Episode 10: Ultra Telephoto Lenses
– Ultrasonic Motors, Zoom, and the Mirrorless Revolution

In the previous column, “Episode 9: Ultra-Telephoto Lenses – The Era of Auto-focus and Special Low-Dispersion Glass,” I continued the story about SIGMA’s development of ultra-telephoto lenses. SIGMA had successfully mass-produced in SLD glass (Super Lowispersion glass) and achieved a remarkable reduction of chromatic aberrations. However, in a wave of autofocus in the industry, we had been confronting new and difficult challenges in boosting the AF speed and performance on our ultra-telephoto lenses.

Fast autofocus – a difficult goal

In 1992, SIGMA released the APO 800mm F5.6 and the APO 1000mm F8, two high-performance ultra-telephoto lenses that made use of SLD glass.
However, the AF driven by the DC motor built in the camera (DC motor built in the lens side for EOS) and the reduction gear made a loud operating noise and the response was not good. Our lens was unlikely to outpace the lenses utilizing Canon’s USM (Ultrasonic motor) in both speed and quality.

Late SIGMA president Michihiro Yamaki summarized the difference pointedly as, “Our lenses are loud and slow, while Canon’s do the job quick as a flash.”.

Ultrasonic motors

At this point, I would like to introduce two important companies: SHINSEI CORPORATION and FUKOKU Co.,LTD.
SHINSEI CORPORATION’s Toshio Sashida is the inventor of the Ultrasonic Motor. The mechanism of an ultrasonic motor is to apply a high-frequency voltage to a unit called a stator in which a ceramic is attached to a metal ring to generate ultrasonic vibration, and the rotor is rotated by the wave (travelling wave) of the vibration. These motors were groundbreaking – motors that make use of anything but the magnetic forceーthat had not been applied before. However, these motors faced a number of issues in the early stage. One big problem concerned was the precision and the friction of the contact points between the stators that generate the travelling waves, and the rotors, the actual rotating parts. This slightest imprecision, or the tiniest foreign objects, would cause disturbing sounds and even cause stators and rotors to stop moving. Sashida was able to find a solution for these problems by adding “sliders” – a friction material – between rotors and stators. The company asked to manufacture these slider materials was FUKOKU Co.,LTD.

FUKOKU Co., LTD. (hereinafter referred to as FUKOKU) is a manufacturer of rubber and seals holding the largest share of automobile wiper blades in the world. As the slider material needed to be both elastic and have high friction in order to transfer micro-vibrations generated by the travelling waves, Sashida considered rubber the best choice and decided to approach FUKOKU regarding manufacturing, as FUKOKU also possessed strong vibration analysis technology that would prove advantageous. FUKOKU agreed with SHINSEI CORPORATION’s request, but rather than only supplying the slider materials, FUKOKU stated they would prefer handling the complete manufacture of ultrasonic motors instead.

Developing ultrasonic motors

In 1994, Michihiro Yamaki approached FUKOKU for ultrasonic motors co-development for interchangeable lenses. As FUKOKU had already succeeded in developing and mass-producing ultrasonic motors, the big challenge of developing ultrasonic motors for interchangeable lenses involved finding the optimal output, control and interlocking mechanisms and solutions for integrating the motors in the lens.
Aiming to complete the ultrasonic motor drive and control, , SIGMA added an ultrasonic motor to the 1995 edition APO TELE MACRO 400mm F5.6 for Canon EOS- and SIGMA SA-mount in 1996 and presented it as a prototype at Photokina 1996. On this occasion, this ultrasonic motors co-developed with FUKOKU, were given an exclusive nameー“HSM” (Hyper Sonic Motor).


Following Canon and Nikon, SIGMA unveiling its development of ultrasonic motors caused a large impact in the industry. Yet, there still was a mountain of problems to be solved. Regarding the drive of the ultrasonic motor, SIGMA’s electronic and software division, which has a lot of experience with AF, exerted its abilities, and with the support from FUKOKU, development proceeded smoothly. However, the mechanical design division could not create a satisfactory interlocking mechanism. But problems remained not only regarding the interlocking of the ultrasonic motors but also regarding methods of integrating them into the lens. The ultrasonic motors created annoying sounds at the slightest disturbance when driving the focus lens element – getting rid of these creaky sounds was proved difficult to the development team.

