Originally, bellows were an air-tight sack of leather, used to blow air into a furnace. Bellows were also incorporated into musical instruments, like the harmonica, to blow air into the instrument and freeing the player's lungs from this duty. While this type of bellows can be built with a sack of any shape, it is most efficient when built with a series of folds, so that it can be extended in length when full, and fold down to almost nothing when empty.
Most old cameras were built with leather bellows quite similar in shape to that of a harmonica. In these cameras, the purpose of the bellows was not to pump air, but to allow the distance between film plane and lens to change when focusing and when changing lenses. Bellows also allowed cameras to fold down to an almost flat package when not in use, which was useful because those cameras used large negatives or photo-sensitive plates and, once set up for use, were bulky and difficult to transport. The same basic design of bellows is still employed by modern large-format film cameras.
In macrophotography and photomacrography, bellows are used between lens and camera body, and function like a variable extension ring. This type of bellows is the subject of this page. Typical macro bellows (see examples in the figures) allow a minimum extension between lens and camera body of 30-40 mm, and can extend to about 150-200 mm. The mechanical parts supporting the bellows must be sturdy and rigid, and typically are very heavy. The bellows themselves are typically made with a combination of thin leather, leatherette, cloth and/or plastics, and are quite delicate. They must not be crushed, and can be damaged easily by careless handling. In order to protect them, bellows typically are folded to their minimum length when stored. Any light that enters the interior of the bellows through small cuts and holes reduces the contrast of pictures taken with them.
It is also a good idea to fit bellows with front and rear caps when not in use, to prevent dust from entering their interior. Any dust contaminating the interior of the bellows easily moves to the interior of the camera and lens afterwards, because the bellows blow a considerable amount of air when their length is changed.
The Nikon PB-6 bellows, shown above, are typical of good-quality bellows for SLR and DSLR cameras. The same type of bellows can also be used with mirrorless cameras. The large knobs turn the gears. The smaller knobs lock the carriage onto the rail, and can also adjust the friction. Levers at the base of the lens support are used to manually close the diaphragm (there are no provisions for control of the diaphragm by the camera body). A flexible shutter release cord can also be connected to a threaded hole on top of the lens support for the same function (with traditional cameras, a double release cord was used to close the diaphragm and trip the shutter simultaneously). The button near the lens mount is the lens release, the one near the camera mount allows the latter to rotate. This is necessary to mount some camera bodies (including Nikon DSLRs). Consumer-grade Nikon DSLR bodies must use manual exposure when mounted on these bellows.
In most bellows, the supports that hold the ends of the bellows (generally called standards by analogy with the corresponding parts of large-format cameras) allow the bellows to change length by sliding along a metal rail with a prismatic (usually hourglass shaped) cross-section, or a pair of round rods. Often, an additional sliding support is present at the bottom of the rail, and can be used to attach them to a tripod head (see above figure). This rail or pair of rods is usually heavy, but is also delicate and easily damaged by bumping it accidentally on hard objects. Any damage to these parts is likely to prevent the movement of the lens and camera standards, or to make it uneven. The same care must be given to the geared racks used to move the platforms. Also these parts are fully exposed when the bellows are in use. The bayonets that couple the bellows to lens and camera body are also delicate, and should be protected with caps. Therefore, bellows should be treated with at least the same care given to lenses.
The Nikon PB-6, like most bellows with a prismatic rail, use nylon inserts to slide the standards against the rail. In some types of bellows, these inserts (especially if made from white nylon) may crack with age, and these bellows may suddenly come apart when carrying a camera and lens. The nylon inserts also make it easier for the standards to slide smoothly and without catching. However, the inserts also make it difficult or impossible to completely lock the standards at a chosen position, especially if the bellows are mounted vertically. Small amounts of sagging, slow creeping and similar problems are the undesirable results.
Some bellows, like the Nikon PB-6, can be used with accessories for slide and film duplication. The PS-6 slide and film duplicator is shown above, mounted on the PB-6 bellows and the Micro Nikkor 105 mm f/2.8 lens. This particular combination requires the use of extension tubes between camera body and bellows - the PS-6 is actually designed for use with a 55 mm lens. The PS-6 includes also spools (not shown) for holding a film roll.
