Episode 7: The 24-70mm F2.8 DG DN | Art

In December 2019, SIGMA released the large-aperture standard zoom lens 24-70mm F2.8 DG DN | Art for use with mirrorless cameras. 24-70mm F2.8 standard zoom lenses, with the brightness and angles of view they offer, have already become a staple lens for many photographers. Lenses with these specs, however, are among the most difficult lenses to create of all lenses for single-lens reflex cameras.
In this column, I would like to speak a little about the special characteristics of the 24-70mm F2.8 DG DN | Art and the difference between manufacturing lenses for single lens reflex cameras and for mirrorless cameras.

“Nothing ventured, nothing gained.” – a curse and a blessing

First, let me begin by outlining the development background of the 24-70mm F2.8 DG OS HSM | Art.

With the start of the SIGMA GLOBAL VISION in 2012, SIGMA’s lens catalogue was divided into the three categories Art, Sports and Contemporary, with many new lenses having been released since then. Especially the large-aperture prime lenses of the Art series have been very popular with customers thanks to their excellent optical qualities.
However, the success of the Art lenses actually made the development of large-aperture standard zoom lenses more difficult. SIGMA categorized zoom lenses with these specs in the Art line, but creating a zoom lens with the stellar optical performance customers have come to expect of Art lenses proved challenging. Standard zoom lenses of this caliber are created by utilizing the absolute highest-end manufacturing technologies each lens maker has at their disposal – a true “Nothing ventured, nothing gained” approach. Outperforming the competition was not an easy task.

In February 2017, SIGMA eventually released the 24-70mm F2.8 DG OS HSM | Art. It was a lens that satisfied in performance, quality and size, but its brilliant specs came at the cost of a weight of more than 1kg. The inside of this lens was very crammed with HSM (hyper-sonic motor) auto-focus and full-time manual override, internal-focusing cam mechanism, and OS mechanisms etc. using up all available space.

The “Nothing ventured, nothing gained” approach would necessarily result in tightly crammed lenses and this idea has been largely accepted by all lens manufacturers. SIGMA’s 24-70mm F2.8 DG OS HSM | Art was no exception, as we too strived for the highest possible optical performance and build quality. A large-aperture standard zoom lens for single lens reflex cameras simply isn’t a casual lens to take with you on walks.

The mirrorless revolution

While large-aperture standard zoom lenses for single lens reflex cameras became ever larger in their quest for better performance, there was a revolution taking place in the market: the emergence of mirrorless cameras.
In 2008, Panasonic released the LUMIX DMC-G1 (or “G1”) as the world’s first mirrorless camera. The G1 realized a short flange back by doing away with the instant return mirror of (D)SLR cameras, thereby greatly increasing the freedom lens makers were allowed in their optical designs, especially in the wide-angle and standard range.
This was not the only factor brought about by the mirrorless revolution for lens designs, though. The design of the LUMIX G VARIO 14-45mm/F3.5-5.6 ASPH./MEGA O.I.S., which went on sale at the same time as the G1, did not simply rely on the short flange back alone. Its focusing drive was powered by a stepping motor, and focus scale abandoned in favor of an electric focus-by-wire manual focus ring. Furthermore, instead of relying on a cam mechanism to compensate for the focusing lens’ changing position when zooming, the design opted for a software-driven motor system. As a result, full-time manual mechanisms and internal-focusing cam mechanism were now redundant, and the inner structure of lenses became much simpler.
In a certain way, this lens has changed the history of interchangeable lenses. I still remember the earnest surprise and glee that I felt when I first took this lens apart.

Panasonic LUMIX DMC-G1 and LUMIX G VARIO 14-45mm/F3.5-5.6 ASPH./MEGA O.I.S.
Photo by Yasuhiro Ohsone

Compact and high performance: the 24-70mm F2.8 DG DN | Art

Here we return to the subject of the column.
As a modern large-aperture standard zoom lens, the SIGMA 24-70mm F2.8 DG DN | Art owes its existence to the mirrorless revolution. Like the 14-24mm F2.8 DG DN | Art lens that we released in September 2019, this lens was designed to make full use of the technological advances brought about by mirrorless design:

  1. Tremendously increased freedom for the optical design due to the short flange back
  2. Focus-by-wire system instead of full-time manual mechanism
  3. Great reduction in internal cam parts thanks to software-driven AF motor system
  4. The adoption of a stepping motor for the AF drive allows smooth AF-C and AF for video recordings. It also increases the freedom for the mechanical structure design
  5. Leaving distortion correction and vignetting reduction to the camera’s image processing allows us to focus on a higher effectiveness of other optical corrections and have more liberty in our optical design

By leaving distortion correction and vignetting reduction to the camera’s image processing, we gained more freedom in our optical design and could focus on higher effectiveness of other corrections

Thanks to these five innovations, the 24-70mm F2.8 DG DN | Art improved its optical performance tremendously compared to older single lens reflex models while achieving a compact size for a large-diameter standard zoom lens.
Please have a look at the MTF graph below.

The optical performance of the 24-70mm F2.8 DG OS HSM | Art for use with single lens reflex cameras already is extremely high. But the newer 24-70mm F2.8 DG DN | Art for mirrorless cameras clearly surpasses its optical qualities. The improvements of the peripheral chromatic aberrations and the astigmatism, in particular, are remarkable.
Thanks to the simpler lens design, we also managed to reduce the weight of the lens, from 1,020g of the (SIGMA-mount) single lens reflex model to a mere 835g of the 24-70mm F2.8 DG DN | Art (L-Mount version).
The 24-70mm F2.8 DG DN | Art not only excels in optical performance, it also became a much lighter lens.

24-70mm F2.8 DG DN | Art(left) and 14-24mm F2.8 DG DN | Art(right)

A flagship lens for the mirrorless era

With its many achievements thanks to its exclusive design for mirrorless cameras , the 24-70mm F2.8 DG DN | Art could be considered the perfect product for the mirrorless era. However, it would be mistaken that all its accomplishments were simply achieved by adapting to the mirrorless camera system. In fact, we began exploring lenses for mirrorless cameras very shortly after mirrorless cameras entered the market in 2008, and it is the accumulated know-how from constant research that enabled us to develop a lens that combines high optical performance with a compact size and weight.
While we worked on simplifying the lens design, the quality of the lens barrel – especially the smooth zoom and manual focusing rings as well as the rigid material – have steadily improved. I would be delighted if you found the chance to experience the feel of the lens and its zoom and focusing rings in a camera store sometime.
With its extremely high optical performance and its exceptional build quality, the 24-70mm F2.8 DG DN | Art is ready to be one of SIGMA’s flagship lenses for the mirrorless era.

Yasuhiro Ohsone

Head of product planning at SIGMA

Entered SIGMA in 1987. Has worked in the development of optics and mechanisms as well as collaborating with many companies. Became head of product planning in 2013.

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