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Tuesday, October 25, 2011

Ultra-Wide-Angle Zooms

Create dramatic and dynamic landscape images when you explore the ultrawide end of the spectrum

Labels: LensesGear

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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