Tuesday, February 28, 2012
The ins and outs of a landscape photographer’s most used lens
The point here is that which focal length constitutes "wide-angle" varies with camera format. For 35mm SLRs and full-frame digital cameras, lenses of 35mm and shorter are wide-angle, and lenses of 21mm and shorter are superwide-angle. For an APS-C camera, the equivalent focal lengths would be two-thirds of those for full-frame—wide-angle starts at 24mm and superwide-angle at 14mm. For Four Thirds cameras, the equivalent focal lengths would be half of those for full-frame—18mm for wide-angle, 11mm for superwide.
Exotic Glass Elements
Wide-angle lenses are prone to spherical aberration (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), especially fast wide-angles with their large front elements, so lens designers include one or more aspherical elements to minimize this. Designers also employ extra-low-dispersion elements with such designations as ED, UD, SUD, FLD, SD, LD and SED to minimize chromatic aberrations (different wavelengths of light focusing at different distances behind the lens or at different distances from the optical axis). All of the wide-angle zooms listed in our lens chart incorporate both aspherical and extra-low-dispersion elements.
Distortion & Perspective
In theory, true wide-angle lenses are rectilinear; they reproduce straight lines in the scene as straight lines no matter where they appear in the image frame. In practice, wide-angle lenses, and especially superwide-angle lenses, do bend straight lines near the frame edges: barrel distortion. Fisheye lenses aren't rectilinear; they bend straight lines outward unless those lines pass right through the center of the image.
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