Sigma AF 18-125mm f/3.5-5.6 DC (Pentax K) - Review / Lab Test Report
Lens Reviews - Pentax
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Review by Klaus Schroiff, published May 2007

Special thanks to Rüdiger Neumann for providing this lens for testing!


The Sigma AF 18-125mm f/3.5-5.6 DC is one of the available extreme range zoom although it´s a little less ambitious compared to its 18-200mm/18-250mm brothers and sisters. It is one of Sigma's DC (Digital Camera) lenses with a reduced image circle optimized for today's DSLRs. The field-of-view of this lens is equivalent to ~27-188mm on classic full format SLRs.

The Sigma is an extremely compact lens at its 18mm setting - just 70x78mm. However, as you can see in the product images below above it extends significantly towards the long end of the zoom range and the included lens hood adds a few centimeters more. The lens uses a so-called duo-cam system with two inner zoom tubes to achieve this. As to be expected from a budget lens the mechanical quality can't be stellar but it remains actually surprisingly decent with no significant wobbling. The broad rubberized zoom ring operates a little stiff and slightly uneven whereas the focus ring feels reasonably smooth. Sigma implemented a zoom lock switch to prevent zoom creeping during transport (at 18mm only).

The lens has no internal AF motor and relies on a slotted drive screw operated by the camera. The AF speed and accuracy is generally fine although the AF struggles quite a bit in low light.

Equiv. focal length27-187.5 mm (full format equivalent)
Equiv. aperturef/5.3-f/8.4 (full format equivalent, in terms of depth-of-field)
Optical construction15 elements in 12 groups inc. 1 SLD and 2 aspherical elements
Number of aperture blades7
min. focus distance0.50 m (max. magnification ratio 1:5.3)
Dimensions79 x 83 mm
Weight385 g
Filter size62 mm (non-rotating)
Hoodpetal shaped (supplied)
Other features-

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