| THE
10-20mm
f/4.0-5.6 EX DC HSM SIGMA
The
Sigma 10-20mm EX HSM lens is designed for use on digital bodies
only. It is in Sigma’s “EX” line, which designates a pro build
quality and distinct finish. In 35mm terms, the lens delivers
a view similar to a 15-30mm lens; very wide, indeed!
-
|
|
10-20mm
f/4.0-5.6 EX DC HSM SIGMA |
BUILD
/ PHYSICAL CHARACTERISTICS
The
Sigma 10-20mm EX lens weighs 470 grams (16.6 oz). Of the four
lenses we tested, it was the second lightest overall. However,
the build quality was very good. The lens has a petal-shaped hood
with a reversible bayonet mount. Unlike some of Sigma’s other
super wide lenses, the 10-20mm lens accepts 77mm front filters.
The
focus ring is farthest away from the body, and the front element
does not turn when focusing. This lens uses Sigma’s Hypersonic
Motor (HSM), so it will autofocus on all Nikon bodies that can
drive AF-S lenses. For digital bodies, this is a non-issue, because
all Nikon digital SLRs can operate AF-S lenses. The manual focus
ring is very smooth, with a very viscous feel. Some may find that
the MF ring feels too slow. Again, if you’re a landscape shooter
using this lens on a tripod, this is a very small nit to pick.
One
difference between the Sigma lens and its Nikkor counterpart is
that the focusing ring turns in the opposite direction. The focusing
scale goes from 0.8 feet (0.24m) to 3 feet (1m) and then infinity.
There are no hyperfocal or infrared markings on the lens. The
zoom ring is very smooth and is marked at 10, 12, 14, 17, and
20mm. Our sample had a standard “side pinch” lens cap which can
be difficult to install or remove with the lens hood in place.
The
Sigma 10-20mm lens has a variable aperture design; f/4.0-5.6.
For people wanting the best low-light focusing performance, the
lack of a constant maximum aperture may be a minor limitation.
However, most landscape photographers will find themselves stopping
down to f/8 or smaller, anyway and using hyperfocal settings.
The lens has a formula of 14 elements in 10 groups. Unlike the
other three lenses tested, the image circle of the Sigma 10-20mm
is too small to cover the entire frame of a 35mm film camera at
any focal length. This is not a major problem if you solely shoot
digital.
PERFORMANCE
The
Sigma 10-20mm lens has two major strong points: sharpness edge
to edge and chromatic aberration. We found that sharpness at 12mm
was very good in the center and did not diminish much at all in
the image edges, even when shot wide-open. When used wide-open
we saw that edge softening began about 240 pixels from the edge
of the frame, but this was a very subtle effect. At 18mm, this
lens was among the sharpest of the four lenses, especially in
the edges. Sharpness at 20mm was on par with its performance at
18mm. As would be expected, maximum sharpness was obtained between
f/8 and f/11, and then diffraction effects began to degrade sharpness
above f/16.
One
tremendous surprise with the Sigma 10-20mm lens was its ability
to handle chromatic aberration (CA). In fact, this lens has almost
no visible CA at f/8 and above at 12mm. At 10mm, there is definitely
some CA in the corners of the image, but it can be easily controlled
during post processing (PP) in Nikon Capture (if you shoot RAW)
or in Photoshop CS2 (RAW or JPEG).
Distortion
was fairly low across the entire zoom range. At 10mm, there was
visible but minor barrel distortion, which became pincushion distortion
above 15mm. This result was not unexpected, considering the incredibly
wide view at 10mm.
The
major weakness of the Sigma 10-20mm lens was in the lens’ light
fall-off characteristics. There was noticeable light fall-off
in the corners of this lens, especially wide-open. While light
fall-off improved above f/8, it was still evident in our images
if you looked carefully enough. This is most likely the result
of the very small image circle produced by this lens. In fact,
the image circle was so small, that there was no focal length
where this lens could be used on a film body without serious vignetting.
Digital users wanting to have a multi-purpose wide-angle lens
that could be used on a film body in a pinch should look elsewhere.
CONCLUSIONS
Overall,
this lens offers outstanding performance at a very reasonable
price (about US $500).
We
think this lens would benefit users who:
•
Hate CA in their images, and don’t have an easy way to correct
it in PP
• Want excellent performance at the wide end
• Want to go wider than 12mm (18mm in 35mm terms)
• Like silent autofocusing
On
the other hand, this lens would be less advantageous to the Nikon
shooter who:
•
Hates light fall-off, or has no easy way to correct for it in
PP
• Wants a constant f/4.0 aperture design
• Uses a 28-70mm lens as their mid-range zoom (leaves a big
gap between 20-28mm)
• Occasionally uses their DX lenses on a film body
|
