Sigma AF 14mm f/2.8 EX Aspherical HSM

This Sigma 14mm lens came in handy whenever my 20mm was too long to include all important areas of a subject or scene. Extremely short focal lengths are often useful problem-solving tools. (Nikon N90s; Bogen tripod; f/22; Ektachrome E100VS.)
Photos © 1999, Peter K. Burian, All Rights Reserved

Until recently, most photographers considered a 19mm or 20mm focal length as the ultimate in ultra-wide, but this is rapidly changing. Thanks to the new technologies for making more affordable aspherical elements, much shorter lenses are becoming readily available. The first independent brand manufacturer to release a 14mm lens of this type, Sigma incorporated a bonus in their model: an ultrasonic focus motor. More importantly perhaps, they offer premium-grade optics for excellent image quality as I discovered during my tests while shooting stock in San Diego and Toronto.

Primary Features. Do note that the Sigma AF 14mm f/2.8 EX Aspherical HSM is not a fisheye, but a true rectilinear lens. Barrel distortion is well corrected, so straight lines even at the edges of the frame are accurately rendered. Before moving on to consider optical performance in more detail however, let's review the technical details of this lens, as follows.

· It incorporates the fast/silent Hypersonic Focusing system, described later, in models intended for Canon, Nikon (D), and Sigma autofocus SLRs. Nikon owners should note that AF operates only with the more recent cameras: F5, F100, N90 series, N70, N60, and the Pronea series. Manual focus is possible even in the AF mode. After the lens stops autofocusing, you can touch up focus by turning the ring, while maintaining slight pressure on the camera's shutter release button.

· Models designed for Minolta and Pentax cameras incorporate a conventional focus motor. These do require you to switch to MF for any manual focus operation.

· The maximum aperture of f/2.8 is very wide, making this lens useful for photojournalism in low-light situations. I was able to get sharp pictures handheld inside Spanish missions at 1/15 sec (and even longer with my elbows braced), important because flash is not practical with such short focal lengths. That's because very few flash units (even with accessories) can cover the 114° field of view, making such lenses more likely to be used with available light only.

· As hinted earlier, the optical formula includes aspherical--with a non-spherical surface--elements to correct aberrations. This type causes all light rays to converge on a common plane. Such elements offer several benefits: they correct linear distortion and spherical aberration (curvature of field) for more consistent edge to edge sharpness even at wide apertures; reduce halo and comatic flare; and minimize size/weight as fewer elements are required.

· In order to reduce the risk of flare (from light striking the front element) Sigma has included a built-in "notched" lens hood: cut out at the corners to prevent vignetting of the image area. In order to mount a lens cap, you do need to add an adapter ring because the cap will not fit over the bulging optics without one. This is common in other brands of super wide lenses, too. But remember to remove this circular adapter before taking any pictures. If you fail to do so, all of your photos will have severe darkening of all corners.

· Because filters cannot be mounted on the front of 14mm lenses, there is a built-in gelatin filter holder at the rear. Simply cut the right size using the "guide plate" accessory and insert the small filter in the slot provided behind the rear optical element. (Gelatin filters are available from professional photo retailers.)

· Mechanically and cosmetically, this is clearly a high grade lens, as suggested by the EX designation, used only for Sigma's latest pro-caliber lenses. The barrel is made of aluminum alloy, the mount is stainless steel, and the matte-black ZEN finish offers a professional look plus scratch-resistance. You'll find a distance scale (feet and meters) under glass as well as a depth of field scale. Models intended for some brands of cameras include an AF/MF switch and an aperture ring for setting f/stops with detents at full stops.

· The wide, rubberized manual focus ring is well damped, with plenty of friction for a familiar "feel."

· The close-focusing ability is highly desirable for maximizing depth of field, when shooting at the smallest apertures, as discussed later.

I found the Sigma 14mm lens ideal whenever I wanted to include a great deal of the environment to ensure a sense of place in travel photography. (Nikon N90s; f/5.6; Fujichrome Velvia.)

Optical Evaluation. Considering the incredibly wide field of view, a 14mm lens is not exactly an all-purpose piece of equipment, but it came in handy for photographing the expansive Mission San Luis Rey, the museums of Balboa Park, and the extravagantly beautiful grounds and buildings of the Hotel Del Coronado across the bridge from San Diego. It would also be a great choice for grand landscapes or in cramped interiors where you want to include as much of the subject as possible, without switching to a fisheye lens.

When reviewing my slides under a 10x loupe on a light table, I made the following notes:
· Linear distortion is indeed extremely well corrected. As long as I held the camera perfectly level--with the film plane parallel to the subject--all lines were rendered as straight and true. As with any ultra-wide lens, there is some limited barrel distortion, but this is surprisingly well controlled. As with any wide angle lens, tilting the camera upward produces unusual effects, highly useful in interpretive (non-documentary) photography.

· Light falloff is minimal even at wide apertures and completely gone by f/5.6. Since most of my outdoor work was at f/16, there is absolutely no darkening of the corners of my images in the vast majority of the slides.

When using the Sigma 14mm lens, I often took advantage of its characteristics for interpretive images, instead of shooting documentary records of architecture. Note the very high sharpness and definition of intricate detail across the entire frame. (Nikon N90s; f/16; Fujichrome Velvia.)

