Zoom lenses spanning the 24-70mm focal length range are popular because they can do almost everything most photographers need a lens to do. On the short end, these lenses work well for interiors and scenics, and on the long end, they’re just long enough for portraits and isolating details. It’s a bonus if the lens can focus closely and has a large enough maximum aperture for photographing in low light.
But getting the level of performance expected these days from a wide-angle zoom lens with a large maximum aperture requires more glass. In turn, the larger elements require a more robust internal structure, making the lens larger, heavier, and more expensive. As businesspeople, we like to keep our costs down. As humans who are already schlepping a lot of bulky gear from job to job, we want a lighter load. While all lenses, especially zooms, are compromises, we still expect uncompromised quality. Inside those parameters—price, mass, and quality—which physical attribute would you be willing to sacrifice to keep the cost and bulk low and the quality high? Aperture or focal length?
I can think of some good reasons to go in either direction, but with its new 28-70mm F2.8 DG DN C lens, Sigma sacrifices a bit of wide-angle focal length to maintain a large aperture. The advantage of a larger maximum aperture is that precise focusing is much easier. By reducing the angle of view on the wide end, the optical path is also more easily corrected with fewer and smaller elements. The optical path is still complex—16 elements, including two each made from low refractive Sigma’s FLD and SLD type glass, and four elements with aspherically curved surfaces in 12 groups—but the lens is well corrected for both distant and close-up photography.
With lenses, savings means little if the image quality is compromised, and compromising on optical or build quality for the sake of price is not what Sigma is building its reputation on. So how does it perform? I tested an E-mount version of the lens on the highest resolution camera available, a 60-megapixel Sony a7R IV.
It’s no surprise that this lens is both sharp and optically well corrected. Although it’s a general-purpose lens, it renders fine details impeccably, even at its closest focusing distance. The nine curved aperture blades make for smooth bokeh. Physics dictates that, as with most lenses, this one is at its sharpest between one and three stops down from wide open, from f/4 to f/8. At typical working distances, sharpness declines from excellent to very good down to f/16, but between f/16 and f/22, diffraction drops acuity precipitously. At the closest focusing distances, this lens is best between f/5.6 and f/11.
Water- and oil-repellant coatings protect the outer surfaces of the front and rear elements. Sigma’s Super Multi-Layer and Nano Porous Coating layers fight internal flare and increase transmission characteristics of the three glass types used in the lens.
Controls on the lens are minimal. The focus and zoom rings are ribbed and easy to grip. The zoom ring is wider and closer to the rear of the lens. An approximately 45-degree twist covers the entire focal length range. Toward the longer focal lengths, an internal barrel extends the lens’ front by roughly an inch. The manual focus ring is at the front end of the outer barrel. Focusing is fast and sure. The only other control on the lens body is a switch for choosing manual or autofocus mode. Missing is the manual aperture setting ring found on other recent Sigma lenses. I miss that feature, as setting the aperture in third-stop increments directly or, alternately, steplessly changing the iris while filming, is advantageous for video work.
Video shooters should be aware that this is not a parfocal zoom. Parfocal zooms hold their focus while changing focal length, and this lens does not. The absence of these features is likely part of the size and weight vs. performance compromise.
In my time with the Sigma 28-70mm f/2.8 DG DN C, what I liked about the lens is that its size and price make it an excellent choice for those looking for a high-quality, general-purpose walk-around lens. For photographers who are solely working as still photographers, it’s a great lens, but it’s not ideal for video.
Atlanta-based commercial photographer Ellis Vener is a contributing editor.