In short, these prototype lenses presented at the 1996 Photokina were not considered for production at all – they were “makeshift” lenses driven by suppression of annoying sound reduction. It had taken the mechanical design division another half year before they successfully developed a suitable interlocking mechanism and got rid of any unwanted sounds.
The SIGMA APO TELE MACRO 400mm F5.6 HSM was finally ready to be released in 1997.

Rapid progress of HSM

The APO TELE MACRO 400mm F5.6 HSM has surprised the market. In many respects, however, the lens was still an “advanced prototype”. It was not a product destined to generate a large number of sales, owing in part to its price-tag of ¥145,000 (about $1,300) – relatively high for a prime lens in the 400mm F5.6 category.

With the release of the APO 70-200mm F2.8 EX HSM in 1998, SIGMA had succeeded in mass-manufacturing HSM-equipped lenses. As I wrote in episode 2 of “Ohsone’s Anecdotes,” the lens became a huge hit that boosted both SIGMA’s HSM production as well as the popularity of the EX series. The number of HSM-equipped lenses increased rapidly after the release of this lens, thanks to SIGMA’s improved development capabilities. The rapid release of ultra-telephoto lenses alone (excluding all other lens categories) in this time period is extraordinary :

Left: APO 300mm F2.8 EX HSM (1999), Middle: APO 500mm F4.5 EX HSM (1999), Right: APO 800mm F5.6 EX HSM (1999)
Left: APO 50-500mm F4-6.3 EX RF HSM (2000), Middle: APO 120-300mm F2.8 EX IF HSM (2002), Right: APO 300-800mm F5.6 EX IF HSM (2003)

The Hyper Sonic Motors contributed exceptional improvements to the AF performances. The AF speed – the time until the subject is in focus – made remarkable jumps, so did the accuracy, and there was almost no audible sound during autofocusing either. Michihiro Yamaki’s vision of “making the job quick as a flash” had been realized. As the reputation of the EX series lenses rose, the higher price-tag due to using both special low-dispersion glass and ultrasonic motors soon became more and more accepted.

The challenges for AF ultra-telephoto zoom

Let’s take a look at ultra-telephoto zooms as well. As I wrote in episode 9 of “Ohsone’s Anecdotes,” SIGMA released the SIGMA APO ZOOMτ 100-500mm F5.6-8 and the SIGMA APO ZOOMω 350-1200mm F11 one after the other in 1986. Both were high-performance lenses that made use of SLD glass but adding AF functionality meant that we have more problems to confront. There is the dark F-stop, of course, but more significant problems lay in the design of telephoto lenses and ultra-telephoto lenses at the time: the focusing mechanism relied entirely on the first lens group at the front of the lens. Moving these large and heavy lens elements with AF motors was unrealistic – for such zoom lenses, it was crucial to design an inner focusing mechanism.
But inner focusing mechanisms for zoom lenses still needed to overcome another huge design hurdle at the time: whenever the focal distance was changed (zooming in or out), the focus lens element had to be moved accordingly to avoid being out of focus.
SIGMA eventually solved this problem and with the release of the 28-105mm F4-5.6 UC ZEN in 1993 realized a zoom lens with an inner focusing mechanism. However, before inner focusing mechanisms could also be applied to ultra-telephoto zoom lenses, a new calculation program, as well as numerous specialized cam mechanisms, still needed to be designed.

The first company to realize an ultra-telephoto zoom lens with inner focusing mechanism was TAMRON, when they released their SP 200-400mm F5.6 IF lens in 1994.

