Lens Types
Lenses are divided into types, by focal length. These types—normal, short, and long, are based on camera format, so the same length lens may be long for a 35mm camera, but normal for medium format. Confusing at first, but not too complicated. Additionally, we have zoom lenses, which are multiple-focal length. The focal lengths discussed below are for 35mm format.
Normal Lenses
For 35mm format the standard normal lens is 50mm in focal length. The term ‘normal’ derives from the approximation of our vision. The angle of view of a 50mm lens is about 60º, close to our own (human) visions.
Short Lenses
Short, or wide angle lenses, are anything shorter than 50mm, for 35mm format. Common focal lengths are 35mm and 28mm. Short lenses are available down to 14mm, referred to as a fisheye.
As lenses get shorter, edge distortion becomes much more apparent. Even the 50mm is a bit short for portraiture. A 14mm lens will have gross distortion on the edges, although it will have a very wide angle of view (114°).
Short lenses also have a greater depth of field at a given ƒ-stop and distance than a longer lens.
Long Lenses
Long, or telephoto lenses, are (correspondingly) any lens with a focal length greater than normal, which is greater than 50mm for 35mm format. Common lengths are 85mm and 105mm. Much longer telephotos are available (600mm +), usually used by wildlife and sports photographers, and our friends the paparazzi.
The long lens compresses apparent distances (near-to-far appears shorter than it is), and they have proportionally less depth of field than normal (again, at a given ƒ-stop and distance).
Of note for 35mm format are lenses in the 90-105mm range, referred to as portrait lenses. These allow ‘head shots’, or portraits from the shoulders up, to be taken without the distortions of a normal lens.
Macro/Micro
Macro and micro lenses are lenses which have additional elements which allow closer focusing. A standard 50mm lens can only focus up to about arm's length, maybe 30 inches. The Nikon 60mm Micro, a lens commonly used in forensic and scientific photography, has a minimum focusing distance of 8 3/4 inches, compared to 1.5 feet for their 50mm standard lens, and 3 feet for their 105mm lens.
Zoom Lenses
Zoom, or multi-focal-length lenses, come ain a wide variety of sizes. Some standards are 28-80mm and 70-200mm, with many shorter, longer, and in-between. Zooms are a good compromise when more than a fixed standard lens is needed. Having the two sizes above pretty much covers most needs.
Due to the very nature of zoom lenses, with one lens doing the work of several, the case can be made that zooms are inherently of a lesser quality than a fixed-length lens, but advances in both design and manufacturing have made this argument less substantial. It is of consideration that the zoom have a smaller spread—you are probably better off with the 28-80 and the 70-200 than a single 28-200.
Specialty Lenses
Of note in this category is the shift lens, used for architectural photography, which corrects (or helps correct) parallax error. In simpler terms, this lens helps keep vertical parallel lines parallel, instead of converging. There are also flat-field lenses, which have little depth of field, which are generally used for copy work and forensic or scintific photography.
