wide-angle lens - Digital camera issues

A lens that has a wide field angle of view or coverage compared with the standard lens fitted to the camera. Its focal length is less than the diagonal of the film format in use. The standard lens has a field angle of c.52°, and coverage of 55–65°, 65–80°, and 80–110° is given by semi wide-angle, wide-angle, and extreme wide-angle lenses respectively.

In photography and cinematography, a wide-angle lens is a lens whose focal length is substantially shorter than the focal length of a normal lens for the image size produced by the camera, whether this is dictated by the dimensions of the image aperture at the film plane for film cameras (film format) or dimensions of the photosensor for digital cameras. (It is said to be "normal" because a lens of this focal length provides more or less normal perspective.) For example, for a full-frame 35 mm camera with a 36 mm by 24 mm format, the diagonal measures 43.3 mm and by custom, the normal lens adopted by most manufacturers is 50 mm. Therefore, also by custom, a lens of focal length 35 mm or less is considered wide-angle.

Common wide-angle lenses for a full-frame 35 mm camera are 35, 28, 24, 21, 18 and 14 mm. Common focal lengths for these in a 35 mm camera are 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 15 or 16 mm can produce either curvilinear fisheye-like (high barrel distortion) full-frame images or rectilinear full-frame images, depending on the design. For 35 mm cameras, lenses producing rectilinear images can be found at focal lengths as short as 12 mm including zoom lenses with ranges of 2:1 that also begin at 12 mm.

In addition to giving a wider angle of view, the image produced by a wide-angle lens is more susceptible to perspective distortion than that produced by a normal lens.

Digital camera issues

Most interchangeable lens digital cameras today (2006) are in the form of 35 mm cameras. However, most of these cameras have photosensors that are smaller than the image apertures of full-frame 35 mm cameras. For the most part, the dimensions of these photosensors are similar to the APS-C image aperture size, i.e., approximately 24 mm x 16 mm. Therefore, the angle of view for any given focal length lens will be narrower than it would be in a full-frame camera because the smaller sensor "sees" less of the image projected by the lens. The camera manufacturers provide a field of view factor to show the equivalent focal length if the camera had a full-frame sensor. The usual factor is 1.5, indicating that the effective focal length of the lens on the camera is 1.5 times its actual focal length. As examples, a 28 mm lens would produce the angle of view of a 42 mm lens on a full-frame camera, and a 35 mm lens would produce a 52.5 mm angle view, which is not a wide angle view at all. So, to determine the focal length of a lens for a digital camera that will give the equivalent angle of view as one on a full-frame camera, the desired full-frame lens focal length must be divided by the field of view factor. For example, to get the equivalent angle of view of a 28 mm lens on a full frame 35 mm camera from a digital camera with a 1.5 field of view factor, one would use an 18 mm lens.

Lens manufacturers have responded to this problem by making wide angle lenses of much shorter focal lengths for these cameras. At 10 mm, these lenses provide the angle of view of a 15 mm lens on a full frame camera when the field of view factor is 1.5.