Autofocus Sigma 15mm f/2.8 EX Review


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.

Drawbacks

  • 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.

Positives

  • Build. Quite good for the price.
  • Focus Speed. Fast and quiet.
  • Optics. Sharper than I expected.
  • Price. Modest.
 
Quick Evaluation


Recommended; if you need more angle of view and can tolerate the linear distortion, this is a very nice lens.

features
performance
build
value



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