Sigma AF 18-125mm f/3.5-5.6 DC (Pentax K) - Review / Lab Test Report
Lens Reviews -
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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 length||27-187.5 mm (full format equivalent)|
|Equiv. aperture||f/5.3-f/8.4 (full format equivalent, in terms of depth-of-field)|
|Optical construction||15 elements in 12 groups inc. 1 SLD and 2 aspherical elements|
|Number of aperture blades||7|
|min. focus distance||0.50 m (max. magnification ratio 1:5.3)|
|Dimensions||79 x 83 mm|
|Filter size||62 mm (non-rotating)|
|Hood||petal shaped (supplied)|