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Review by Klaus Schroiff and Markus Stamm, published July 2012
The Sigma AF 18-125mm f/3.5-5.6 DC HSM OS is one of the more interesting products in the extreme zoom range league - it tries to keep at least a little rest of sanity with its "mere" 7x zoom ratio. This may look harmless on paper today but it's almost the equivalent to a "28-200mm" on full format cameras - during the film era (not so long ago) this was about as extreme as it got.
The zoom range is just one aspect here though. The Sigma also offers HSM (an ultrasonic AF drive) and, more importantly, OS - Sigma's version of an image stabilizers. Combine all that with an affordable price of around 250 EUR and we seem to have a winner, have we?
In this review we'll have a look at how the lens performs on the Nikon D7000 to find out.
The build quality of the Sigma feels surprisingly good on first contact - that's quite typical for the recent Sigmas actually. The lens body is made of quality materials and there's no significant sign of wobbling despite of the duo-cam design - the two inner lens tubes extend when zooming towards the long end of the zoom range. The broad, rubberized zoom ring operates slightly stiff whereas the focusing feels very smooth.
The tested sample did not suffer from zoom creeping (which may develop over time) but Sigma implemented a transport lock (18mm only) just in case. The front element does not rotate so using an polarizer remains easily possible.
As mentioned the Sigma uses a HSM AF drive. This may sound promising but this incarnation is actually about as noticeable acoustically as a conventional micro motor and it's not really much faster either. Full-time manual focusing is not available, in addition the focus ring rotates during AF operation.
Both the zoom and the focus ring work in "Canon" style, which is the exact opposite of how these rings work on Nikkor lenses. If you're used to the Nikon way of zooming, the Sigma lens may be a challenge for your muscle memory. And if you try to focus manually, you'll have to remember that the focus assist in the viewfinder assumes a Nikon lens and consequently suggest the wrong direction of focus ring movement. However, for most buyers manual focus is certainly not high on the priority list anyway.
Sigma claims a benefit of up to 4 f-stops for its OS (Optical Stabilizer). However, this seems to be a bit optimistic. You may be lucky at times with shutter speeds that slow but it's more realistic to reckon with about 2 f-stops in field conditions.
There's only a single mode OS-switch (on/off). Just like Nikon VR lenses, Sigma's OS on this lens is able to detect panning (object tracking) itself.
Typical for all G type lenses the 18-125 OS does not provide a dedicated aperture ring.
|Equiv. focal length||27-187.5 mm (full format equivalent)|
|Equiv. aperture||f/5.7-f/8.4 (full format equivalent, in terms of depth-of-field)|
|Optical construction||16 elements in 12 groups incl. 1 SLD and 3 aspherical elements|
|Number of aperture blades||7 (rounded)|
|min. focus distance||0.35 m (max. magnification ratio 1:3.8)|
|Dimensions||74 x 88.5 mm|
|Filter size||67 mm (non-rotating)|
|Hood||petal-shaped, bayonet-mount (supplied)|
|Other features||Optical stabilization (OS), silent wave AF drive (HSM)|