Bellows , a concept that comes from the Latin follis , can be used to refer to the device that allows air to accumulate and then expel it in a specific direction. These instruments usually consist of a container with flexible skin on its sides, a valve that allows air to enter, and a barrel through which, when the sides are folded and the volume of the device is reduced, the air escapes.
Bellows, in short, are mechanical devices that store air and then, when subjected to a certain pressure , expel it for a certain purpose. This object inflates when air enters its structure and deflates when it is released.
Generally, the bellows has a valve that prevents the return of the expelled air, although it can also have different openings for entry and exit. Its operation is similar to that of a pneumatic pump.
In the field of metallurgy, bellows are used to blow air into the fuel, increasing the amount of heat and the level of combustion. The forge used when forging metals, for example, has a bellows to fan the fire.
Musical instruments such as the bandoneon , accordion , pipe organ , and certain bagpipes also have bellows. In these cases, the device contributes to providing air or regulating the air expelled by the musician by blowing.
In the field of photography , finally, the bellows is an accessory that is used in certain cameras to facilitate the movement of the lenses and facilitate focusing. These bellows, which fold and expand as needed, create a dark space between the lenses and the film or plate.
The bellows are part of a group of accessories in which the extension tubes or rings are also found. It is an ideal complement to the lenses used to take close-up photographs . A close-up photograph is known as photography that brings the object closer and makes it larger, thus improving the observer's appreciation of its details. Thanks to this type of capture, humans can see certain features of the world around them that usually go unnoticed by them.
Although bellows and extension tubes are different pieces, each with its own characteristics and purposes, their operation is quite similar. For example, both are located between the lens and the camera so that the distance between the focal plane and the subject to be captured increases. Through its use you can go below the minimum focus distance limit, thanks to which the object takes up more space than it normally would.
One of the main differences between extension tubes and bellows is that the latter allow the user to adjust the degree of separation between the lens and the camera body. To do this, they usually have a highly precise mechanism that consists of metal bars on which the lens moves every time we turn knobs in the desired direction, depending on whether we want to bring it closer or further away.
Something that both accessories have in common is that they can retain the automatic features of the camera, although this varies depending on the model and has a considerable impact on the price. The extension bellows are sold with a plug that allows inserting a double release cable, which activates the shutter and the diaphragm at the same time, so that the diaphragm can be kept open to focus and closed at the time of shooting.