Lens tube extensions are available for many lens mounts of modern camera systems. The simplest are the macro rings. The extension can be mounted on the camera's lens mount, and then the lens on the extension's own lens mount. This construction enables the photographer to shorten the smallest distance of the image subject to the front element of the lens.
|A sketchy profile of a camera without and with lens tube extension,|
Lens tube extensions might have facilities to transmit the aperture release shift from the camera.
|Exa's reverse aperture transmission concept: The levers on the|
for extendable extension tube, see helicoid