Special-Purpose Lenses

A number of lenses exist that do not fit into the traditional wide-angle, medium,
and telephoto lens categories.

Fisheye Lens
For the widest of wide-angle views, consider the fisheye lens. Super wide-angle lenses
allow the photographer to get very close.
A fisheye lens has a very wide angle of view—up to 180°—and exaggerates to an
extreme degree differences in size between objects that are near to the camera and
those that are farther away. Inherent in its design is barrel distortion, an optical aberration
that bends straight lines into curves at the edges of an image. Two types of
fisheye lenses exist:
■ True fisheye. A circular image is taken and the rest of the frame is black.
Literally, a circle is all you get.
■ Full-frame fisheye. The fisheye lens fills the entire frame. Distortion still
occurs, but the frame has no black, blank areas.
Fisheye lenses also produce great depth of field. Objects within inches of the lens and
those in the far distance will be sharp. It is not a lens for every situation, but it can
produce startling and effective views.

Macro Lens
A macro lens is useful for extremely close shots. The lens allows you to focus at a very
close range (see Figure 4.7) and is corrected for aberrations that occur at close focusing
distances. The lens is occasionally called, somewhat inaccurately, a micro lens.
Some zoom lenses come with a macro feature. They focus closer than normal, but
not as close as a fixed focal-length macro lens.

Soft-Focus Lens
Aberrations are deliberately introduced in a soft-focus lens, also called a portrait lens.
The goal is to produce an image that will diffuse and soften details such as facial
wrinkles.

Perspective-Control Lens
A perspective-control lens brings some view/camera adjustments to other types of cameras.
The lens shifts up, down, or sideways to prevent the perspective distortion that causes parallel lines to tilt towards each other if the camera is tilted. Before Photoshop, these lenses were the only way 35mm and medium-format architectural
photographers fixed the distortion of buildings. These lenses are now essentially
obsolete because you can fix the problem in Photoshop.

Catadioptric (Mirror) Lens
A catadioptric lens (also called a mirror lens) is similar
in design to a telescope. It incorporates curved mirrors
as well as glass elements within the lens. The result is
a very long focal length that is smaller and lighter
than a typical lens of equivalent focal length.
These mirrors come into vogue and then fall back
out again every few years. These lenses are the
smallest telephoto lenses you can buy, but they
have some issues. The front mirror in the lens has
the unusual effect of causing out-of-focus highlights
to take on a donut shape, rather than the
usual disk shape produced by an ordinary lens.
Mirror lenses are also slow because of a fixed aperture.
The aperture is usually f/8 or f/11.