An
inexpensive alternative to Nikon's 16mm fisheye.
 |
A
compact lens with a big front element, the Sigma 15mm produces
interesting photographs. Note the lens hood at the left. It
actually consists of two parts: the barrel, which slides over
the lens hood, and a removable cap. Yes, the inside of the
barrel has threads on it, but the angle of view is so wide
you can't leave the barrel on the lens and mount a filter
at the front without severe vignetting. Pity.
| Lens
Formula |
7
elements/6 groups. |
| Filter
Thread |
none
(can use rear gelatin filters) |
| Close
Focus |
5.9
inches (.15m) |
| Angle
of View |
180°
diagonal with 35mm, 120° with D1
|
| Other
Features |
hood built in, infrared marking, depth of field markings,
Autofocus/Manual focus switch |
| Weight |
13.1
ounces (370g) |
| Price |
US$350
(street) |
|
| |
|
The
Basics
The
1.5x change in angle of view with all current Nikon-based digital
SLRs (as of 1/15/03) has led many of us to explore virtually any
and every wide angle alternative available. To wit:
- Very
wide angle lenses. The Sigma and
Nikkor 14mm are the usual choices.
- Accessory
lenses. I wrote about one such low-cost accessory in the 3rd
issue of the D1 Report. In general,
image quality is slightly compromised, but it can be an effective
solution in a pinch. (High quality accessory lenses are available,
but often cost more than the lens you put them on.)
- Relay
lenses.
In my D100, D1, and S2 books I have a section that describes how
to build a relay lens so that the digital angle of view for a
lens is the same as its 35mm angle of view. Of course you lose
automatic features (focus, metering), need several specific pieces
of equipment, lose light, and end up with a gangly mess, but it
works well.
This
review deals with yet another option: the full-frame fisheye.
Full-frame
fisheye lenses (of which there are two, the Nikkor 16mm and the
Sigma 15mm described here) provide a 180 degree angle of view across
the 35mm frame diagonal. These lenses don't attempt to correct for
rectilinear distortion (as do the 14mm lenses) and thus produce
a very unique "look" to a shot. Skateboard and snowboard
photographers in particular seem to love the distorted look these
lenses provide when used very close to a subject. But can they work
for the rest of us who are merely looking for "wider?"
And is 120 degrees across the diagonal wider than we can achieve
otherwise? Read on and find the answers to these questions.
 |
The
Sigma 15mm isn't exactly a lens suitable for architectural
photography, but it can be used for dramatic effect. Used
with care, the viewer probably won't notice anything other
than an extreme perspective. Here, the bottom of the lens
hood is almost touching this statue, and I've tried to keep
straight lines in the shot to a minimum so as not to give
away the linear distortion of the full-frame fisheye. To me,
this adds much more interest to this shot than if I had stepped
back and used a regular wide angle lens.
D100,
ISO 200, -.7 stops fill flash (though I wished I had gotten
the flash up higher). |
This
Sigma has a maximum aperture of f/2.8 and a minimum of f/22. Focusing
can be as close as about half a foot (.15m). Depth of field marks
for f/8, f/11, f/16, and f/22 are provided, as is an infrared focus
index mark. You can't use filters on the front of this lens due
to the built-in "butterfly" style hood, though I've successfully
held Cokin P sized graduated neutral density filters without showing
the edges.
The
focus ring is modest in size, but easily found and, for an autofocus
lens, well damped in feel. There's an auto/manual focus switch on
the lens, but it is quite close to the mount and thus a bit close
to camera on some bodies (the bulges on some Kodak bodies, for example,
make it tough to get to the switch). Focus is obtained in a little
more than a quarter turn from near to far distances. There are 7
elements in 6 groups, so this is a relatively simple lens design.
The
lens comes with a built-in butterfly type hood. You also get a slide-on
lens cap and a padded carrying case for the lens.
The
size is modest: less than 3 inches (70.5mm) in overall length and
nearly the same in diameter. Build quality is quite good overall.
