Sigma 28-70mm F2.8 DG DN: What you need to know
Billed by Sigma as ‘a more compact alternative to the existing 24-70mm F2.8 DG DN | Art’, the new 28-70mm F2.8 DG DN is indeed considerably smaller and 365 g (almost a pound) lighter than it’s ‘Art’ series counterpart.
Despite the considerable size and weight (and cost) saving compared to the 24-70mm ‘Art’, Sigma claims that the design of its newest zoom is based on that of the higher-end lens, and should deliver excellent results across its zoom and aperture range.
Click through for a closer look at the new Sigma 28-70mm F2.8 DG DN.
Smaller, lighter and cheaper than 24-70mm F2.8 Art
The new new Sigma 28-70mm F2.8 DG DN weighs in at 470 g (~1 lb) and measures 72 x 102mm (2.8 x 4 inches). That represents a significant size and weight reduction compared to the higher-end 24-70mm, and that meshes with what we’ve learned from speaking to Sigma CEO Kazuto Yamaki over the years: while an extra 4mm on the wide end might not seem like a lot, it’s considerably harder to make a compact, lightweight 24-70mm lens than it is to create a 28-70mm of the same maximum aperture.
The resulting lens handles really nicely. It’s compact without being fiddly, and lightweight without feeling fragile. It balances well on the fairly chunky Panasonic Lumix DC-S1R shown here, and should be a great companion to smaller L-mount and E-mount bodies.
Complex optical design
Clearly this is a very different lens, but despite the difference in focal length range, the optical design of this new zoom is ‘based on’ that of its more costly counterpart in the ‘Art’ line. Optical construction consists of 16 elements in 12 groups (compared to 19 elements in 15 groups for the 24-70mm) and these include three aspherical, two FLD, and two SLD elements. Sigma claims that this design results in ‘thorough correction’ of axial chromatic aberration and coma, but the company recommends that Sony E-mount shooters enable in-camera optical corrections for best results (advice that we’d echo).
As well as plenty of exotic glass, the 28-70mm F2.8 DG DN also features Sigma’s Super Multi-Layer and Nano Porous coatings to keep flare and ghosting low, and contrast high.
Minimum focus changes through the zoom range, from 19cm (7.5″) at the 28mm end, to 38cm (15″) at 70mm. This works out to a useful (but some way off true macro) maximum magnification ratio of 1:4.6 at the long end of the zoom.
Extending zoom and TSC construction
As you can see from this image, the 28-70mm F2.8 DG DN is an extending zoom design, and gets less compact as you zoom in from 24mm.
To keep weight and cost to a minimum, Sigma has made good use of its TSC (Thermally Stable Composite) material in the construction. TSC has comparable thermal expansion qualities to aluminum (which along with glass, is the other primary material used in this lens’s construction). This should improve reliability and optical stability across a wide temperature range.
Weather-sealing (of a sort)
One area where the new 28-70mm F2.8 DG DN is not quite up to par with its Art-series contemporary is weather-sealing. In Sigma’s words, sealing is ‘simple’ and limited solely to a rubber gasket around the lens mount. This helps prevent dust and moisture entering the camera, but how well the lens will stand up to tough weather conditions is an open question. That being said, Sigma has employed a water and oil-repellent coating on the front element.
Filter thread and aperture
The Sigma 28-70mm F2.8 DG DN uses a fairly standard 67mm filter thread, and features nine rounded aperture blades for circular bokeh at wide aperture settings. Bokeh from this lens is generally very pleasant, but we have found that optical vignetting creates uneven bokeh balls towards the edges of the frame at longer focal lengths. You might like the ‘swirly bokeh’ effect that it creates, but you might not.
Automatic and manual focus
Aside from the very nicely-damped focus and zoom rings, there’s only one other physical control on the 28-70mm F2.8 DG DN: a simple AF/MF focus switch. Automatic focus is fast and almost silent, thanks in part to Sigma’s use of a single lightweight focusing element, which keeps the AF unit small. Focus is driven by a stepping motor as we’d expect to see from a lens of this type, and focus breathing is well-controlled (which is useful for video work).
The Sigma 28-70mm F2.8 DG DN will be available in mid-March for $899.
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