Reversing a lens exploits the fact that standard photographic lenses are optimized to project a large field of view onto a small sensor. When reversed, the optical design is effectively inverted: the lens now projects a very small subject area onto the sensor at high magnification. The lenses you mount together should have the same diameter.

Optical principes

A reversed wideangle lens (e.g., 28–50 mm) produces high magnification because its optical formula is designed to enlarge a small image circle.
Magnification ( M ) for a reversed lens is approximately when used on a bellows or extension system:

Technical characteristics

Working distance becomes extremely short (often 3–5 cm).
Aperture control is typically manual; electronic diaphragms remain closed unless locked.
Field curvature and chromatic aberration increase at extreme magnifications.
Dust exposure is a risk because the rear element faces outward.

Use cases

Extreme macro (2:1–5:1)
Static subjects
Controlled lighting environments

Lesson 02: reverse mounted lenses

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