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Get Into Superwide With Sigmas 20mm f1.8 EX DG Aspherical RF Lens
By George Schaub • September, 2001
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When you focus close and stop down (here, to f/16) the
20mm focal length gives you an incredible depth of field
and a great sense of place, due to the seeming falloff
of the background from the foreground subject. This and
other shots here were made with a Canon EOS 1N at the
Dixie Crossroads Garden in Titusville, Florida. Exposure
on Kodak Ektachrome VS 100 was f/16 at 1/30 sec, handheld.
Photos © 2001, George Schaub, All Rights Reserved
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Photographers have always
been fascinated by super wide angle focal lengths. This focal length
range, including 20mm, expands peripheral vision beyond the scope of
human vision, and does so with a potential depth of field that makes
for an often-surreal sense of place. Look up and the superwide makes
the sky soar; bend backward and any sky looks like it’s in Montana.
True, there is inevitable bending of lines that are off the X/Y axis,
but this only adds to the visual fun. Some believe that superwides alter
perspective too much, but in truth no lens changes the actual relationship
of subjects near to far. Crop a 20mm lens to a 50mm angle of coverage
and shoot from the same camera-to-subject distance and you’ll
see that it’s true. But the superwide offers more to see when
shooting both vertically and horizontally, thus we seem to get spatial
distortion. One big bonus with superwides is that they generally allow
for much closer minimum focusing distances; coupled with their incredible
potential depth of field we get images from superwides unlike those
from any other lens.
Near all-encompassing, the
near 95° angle of view of the new Sigma lens makes it the perfect focal
length for candid street photography, opening up and expanding narrow
spaces, and even for certain types of landscape work where the composition
holds defining foreground subjects set against a receding background
context. It is also an ideal lens for digital SLRs, as the loss of coverage
due to a smaller capture frame forces the use of a superwide on a digital
SLR to get moderate wide angle coverage.
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You can always play with edges with a 20mm, as was done
here by tilting the camera down when photographing these
colorful posts. Note the edge sharpness and color richness,
due partly to Kodak Ektachrome 100 VS film but also in no
small part to the optical quality of the Sigma lens.
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The Sigma 20mm f/1.8 EX DG
Aspherical RF is one of several Sigma lenses in this class, which includes
the 8mm f/4 fisheye, the 14mm f/2.8, the 15mm f/2.8, and their 24mm f/1.8
and 24mm f/2.8 lenses. Some might argue that the 24mm focal length is
too long for superwide status, but we threw this focal length in for those
who like a superwide view with a bit less of a surreal touch. Sigma claims
that this is the first 20mm superwide lens with a large aperture of f/1.8
and angle of view of 94.5°. To expand the usefulness of the lens Sigma
has made it with macro focusing capability with a minimum focusing distance
of 20cm/7.9" (reproduction ratio 1:4). In addition, the iris diaphragm
has nine diaphragm blades to obtain a more natural looking out of focus
image, although this reviewer tends to work with middle to narrow apertures
to get a deep zone of sharpness with this focal length lens type.
The Sigma 20mm f/1.8 incorporates
an aspherical lens element in the front as well as rear lens groups, to
minimize distortion, spherical aberration, and astigmatism. The lens has
non-vignetting optical construction in order to obtain adequate peripheral
brightness with open aperture, an approach that makes it ideal for both
film and digital SLR cameras. Corner vignetting, the bane of some superwides,
seems to have been greatly reduced with this Sigma entry.
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The Sigma’s maximum aperture of f/1.8 allows you to isolate
foreground subjects with a very shallow depth of field.
Exposure was f/1.8 at 1/500 sec. |
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The lens also incorporates
a rear focus system eliminating front lens rotation, thus allowing the
use of a Perfect Hood and easy use of polarizing filters. The lens also
incorporates a dual-focus mechanism--the focusing ring does not rotate
during autofocus, yet it provides adequate focusing torque of the focusing
ring during manual focusing operation.
The 20mm f/1.8 makes switching
from autofocus to manual focus easy. The push/pull device clicks the lens
instantly from one to the other, without the need to stop shooting and
flip a switch. Yet autofocus with a superwide is often a bit odd, as the
image always seems in focus except when moving the view from quite near
to far. That’s why use of a depth of field preview function is so important
with this type of lens. When working at narrow apertures it can be hard
to distinguish what’s in or out of focus without it. With a minimum aperture
of f/22 the Sigma can really deliver some startling close-up/ distance
zone of sharpness images. And at the maximum aperture of f/1.8 you can
shoot both in low light with slow speed film and get some great background
unsharpness effects. For our field tests we brought the Sigma f/1.8 20mm
lens to a carnival and to a funky sculpture garden right here in world
headquarters’ area--at the Dixie Crossroads Restaurant. Besides from having
perhaps the best coconut shrimp anywhere, Dixie Crossroads offers a true
roadside America diversion while awaiting the call to your table.
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Images made with the Sigma lens were tack sharp, and all
the EOS 1N functions operated flawlessly with the lens.
This exposure was made on Aperture Priority Exposure mode
set at f/11 with a -2/3 exposure compensation. Autofocus
was quick and virtually noiseless. |
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The first thing that strikes
you about the Sigma is its smooth, easy focusing, one that snaps to whenever
you touch the shutter speed dial. If you need to switch to manual there’s
a quick, one-touch step that can be easily done without the need to remove
your eye from the finder. Although the lens has some heft (at 18.3 oz)
it handled and balanced well. The impressive glass measures only about
3.4" so it doesn’t intrude much on camera bag space, at least when you
consider that fast maximum aperture.
Photographs were made at the
extremes and middle of the aperture range, and louping images at every
step showed this to be super-sharp contender. We used the lens on a Canon
EOS 1N, but it’s also available for Sigma SA, Minolta D, Nikon D, and
Pentax mounts as well.
Is a 20mm superwide, and specifically
the Sigma f/1.8 version, for you? It’s hard not to get into working with
this specialty focal length. As with any such lens, it can’t but help
open your eyes to new composition and imaging possibilities.
For more information, contact
Sigma Corporation at (631) 585-1144; fax: (631) 585-1895; www.sigmaphoto.com
Technical Specifications
Aperture Range: f/1.8-f/22
Construction: 13 elements, 11 groups
Focusing System: Rear focusing
Angle Of View: 94.5mm
Minimum Focusing Distance: 7.9" (reproduction ratio 1:4)
Filter Size: 82mm
Size: 3.5", diameter, 3.4", length
Weight: 18.3 oz
Mounts: Sigma SA, Minolta D, Nikon D, Pentax, and Canon
MSRP: $689
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