· At every aperture from f/5.6-f/16, this lens produced images suitable for excellent 16x24 prints with high edge to edge sharpness. The slides also exhibit very good contrast, great clarity, and impressive definition of intricate detail. Even at the widest and smallest apertures, image quality is adequate for beautiful 11x14 prints or double page spreads in magazines or books.
Effective Techniques. Making successful images with a 14mm lens does take some practice, considering the unusual characteristics of such optics. Consider the following to maximize the visual impact and technical quality of your photographs.

· Unless you tilt the lens upward, you'll get a vast amount of empty space in the foreground when photographing buildings. Move in close when possible or exaggerate the "leaning over backward" effect so the viewer is clearly aware of your intentions.

· The expanded spatial perspective is far more noticeable than with a 20mm lens, creating great apparent distortion of the relative size of objects within a scene. Nearby objects become unusually prominent, overpowering the scene, at an apparent size far beyond the norm. Meanwhile, anything at a greater distance is "pushed back," rendered much smaller than the eye perceives and receding into the distance. Take advantage of this characteristic, including subject matter in the immediate foreground, the mid-ground, and the background for a sense of depth, or a three-dimensional "feel" in a two-dimensional photograph.

· Exploit the benefits of expanded depth of field as well, to render all subjects from foreground to infinity within the zone of apparent sharp focus. A hillside of wildflowers, for instance--with an expansive sweep of blossoms as far as the eye can see--makes for an appealing picture. Set focus for the hyperfocal distance to maximize depth of field at any aperture. At f/8 focus at 3.2'; at f/11 focus to 2.4'; at f/16 focus to 1.2'; and at f/22 focus at 1.2'. Use these recommendations, and virtually everything in the photograph will appear sharply rendered. (The depth of field extends from one-half the focused distance to infinity with this technique.)

· Compose carefully. The extremely wide angle of view can include numerous subject elements that will compete for viewer attention. Strive to create images with a clear message or sense of purpose. Move in closer to eliminate extraneous details.

· Flare is well controlled, but take care in backlighting, as with any 14mm lens. Because the optics protrude and the hood can provide only minimal shading, avoid situations where the sun is in the frame. Try to shade the lens with your hand, the branch of a tree, or with a Flare Buster, an adjustable accessory that can be positioned exactly where required (from Gran View Inc., (888) 993-5273 or www.granview.com)

· Compensate for underexposure, which is likely with any super wide lens where a lot of bright sky, water, sand, or snow is included in the frame. As a starting point, dial in a +1 stop compensation factor in Automatic, or open up in Manual mode, and bracket exposures if using slide film.

Conclusion. Aside from its problem-solving abilities, a 14mm lens should be considered for creating special effects impossible with longer focal lengths. Some of your pictures will seem "distorted" but others will be "dynamic" or "dramatic." If you want to expand your horizons and are willing to experiment, this Sigma lens can open new doors to creativity. Though not inexpensive, it is relatively affordable for the focal length and will reward the investment with professional-caliber image quality.

With an angle of view of 114°, it can be difficult to compose without including a vast expanse of foreground in architectural photography. A slight upward tilt can help, at the risk of some linear distortion. (Nikon N90s; Bogen tripod; f/16; Ektachrome E100SW.)

Hypersonic Focusing

Sigma now offers the Hypersonic focus technology in several lenses, including this 14mm f/2.8 EX Aspherical HSM model, in Canon, Nikon (D), and Sigma AF mount. The ultrasonic motor employs vibrational energy unlike conventional DC motors which convert electromagnetic force into rotational force. In HSM motors, friction between a stator and a rotor creates oscillation energy ("flexural progressive wave") to generate rotational force. Several benefits are claimed: nearly silent operation, better starting/stopping response, longer motor life, and the ability to override AF without switching over to Manual focus.

Is AF necessary with a 14mm lens where depth of field is so extensive as to mask any manual focusing error? In my opinion it is, if you want precise focus on the primary subject area in serious photography. This is more easily accomplished with autofocus than by eye, with ultra-wide lenses. Aside from architecture and cityscapes, I also tested the Hypersonic system with skaters on an outdoor ice rink, both approaching and pulling away from my position, in continuous/predictive follow focus. The camera used for my tests was a Nikon N90s. I made the following assessments:
· Autofocus was precise and highly accurate with stationary subjects such as the incredible architecture of Balboa Park.

· Because of the wide f/2.8 maximum aperture, focus acquisition was excellent even in low light. (The wide aperture transmits plenty of light to the AF sensors assuring quicker focus acquisition.)

· When tracking skaters, all frames in series of six were razor sharp. Continuous autofocus performance was excellent even with erratic motion.

· In summary, the Sigma Hypersonic focusing system is indeed very successful. It will meet the expectations of most serious photographers.
Note: The parts and technology employed in the Sigma Hypersonic system are not the same as in Canon's Ultrasonic system. In fact, HSM contains many components exclusive to Sigma.

Technical Specifications

Lens Construction: 14 elements in 10 groups
Angle Of View: 114.2°
Maximum/Minimum Aperture: f/2.8 and f/22
Minimum Focusing Distance: 7.1" (0.18 meters)
Maximum Magnification: 1:5.2
Filter Size: N/A; rear mounted gel only
Lens Hood: Built-in
Dimensions: 3.15x3.6" (80x91mm)
Weight: 23.1 oz (655g)
Available Mounts: Sigma AF (HSM), Canon EF (HSM), Nikon AF/D (HSM); Pentax AF and Minolta AF (conventional focus motor)

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