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Everything we said about extension tubes also applies to bellows. Their working principle is the same, but using bellows, you can change the amount of extension (therefore the magnification of the system) very easily and precisely.

The formula used to calculate the maximum magnification achieved with bellows is:

where:
ML – maximum magnification of the lens
Еxt – added extension [mm]
F – focal length of the lens [mm]

* When the lens is focused at infinity, ML=0

The other advantage of bellows over extension tubes is that the expensive models have the ability not only to move the lens away from the camera, but also to bend, placing the lens at an angle toward the camera body. This allows the plane, in which the objects are seen sharply, to not be parallel to the sensor plane. This way you can use depth of field in a better way, setting it so, that a larger part of your model lies in it. This method, however, is seldom used in practice. Instead of that, focus stacking is used, which increases the total depth of field in the frame.

Bellows don’t transmit the electric communication between the camera and the lens, except for some of the very expensive models. This makes them easier for use with lenses with an aperture ring. On the other hand, you can easily manufacture a device for transmitting the communication, but you’ll have to sacrifice two extension tubes with electric contacts and a piece of cable in the process.

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