Different length tubes can be used for a variety of working distances. However, the added distance between lens and film requires additional exposure. Nonautomatic tubes are available, but the automatic variety is far more desirable because it incorporates the advantage of automatic, meter-coupled exposures. Extension tubes also have the feature of accommodating different focal length lenses. Thus, it is possible to use a short telephoto lens, such as a 100 mm lens, on an extension tube to provide a large image when you can't operate too close to the subject.
Bellows are expensive and generally are used extensively for photomacrography.
This is a special lens designed to produce very sharp images at very close subject distances. The usual focal lengths are 55 mm and 100 mm, with the latter being preferred by the experts since it prevents being right on top of the subject. Zoom lenses with macro capability are zoom lenses that can be shifted into close-up capability. In other words, they are not really suitable for photographing extremely small subjects.