Bellows  

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 is still employed by modern large-format film cameras.

In macro photography, 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.

Nikon PB-6 bellows. The large knobs turn the gears. The small 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 allow it to change its length by sliding along a metal bar with a prismatic cross-section, or a pair of round rods. Often, an additional sliding support is present on the bottom surface of the bellows, and can be used to attach them to a tripod head (see above figure). This prismatic bar 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 platforms, 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.

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.