design, but the designer is the one with the inspiration.

VICTOR: In what way does the auto-focus influence a lens design?NORDLUND: The tendency is to have fewer and smaller moving lenses for the focusing, since this reduces the moving components. In the HCD 4/28 only the rear lens group is moved for focusing. This method also produces better reproductive performance at close range, which is where the 28mm excels. The speed of focusing is also maximized using this type of internal focusing.

VICTOR: Is it tempting to compen-sate for optical shortcomings with

NORDLUND: It was up to us to spec-ify the tests Fuji was to conduct, as we insist upon highly sophisticated measurements for tight qual-ity control. Our involvement in the development process cannot be estimated so easily. We set the specs, developing key components such as the shutter and differential gearing system for manual- and autofocus control. All lenses are based on these components and generally our par-ticipation varies from lens to lens. In the case of the 28mm lens, for example, I’d say we did 80 per cent of the optical development work here in Gothenburg. Fuji was largely in charge of the fine-tuning. In other cases we are less involved.

VICTOR: How significant is the price of a lens during the planning phase?BENGTSON: It’s significant, but not the most important factor by far. That would be the wrong approach

42 1/2007

VICTOR spoke with Per Nordlund, lens developer, and Ove Bengtson, product manager for H System cameras, about lens design and the new HCD 4/28. From the very beginning, both were involved in the develop-ment of the H system.

“WE’LL CONTINUE TO INVENT”

Per Nordlund, lens developer, and Ove Bengtson, product manager for the H series, share their thoughts in an exclusive interview with VICTOR


everything has been implemented in an automatic process.

VICTOR: The next DAC step is to digitally correct vignetting. Does the 28mm really need this?BENGTSON: Retrofocus lenses are not so much affected by vignetting, though no lens will be entirely free of it, of course. Vignetting is dealt with using a corresponding slider in the software, as sometimes it may not be desirable to correct it; you might even want to amplify the vignetting effect. But no one wants to see color fringes or distortion, which is why we correct them automatically.

VICTOR: How will the optical design of Hasselblad lenses change over the years and what has already changed compared with past models?NORDLUND: What’s changed over the past years is an open access to spe-cial types of glass with very low color dispersion. These were formerly used for tele-photo lenses only and are now implemented in the new 28mm lens. Presumably the optical perfor-mance of standard focal lengths such as the 80mm hasn’t changed much, but in my opinion the performance of modern wide-angles has improved vastly, especially in close range and when it comes to color fringes. It is simply the result of next-generation computer technology and superior types of glass. What we are yet to indulge in are aspheric elements. In the sizes that we need, aspheres remain too expensive; but this will hopefully change. The production is becoming cheaper and the design process is generally loosening up. In some cases one could replace two or three lens elements with one.

VICTOR: What kind of lenses are we to expect in the near future?BENGTSON: We will continue to invent new ideas as long as the photographer continues to have wishes and requirements. People ask for all kinds of things, such as Tilt & Shift lenses or long focal lengths with anti-shake protection. We’ll see what we can do. And, finally, a guiding Hasselblad tradition is not to include technology for the mere sake of having it in our products, but only when it truly makes sense for the photographer. At the moment we’re happy with our lens gamut; it’s somewhat complete, contains no duplicates and should by now – thanks to the new HCD 4/28 – hold something in stock for everyone.

VICTOR: Thank you very much for talking with us.

43 1/2007


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