Using the PS-6 with lenses other than the Micro Nikkor 55 mm requires additional accessories. Longer lenses, like the 105 mm shown above, may require extension rings at the back of the bellows, and may not cover the full 35 mm frame. The Micro Nikkor 60 mm works, but requires a reducing ring to couple its filter mount to the lens mount of the PS-6. An external light source is also necessary to illuminate the opal glass at the back of the duplicator. Illumination must be uniform, and cannot come from a grazing direction, lest the edges of the metal frame containing the opal glass cast shadows.
Once the PS-6 is set up, slide duplication is faster than with a film scanner. However, the PS-6 has no provision for dust removal, and duplicates only one slide at a time. The PS-6 can be used with a DSLR body, but I would not regard it as a viable alternative to a flatbed scanner with slide and film capabilities, or a dedicated film scanner.
Using bellows with reversed lenses is discussed here. The Nikon PB-6 bellows possess a comparable arrangement for doing this as the Olympus OM bellows described at the above link.
In practical use with the bellows oriented vertically, I found that the focusing and locking mechanisms at the bottom of the rail of the PB-6 are not designed to carry the weight of the camera and bellows. The gear rack is especially underdimensioned, and practically useless for focusing with the bellows mounted vertically. It is also not precise enough for focusing in photomacrography at any bellows orientation. For this reason, I removed the bottom focusing platform and its geared rack, drilled and tapped two 1/4-20 holes at the bottom of the rail, and attached a long Arca plate in this position for mounting the modified PB-6 on a macrophotography stand equipped with a much better focusing mechanism. This modification is entirely reversible, and the tapped holes are almost completely hidden when the geared rack is mounted back in its original position.
Nikon provided a PB-6E extension that approximately doubles the maximum extension of the PB-6, making it probably the longest available stand-alone bellows system for 35mm film SLRs (the Leitz Aristophot, Nikon Multiphot and a rarely seen Olympus photomacro/micro stand could be equipped with longer bellows, but are dedicated stand-mounted systems for lab use).
Nikon also made PB-6D risers to increase the height of the rear and front mounts of the PB-6 bellows above the rail. This allows the rear standard to move forward without large camera bodies (like the D4) touching the rail. Two PB-6D must be used on a PB-6, or three if the PB-6 is coupled to a PB-6E.
The PB-6M is a rather narrow base that attaches at the front of the PB-6 rail and allows the bellows to stand up vertically. The PB-6M is an accessory of questionable usefulness, not wide enough to be reassuringly stable, and its use reduces the total amount of available extension of the PB-6.
During the second half of the 20th century, virtually all SLR camera brands were offering bellows, often of good mechanical quality. The situation is different today. The whole range of PB-6 and accessories has been discontinued by Nikon, but Nikon stores and third-party shops may still offer small stocks of left-over accessories. However, the PB-6 bellows are almost exclusively found on the second-hand market. Novoflex is probably the only current maker of high-quality (and expensive) bellows, while China Inc. is flooding the market with low cost, rather poorly made models. The Soviet Union was selling a model of mechanically very roughly made bellows for decades, approximately until it crashed and went under. These bellows were equipped with M42 attachments, and were lubricated with generous amounts of machinery fat to try and hide their wobble and loose tolerances. The pleated "leather" felt more like cardboard than animal skin or fabric. The maximum extension of these bellows was unusually high (290 mm), thanks to a double-stage sliding mechanism (but this forced the pleated mistery material to stretch dangerously tight). Old stocks seem to be still available, and are offered on eBay.
Ihagee/Exakta used to make a couple of models called Vielzweck (usually painted light blue) and Kolpofot (the latter is a medical photography system and usually painted white) of bellows with metal-against-metal sliding surfaces. These bellows are much stiffer and lock more securely than those with nylon inserts. However, they also show a higher tendency to catch or slide unevenly, and can be difficult to modify with suitable front and rear adapters. The standards are mounted on sliders without gears. The geared rack at the bottom of the rail is relatively roughly made, and you will not want to use it for precision focusing. One model has hollow standards, the other massive ones (and this is the most desirable one). This is by far the stiffest type of bellows I know of (with the possible exception of those built into photomacrography stands), and the least likely to suffer from vibration and sagging problems. Unfortunately, the pleated material is often in poor condition, and it may be necessary to replace it with the corresponding part from a cheaper and more recent bellows model (including the China Inc. ones).