What does Yuedai Black Box mean?

Yuedai black box refers to Canon’s proprietary term, referring to its EF series of interchangeable lenses.

The lens body of this kind of lens is mostly black, so it is called a "black box". It is Canon's first-generation photographic technology product. It records and collects front and rear images separately and transmits them to the electronic device in the developing plate and film holder to receive automatic focus or manual adjustment command signals.

It is a technical mode that controls the functional actions of each component in the lens so that it has functions such as metering and exposure, and operates in conjunction with the host to achieve various shooting effects required.