What you're looking at is a high-quality, durable, and versatile 31mm Section Aluminum Automatic Macro Extension Tube designed specifically for Canon Eos Ef/Ef-s lenses. This compact extension tube is an excellent alternative to more expensive macro lenses, offering the same functionality at a more affordable price point. This extension tube works by increasing the distance between your camera body and lens, effectively shortening the focusing distance and magnifying your subject. This makes it an invaluable tool for macro photography, product photography, and any other applications requiring a close focusing distance. The Fotodiox Pro Auto Macro Extension Tube for Canon Eos is an automatic tube, meaning it seamlessly communicates all electronic functions from the lens to the camera. This includes both autofocus and auto-exposure, ensuring your photography experience remains smooth and efficient.