Sigma AF 18-125mm f/3.5-5.6 DC - Review / Test Report
Lens Reviews - Canon EOS (APS-C)

Special thanks to Markus Stamm for providing this lens!

Introduction

The Sigma AF 18-125mm f/3.5-5.6 DC is a further representative of the extreme zoom range gang though it´s a little less ambitious with its 7x zoom ratio compared to its 18-200mm brothers and sisters. It is one of Sigma's DC (Digital Camera) lenses featuring a reduced image circle only compatible to APS-C DSLRs. The lens is available for all major APS-C DSLR systems. Within the scope of this review the Canon EOS 350D/Digital Rebel XT was used for testing. The field-of-view of this lens is equivalent to ~29-200mm on full frame cameras.

The optical design is made of 15 elements in 14 groups including 1 SLD (Super Low Dispersion) and 2 aspherical (glass) elements.
The mechanical construction is basically identical to the Sigma AF 18-200mm f/3.5-6.3 DC so please don´t mind that most of the corresponding text is basically a copy here ...

At its 18mm setting the lens is extremely compact at only 70x78mm. As you can see in the product shots above it extends significantly towards the long end of the zoom range and the included lens hood adds a few centimeters more here. The lens uses a so-called duo-cam system with two inner zoom tubes. At just 385g it is also a very light-weight lens. The aperture mechanism features 7 blades. The min. focus distance is 50cm resulting in a max. magnification of 1:5.3 at 200mm. The filter size is 62mm.

As to be expected from a budget lens the mechanical quality can't be stellar but it actually remains surprisingly decent. The broad rubberized zoom ring operates a little stiff and slightly uneven whereas the focus ring feels reasonably smooth. The body A zoom lock switch prevents zoom creeping during transport (only).
Thanks to an IF (internal focusing) design the AF speed is fast (but somewhat noisy). Beyond 50mm AF accuracy is Ok (better than with its 18-200mm sister lens but below it is absolutely dismal (on EOS 350D). The focus ring rotates in AF mode which is a little substandard today. The front element does not rotate so using a polarizer is no problem.




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