SP 200-400mm F5.6 IF
Photo: SEIN Online

At the time SIGMA experimented with new structures for inner focusing mechanisms inspired by Canon’s EF 35-350mm F3.5-5.6 L and subsequently began developing inner focusing technology for ultra-telephoto lenses. In other words, in this period SIGMA not only tried to develop the ultrasonic motors but also an inner focusing mechanism into its ultra-telephoto lenses.

The ultra-telephoto zoom pair

At the PMA (an American camera trade show) in February 1996, SIGMA was ready to unveil the APO 135-400mm F4.5-5.6 ASPHERICAL RF, our very first ultra-telephoto lens with AF, thanks to a new inner focusing cam structure.
The reactions were impressively positive, but at this time the late company president Michihiro Yamaki had a surprising idea: “Wouldn’t it be possible to change only the first three lens elements of the 135-400mm’s design in order to reach a focal length of 500mm?” More surprisingly, the answer from the optical design team was, “Yes, it’s possible!”
And just like that, one more ultra-telephoto zoom lens – the APO 170-500mm F5-6.3 ASPHERICAL RF – was born and released alongside the 135-400mm in 1996. These two AF-enabled ultra-telephoto zoom lenses were successful beyond expectations. They became SIGMA’s major products.

APO 135-400mm F4.5-5.6 ASPHERICAL RF
APO 170-500mm F5-6.3 ASPHERICAL RF

After that, the lineup of SIGMA’s AF super-telephoto zoom became the so-called “3 top” with the addition of the APO 50-500mm F4.5-6.3 EX RF HSM that I wrote in Chapter 1.

Era of the ultra-telephoto zoom

Due to the huge success of ultra-telephoto zoom lenses, SIGMA’s development of prime ultra-telephoto lenses has slowed down since 2000. The launch of SGV (SIGMA Global Vision) in 2012 did little to change this situation. Only one single prime lens, the 500mm F4 DG OS HSM | Sports, has been released since then. The lens sits at the absolute peak of optical performance and AF capabilities, far beyond any zoom lenses, but it is hard to see tangible result points towards a clear shift of interest towards ultra-telephoto zoom lenses.

ultra-telephoto zooms in the mirrorless era

I would like to conclude this series with a brief look at ultra-telephoto lenses in the mirrorless era.
When I researched lenses created for the micro four-thirds standards from the early days of mirrorless cameras, I was surprised by the precision of their AF as well as the lightness and small size of the focus lens elements. How great would it be to achieve these same traits for full-size ultra-telephoto lenses or large-diameter lenses, I wondered.
Luckily, all of the eleven AF-enabled ultra-telephoto lenses that SIGMA has developed employ an inner focusing mechanism; we have done thorough research on optical designs that rely on the small lenses of the rear lens group for focusing.

The last lens I want to introduce in this series is the 100-400mm F5-6.3 DG DN OS | Contemporary, SIGMA’s latest ultra-telephoto zoom lens for mirrorless cameras. The lens features the best optical performance of an ultra-telephoto zoom lens in SIGMA’s history, manufactured at a size that fits the compactness of mirrorless cameras. And because the light focusing lens element is moved directly by the motor, the lens works very well with all the latest AF features of mirrorless cameras (such as face-detection and eye-detection AF).

Taken with the 100-400mm F5-6.3 DG DN OS | Contemporary (400mm tele)
Photo: Yasuhiro Ohsone

I will be thrilled if this ultra-telephoto series provokes you to experience the new possibilities created by our mirrorless-era ultra-telephoto lens, and if you remember the rich history of SIGMA ultra-telephoto lenses – introduced in episode 8, 9 and 10 of this column – when you try a 100-400mm F5-6.3 DG DN OS | Contemporary.

Photo: Yasuhiro Ohsone


I have tried to provide a summary of SIGMA ultra-telephoto lenses in the past three articles, but there are still products in this lens category that I could not cover. I especially regret for not featuring the APO 200-500mm F2.8 / 400-1000mm F5.6 EX DG lenses despite the huge interest (I think) in their history – I know I could have talked about them forever.
I look forward to discussing the missing lenses as part of a future episode of “Ohsone’s Anecdotes”. Stay tuned!

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