ver many years Sigma struggled to take off in the fast standard zoom arena for APS-C DSLRs. That segment had been dominated by the Tamron AF 17-50mm f/2.8 (VC) with its highly attractive price/performance ratio and the all mighty but expensive OEM offerings (Nikon AF-S DX 17-55/2.8 and Canon EF-S 17-55/2.8 IS) owning the quality crown. However, with the release of the AF 17-50mm f/2.8 EX DC HSM OS in 2010, Sigma finally offers a lens that is able to compete in this arena.
That alone may not be all THAT exciting - we've seen many fast standard zoom lenses by Sigma come and go - but this one is a bit more special. Within the recent years, Sigma announced a couple of lenses featuring their new FLD glass and the new 17-50mm f/2.8 OS is among them. FLD glass has an optical characteristic similar to fluorite glass. Such glass elements can be used to compensate optical aberrations (defects) more efficiently than conventional "special" elements such as Sigma's more commonly used SLD glass. We were already very impressed by the performance of the Sigma AF 8-16mm f/4.5-5.6 DC HSM which also benefits from FLD elements so there's some well founded hope that the AF 17-50mm f/2.8 EX DC HSM OS stands out from the ordinary as well.
So, let's have a look at how the lens performs on our current DX test camera, the Nikon D7000.
Via Philippe Gassmann