As their name suggests, ultra-wide-angle lenses take in very wide angles of view. This lets you produce dramatic landscape vistas in a single shot or move in very close to a subject and still show its environment. In this issue of OP, we have an article on the creative use of the close-up wide-angle technique. It's one of the most powerful effects in landscape photography, and it's ideally suited to these lenses (see "Close-Up Wide-Angle").
Canon EF 16-35mm ƒ/2.8L II USM, Nikon AF-S Zoom-Nikkor 14-24mm ƒ/2.8G ED
Whether or not a lens is ultra-wide-angle depends on the format of the camera on which it's used. For our purposes here, we consider a lens providing an angle of view of 99° or greater to be ultrawide. This means a focal length of 18mm or shorter for a 35mm SLR or "full-frame" DSLR, a focal length of 12mm or shorter for an APS-C DSLR and a focal length of 9mm or shorter for a Four Thirds System or Micro Four Thirds System camera. Thus, an ultra-wide-angle zoom is one with a wide-end focal length in this range. The accompanying chart presents a sampling of what's available for these camera formats.
The advantage of an ultrawide zoom over a prime super-wide-angle lens is compositional flexibility: You can change the amount of background area that appears around a nearby subject by zooming the lens. You also can adjust the framing of a distant scene without moving the camera just by zooming the lens. Note that changing the framing by zooming the lens doesn't change the perspective; you must move the camera to do that.
Ultrawide Lens Considerations
Lenses work by refracting light rays. Really wide-angle lenses have to bend light rays to a greater degree than longer-focal-length lenses do. This makes ultrawide lenses more susceptible to various aberrations and distortions. And zoom lenses change the way they bend the light as they change their focal lengths, compounding the problems. It's not an easy task to design and produce a good super-wide-angle lens, especially a super-wide zoom.
Canon EF-S 10-22mm ƒ/3.5-4.5 USM, Pentax DA 12-24mm ƒ/4.0 ED AL (IF), Nikon AF-S DX Zoom-Nikkor 10-24mm ƒ/3.5-4.5G
Distortion. Theoretically, a nonfisheye lens should render a straight line as a straight line, no matter where it falls in the image frame. In practice, long lenses tend to bow straight lines near the edges of the frame inward (pincushion distortion), and short lenses tend to bow them outward (barrel distortion). A zoom lens might exhibit both types of distortion, the type and degree varying with the selected focal length. Lens designers use various combinations of elements to counter distortion, aspherical elements being especially useful for this. But you'll still find some barrel distortion in ultrawide zooms, especially at their shortest focal lengths. If you want to avoid this distortion—and it can be used to creative effect at times—the best way to deal with it is to compose so there are no straight lines near the frame edges.
Note that the tilting inward of vertical subjects near the frame edges when the camera is tilted up and the expanded perspective that occurs when using a wide-angle at close range aren't optical distortions. They're natural effects of perspective. To avoid the appearance of tilting, you need to have the DSLR's sensor parallel to the subject. In many cases, this requires a tilt-shift lens.
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Ultra-wide-angle lenses are prone to barrel distortion, an aberration where straight lines appear to bend outward. Many software programs include lens correction for adjustments.
Aberrations. Fast wide-angles are especially prone to spherical aberration due to the fact that light rays traveling through the edges of the lens don't focus at the same plane as rays traveling through the lens closer to its center. Again, aspherical elements can correct this to a large degree. Stopping the lens down also helps.
There also are chromatic aberrations, which cause different wavelengths of light to focus at different distances from the lens. Extra-low-dispersion elements are used to correct this. These have designations like ED (Nikon), UD and SUD (Canon), FLD (Sigma), SD (Tokina), LD (Tamron) and Super ED (Olympus). Like aspherical elements, these are found in the higher-end ultra-wide-angle zoom lenses.
Vignetting. The image produced by a lens tends to be brightest at the center, where the light rays travel straight through, and dimmer at the edges of the frame, where the light rays are bent the most. This darkening of the corners and edges of the image is vignetting, and it's especially apparent in wider-angle lenses. Most ultrawide zooms are corrected for vignetting, but it's not possible with current technology to completely eliminate it. You can reduce vignetting by stopping the lens down.
