Review by Klaus Schroiff, published January 2014

Introduction

The build quality of the Sigma lens is - although it may still be surprising for some - simply superb. Besides some metal parts, Sigma uses a new material called TSC (Thermally Stable Composite) which contributes to the high quality perception. There's no wobbling whatsoever and that's despite a duo-cam zooming mechanism (two inner lens tubes). The broad zoom and focus rings are nicely rubberized and operated smoothly. It is worth to mention that the lens is rather massive especially when zooming towards the 105mm setting and with attached lens hood.

The 24-105mm f/4 HSM DG OS | A features Sigma's ultrasonic AF drive (HSM="Hypersonic") which is similar to Canon's USM both in terms of high speed and negligible noise. Of course, this applies to phase detection AF whereas in Live View mode you shouldn't expect wonders here. Image stabilizers are mainstream theses days and Sigma has implemented their variant (OS="Optical Image Stabilizer") which provides an equivalent gain of around 3 f-stops in real life situations. It is also worth to note that the lens is compatible to Sigma's USB dock (for AF/OS tuning) and they also offer a mount conversion service (e.g. Canon EF to Nikon).

Here’s how the specs compare against its primary competitor: