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Sigma AF 18-200mm f/3.5-6.3 DC - Review / Lab Test Report |
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Lens Reviews -
Canon EOS (APS-C)
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Page 1 of 2
Review by Klaus Schroiff, published December 2005
Special thanks to Jochen Pölke for providing this lens!
Introduction
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).
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