The new 28-70 Sigma mirrorless zoom we’ve been expecting turns out to be something we weren’t expecting. Sigma has a decade-long tradition of putting out 24-70 zoom lenses that are a notch below the image quality of its other lenses. So when rumors circulated of a 28-70, it was natural to expect Sigma to address the image quality deficit by doing what Canon did with it’s remarkable RF 28-70 f/2 lens: sacrifice zoom range and size for a higher quality zoom sweet spot. Instead, Sigma used the play gained from the narrower zoom range to shrink the entire lens down to something akin to its well-regarded 18-35mm f/1.8 crop lens.
Lenses are collections of compromises. One variable can often be sacrificed for another, all other things being equal. In this case, Sigma literally kept its earlier 24-70 f/2.8 Art DN lens design, but did add some interesting coatings that might positively affect the contrast. Oddly, this new lens is categorized in Sigma’s C series of lenses, which denotes that it is a high quality lens of the Global Vision line, but not of its top-of-the-line Art series.
The minimum focus distance is about 1/3 macro, making this a very versatile lens. It is coming out in Sony E and L-Mount Alliance L mounts.
Speaking of L-mount, the new form factor works suspiciously well with the Sigma FP body, coming one day prior to the CP + event where some are expecting a revision of that video-oriented body.
With the Sigma-released materials on the lens, they did not include an MTF chart. As this would have provided a rare opportunity to directly compare the effects of different coatings on the same lens design, if anyone locates the MTF chart, please let us know. [Update: we now have copies of the MTF charts for both lenses. They are identical; likely the product of Sigma not reprocessing the MTF chart to take into account the coatings. These will prove an interesting pair to test in the real world for folks like the LensRentals.com crew.]