Bellows units function as continuously adjustable extension tubes, allowing precise control over the lenstosensor distance. Increasing this distance increases magnification according to:

[ M = \frac{\text{Extension}}{f} ]

where ( f ) is the focal length of the lens.

Optical and Mechanical Behavior

Extension range typically varies from 40 mm to 150+ mm.
Magnification can exceed 3:1 with short focal lengths.
Light loss increases with extension: [ \text{Effective f-number} = f \cdot (1 + M) ]
Mechanical stability is critical; even minor vibrations cause motion blur.

Advantages

Infinitely variable magnification
Compatible with enlarger lenses, reversed lenses, and standard primes
Ideal for focus stacking due to stable, repeatable positioning

Limitations

Bulky and fragile
Not suitable for moving subjects
Requires tripod, rail, and controlled lighting

Lession 03: Bellows

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