A lens adapter is a device to mount lenses made for some type of camera on another camera for which they were not originally designed.
An adapter will receive any lens with one type of lens mount, and attach it to a camera body with another lens mount. In some cases the use of a lens on an adapter changes the distance range or the speed of the lens.
| lens adapters|
above: 1. M42 thread in Four-Thirds bayonet
2. M42 thread in Minolta SR bayonet
3. M42 thread in Minolta AF bayonet
below: 1. M39 thread in M42 thread
2. Minolta SR bayonet in Four-Thirds bayonet
3. Exakta bayonet in Minolta SR bayonet