Extension tubes are a photography accessory that is used to extend the distance between the lens and the camera's sensor. This allows the photographer to focus on closer objects than the lens would normally be able to focus on, resulting in a closer, more detailed image. Extension tubes are hollow tubes that are attached between the lens and the camera, and they do not contain any optical elements. Instead, they simply extend the distance between the lens and the sensor, allowing the lens to focus on objects that are closer than it normally would be able to. Extension tubes are a useful accessory for macro photography, where photographers need to be able to focus on very small objects.