Tamron SP 10-24mm F/3.5-4.5 Di II LD Aspherical, Olympus Zuiko ED Digital 7-14mm ƒ/4.0, Tokina DX 11-16mm ƒ/2.8 PRO DX
There are software solutions to lens problems like distortion, vignetting and even chromatic aberration, as well. DxO Optics Pro and Adobe Photoshop and Lightroom provide such capabilities. Nikon Capture NX 2 software can correct distortion in many images as long as a Nikon DSLR and Nikon D- or G-type lens was used to shoot the picture.
Focus Shift. A true zoom lens maintains focus as you zoom it. Most zooms on the market change focus as they're zoomed, however. This isn't a problem when using autofocus because the AF system automatically corrects for it. But when you're focusing manually, you need to be careful as you zoom. If you zoom the lens to change the framing, be sure to refocus at the new focal length.
Aperture Range. Constant-aperture zoom lenses maintain the aperture as they're zoomed, but they tend to be expensive. In variable-aperture zooms, the maximum aperture size shifts as the focal length is increased. TTL metering automatically compensates for this, but you need to pay attention if you're shooting with a fast aperture to keep the background out of focus.
Sigma 8-16mm ƒ/4.5-5.6 DC HSM
How do you know which type your zoom is? Look at its designation. A 16-35mm ƒ/2.8 lens provides a maximum aperture of ƒ/2.8 at all focal lengths, and will remain at the set aperture as you zoom it. A 12-24mm ƒ/4-5.6 zoom has a maximum aperture of ƒ/4 at 12mm, which decreases to ƒ/5.6 at 24mm; the set aperture will decrease as you zoom the lens from wide focal length to long.
Depth Of Field. Depth of field refers to the distance in front of and beyond the point of focus in which objects in a scene appear acceptably sharp in the image. It depends on a number of things, including the viewed image size, viewing distance, camera format, lens focal length, focused distance and aperture.
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|FULL FRAME ULTRA-WIDE ZOOMS**||Elem./
|Canon EF 16-35mm ƒ/2.8L II USM||16/12||10.9 in.||108||3||2 UD||22.6 oz.||$1,699|
|Canon EF 17-40mm ƒ/4L USM||12/9||10.9 in.||104||3||1 SUD||17.6 oz.||$799|
|Nikon AF-S Zoom-NIKKOR 14-24mm ƒ/2.8G ED||14/11||10.9 in.||114||3||2 ED||34.2 oz.||$1,799|
|Nikon AF-S Zoom-NIKKOR 16-35mm ƒ/4G ED VR||17/12||11 in.||107||3||2 ED||24.0 oz.||$1.159|
|Nikon AF-S Zoom-NIKKOR 17-35mm ƒ/2.8D IF-ED||13/10||10.9 in.||104||3||2 ED||26.3 oz.||$1,769|
|Sigma 12-24mm ƒ/4-5.6 DG HSM II||17/13||11 in.||122||4||5 (4 FLD)||23.6 oz.||$959|
|Sony/Zeiss 16-35mm ƒ/2.8||17/13||12 in.||107||3||2 (1 SED)||30.3 oz.||$1,899|
|Tokina 16-28mm ƒ/2.8 PRO DX||15/13||11 in.||107||3||3 SD||33.5 oz.||$859|
|APS-C ULTRAWIDE ZOOMS***|
|Canon EF-S 10-22mm ƒ/3.5-4.5 USM||13/10||9.5 in.||107||3||1 SUD||13.6 oz.||$839|
|Nikon AF-S DX Zoom-NIKKOR 10-24mm ƒ/3.5-4.5G||14/9||7.3 in.||109||3||2 ED||16.2 oz.||$899|
|Nikon AF-S DX Zoom-NIKKOR 12-24mm ƒ/4G IF-ED||11/7||11.8 in.||99||3||2 ED||16.4 oz.||$1,225|
|Pentax DA 12-24mm ƒ/4 ED AL (IF)||13/11||12.0 in.||99||2||Yes||15.2 oz.||$699|
|Sigma 8-16mm ƒ/4.5-5.6 DC HSM||15/11||9.4 in.||114||3||4 FLD||19.6 oz.||$699|
|Sigma 10-20mm ƒ/3.5 EX DC HSM||13/10||9.4 in||102||4||3 (2 SLD)||18.3 oz.||$649|
|Sigma 10-20mm ƒ/4-5.6 EX DC HSM||14/10||9.4 in||102||3||3||16.4 oz.||$489|
|Sony DT 11-18mm ƒ/4.5-5.6||15/12||9.6 in.||104||Yes||Yes||12.7 oz.||$699|
