Review by Klaus Schroiff, published June 2012

Kindly provided for testing purposes by Thomas Dres!

A few days ago we had a look at the Sigma AF 105mm f/2.8 EX DG HSM OS macro on a full format Canon EOS DSLR. However, full format cameras remain a niche market - believe it or not but most of the action still happens in the APS-C format segment so let's check how the lens performs here. We've reused some of the text portions where appropriate for obvious reasons.

The predecessor of the Sigma AF 105mm f/2.8 EX DG HSM OS macro was quite successful already and this new version is offering a couple of innovations such as an optical image stabilizer and especially a constant physical length across the focus range. As such it competes with the very comparable Canon EF 100mm f/2.8 USM L IS. It is about 20% cheaper than its mighty rival but it does not feature a weather sealing like the Canon lens.
Used on an APS-C format Canon DSLR the field-of-fiew is equivalent to "168mm" so it's probably too long to be used as a classic portrait lens but there are, of course, many applications beyond the macro scope.

The build quality of the Sigma lens is excellent. It is based on a rubberized metal body with high quality plastic parts based on a metal mount. The focus ring is a bit on the stiff side but does not rotate during focus operations. A focus limiter is implemented in order to avoid focus hunting across the focus range. A barrel-shaped lens hood is also part of the package. Interestingly a "dedicated hood adapter" is also supplied to extend the lens hood for an even more efficient use on APS-C DSLRs. Honestly this feels a bit over the top from our perspective. The optical design includes a floating system to optimize the close focus performance.

The Sigma lens features a virtually silent HSM (Hypersonic Motor) similar to Canon USM (Ultrasonic Motor). AF operations are very fast at conventional distances. This is at least partially achieved by implementing a rather short focus path which makes life a little harder in manual focusing mode. Full-time manual focusing (FTM) is supported. The AF accuracy of the tested sample was good.

As mentioned, the Sigma AF 105mm f/2.8 EX DG OS HSM comes with an optical image stabilizer (OS) with a claimed efficiency of up to 4 f-stops. However, even Sigma admits that the benefits decreases as the shooting distance becomes shorter.

Here's a spec comparison between the Sigma AF 105mm f/2.8 EX DG HSM OS macro and, its direct competitor, the Canon EF 100mm f/2.8 USM L IS macro: