When Sigma came out with its 28-70 f/2.8 lens for mirrorless cameras, it was a show of the power of coatings – taking the existing 24-70’s lens design and employing different coatings and a shorter zoom range to produce something smaller and – according to the MTF chart – superior.
But then Sigma revealed another industry innovation: it recognized early that the first copies of the lens were showing reduced anti-ghosting abilities, a problem often corrected with coatings. Something was goofy, and before they even had a fix, they publicly announced they had a problem and stopped production.
These lenses are now being replaced for free. The time between launch and problem discovery was about two weeks, and it took only 6 weeks from launch for a fix to be put in place and a process for early lenses to be replaced. Sigma may be trying to bring some cutting edge coatings tech to the lens industry, but its service innovations will likely be remembered more than slight contrast improvements through the elimination of ghosts.