|Tamron SP 10-24mm F/3.5-4.5 Di II LD Aspherical||12/9||9.4 in||108||6||2 LD||14.3 oz.||$499|
|Tokina AT-X 116 PRO DX 11-16mm ƒ/2.8||13/11||11.8 in.||104||2||2 SD||19.7 oz.||$659|
|Tokina AT-X 124 PRO DX II 12-24mm ƒ/4||13/11||11.8 in.||99||2||1 SD||19.0 oz.||$549|
|FOUR THIRDS SYSTEM ULTRAWIDE ZOOMS|
|Olympus Zuiko Digital 7-14mm ƒ/4.0 ED||19/12||9.8 in.||114||2||2 (1 SED)||27.5 oz.||$1,569|
|Olympus Zuiko Digital 9-18mm ƒ/4.0-5.6 ED||13/7||9.8 in.||100||2||1 ED||9.7 oz.||$519|
|Panasonic Lumix G Vario 7-14mm ƒ/4.0 ASPH HD||16/12||9.8 in.||114||2||4 ED||10.6 oz.||TBA|
|* Maximum angle of view for format (full frame for full-frame lenses, APS-C for APS-C lenses, 4/3rds for 4/3rds lenses).
** Full-frame ultra-wide-angle lenses can be used on compatible-mount APS-C cameras, too, but won't produce ultrawide angles of view due to the smaller image sensor's crop factor.
*** APS-C-format Canon lenses can't be mounted on larger-format Canon DSLRs; APS-C-format Nikon lenses can be used with full-frame Nikon DSLRs, but the camera will crop the image to DX format; APS-C-format Sony lenses can be mounted on full-frame Sony DSLRs, but will vignette; APS-C-format Sigma, Tamron and Tokina lenses are for APS-C-format DSLRs only; all Pentax DSLRs (except the new 645 medium-format and Q compact model) are APS-C.
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Because they have to bend light from such extreme angles, ultra-wide-angle zooms are complex devices with a lot of elements. Also, exotic specialty glass, like the Sigma FLD element here, is often used to maintain sharpness and minimize aberrations.
Standard depth-of-field tables and the depth-of-field scales on the few lenses that have them are based on a certain-sized circle of confusion, which, in turn, is based on the eye's ability to detect unsharpness in a given-sized print at a given viewing distance. If you produce a bigger print, or view it at a closer distance than this standard or view the image at 100% on-screen, there will be less depth of field than indicated.
With a given camera, the controls you have over depth of field are focal length, shooting distance and aperture. Depth of field increases as aperture size decreases (i.e., as you stop a lens down). Depth of field increases as camera-to-subject distance increases, and it increases as focal length decreases. Ultrawides have very short focal lengths, which increases depth of field, but they also generally are used at very close range, which, in turn, decreases depth of field.
Diffraction. When light rays travel through an aperture, they tend to spread a bit. The smaller the aperture, the greater the rays spread. This is diffraction, and it reduces image sharpness. Because the ƒ number is the ratio between the diameter of the aperture and the focal length of the lens (e.g., a 100mm lens set to ƒ/4 has an effective aperture diameter of 25mm), wide-angle lenses have smaller aperture diameters at a given ƒ-stop setting than longer ones, and thus tend to exhibit more diffraction effects than longer lenses. So, it's generally best not to stop down past ƒ/8 or ƒ/11 with a super-wide-zoom lens unless you really need the extra depth of field. Shooting with an ultra-wide-angle lens at ƒ/22 will provide lots of depth of field, but overall image sharpness will be reduced due to diffraction—ƒ/22 on a 12mm lens has an aperture diameter of just half a millimeter.