Sigma AF 18-200mm f/3.5-6.3 DC - Review / Lab Test Report
Lens Reviews - Canon EOS (APS-C)
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Review by Klaus Schroiff, published December 2005

Special thanks to Jochen Pölke for providing this lens!


Sometimes we are joking about a hypothetical 18-300mm f/1.8 to meet all our photographic needs. Well, we aren't quite there yet nor will we ever see such a lens on a DSLR but the manufacturers are at least scratching this focal length range with some 18-200mm variants and the Sigma AF 18-200mm f/3.5-6.3 DC is one of the representatives here. It is one of Sigma's DC (Digital Camera) lenses with a reduced image circle only compatible to APS-C DSLRs. The lens is available for all major APS-C DSLR systems. The field-of-view of this lens is equivalent to ~29-320mm on full frame cameras.

An extreme 11x zoom lens like the Sigma has to come up with a complex optical design in order to deliver an acceptable quality - it is made of 15 elements in 13 groups including 2 SLD (Super Low Dispersion) and 2 hybrid aspherical elements.
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 405g it is also a very light-weight lens. The aperture mechanism features 7 blades. The min. focus distance is 45cm resulting in a max. magnification of 1:4.4 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 features a crinkle finish similar to Sigma EX used in Sigma's pro grade lenses without reaching the solid feel naturally. A zoom lock switch prevents zoom creeping during transport.
Thanks to an IF (internal focusing) design the AF speed is reasonably fast. However, in the field the Canon EOS 350D didn't quite like the lens despite good lighting conditions. The AF hunted frequently often without finding a correct focus point especially towards the long end of the zoom range where the AF is actually used out-of-specs ("certified" till max. f/5.6 on the EOS 350D). Consequently the viewfinder image is also very dark at 200mm. The focus ring rotates in AF mode which is a little substandard today. The front element does not rotate so using a polarizer is, in principal, no problem (but not recommended due to even more pronounced AF problems).