Handling
There's
not much to say. As noted, the focus ring has a decent feel in manual
focus modes, and the lens is well marked for focus decisions.
The
front element is highly convex and it is easy to touch the front
element, even with the built-in hood. The slip-on lens cap is a
two-part piece as it is on all the Sigmas with built-in hoods I've
used. Unlike those earlier ones (Sigma 14mm, Sigma 15-30mm), this
one seems to fit more snugly and is more secure. The pop-off front
cap on the lens cap is essentially useless here, though (on the
15-30mm, you can remove it to mount 82mm filters at longer focal
lengths).
Performance
Focusing
is quick and somewhat quiet. Overall sharpness is excellent, though
I do note a bit of softness in the corners, especially wide open.
Depth of field is phenomenal even wide open, which tends to increase
the perception of sharpness of the lens. Chromatic aberration is
minimal (and not an issue on the digital bodies; a trivial issue
on the 35mm bodies). Light falloff is substantial wide open in the
corners of 35mm shots, only a minor issue for digital. By f/5.6,
light falloff is minimal and ignorable.
Straight
lines that run directly through the center of the frame are rendered
straight, while straight lines near the edges have considerable
barrel distortion (outward curve). On 35mm bodies, the extreme nature
of these curves makes for an interesting (and often useful) effect;
it's so obvious and exaggerated that viewers will know that's what
you were shooting for. On digital bodies, though, this looks less
obvious and can be confused with simply extreme barrel distortion.
Either way, you'll have to spend time learning what does and doesn't
work with this lens (or use a complex after-market software product
such as Panorama Tools to remove the distortion).
 |
 |
| These
images are taken from the exact same tripod position only moments
apart, both with the Sigma 15mm lens. In this image (left),
I've placed the horizon near the bottom edge, which distorts
the straight line and proves the Earth isn't actually round
at all (just kidding). I've underexposed a bit to concentrate
on the sky exposure. There's something interesting in the dynamics
of this image, though I still haven't figured out how much I
like it. I has grown on me, though. |
Alternatively,
here's what happens when you put the horizon in the middle of
the frame (right). The slight upward tilt to the left is actually
correct, that's what the land does--the sea horizon is absolutely
a straight, horizontal line here, though it's hard to see at
this size. Here I've held a graduated neutral density filter
over the sky to allow the foreground to balance better, and
the overall exposure in the sky is about a half stop more than
the one on the left. Note that these are both shot into the
sun at small apertures: no flare! |
Flare
hasn't been a major problem for me, even shooting into the sun.
Indeed, I find that I have more problems with flare on some of my
less wide lenses. Still, it helps to keep indirect light off the
front element of this lens, so I keep my Flarebuster in my kit when
I'm carrying this lens.
Some
may ask how this lens compares to the Nikkor 16mm f/2.8. Despite
the difference in focal lengths, the two lenses appear to have the
same angle of view. The Nikkor is slightly larger, and its built-in
hood isn't as good. The 16mm doesn't focus as close and appears
to still be the same optical design as the original introduced in
1979! The Nikkor is more expensive, but I don't think it delivers
better results. (Admittedly, I no longer have a 16mm to directly
compare against the Sigma 15mm, but my memory of the 16mm makes
me believe that the results I've gotten from the Sigma are slightly
better.) Frankly, I don't know of anything that would make me want
the Nikkor over the Sigma, especially considering the price differential.
Overall,
this strange little lens has found a place in my extended kit. In
a few cases I can simply use it as a very wide angle lens. In others,
I can use the barrel distortion effect to exaggerate something.
-
Optics.
Unstraight lines aren't for everyone, and the inherent barrel
distortion is something that you have to learn how to shoot
with (either you use it for effect, or you frame to minimize
it).
-
Filter
Size. What filter size? Sorry, this lens goes
al fresco.
- Build.
Quite good for the price.
- Focus
Speed. Fast and quiet.
- Optics.
Sharper than I expected.
- Price.
Modest.
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