What about the single and double sleeves on the SLR camera?

The "single" of a SLR camera (or single battery or micro-single) refers not only to a single lens, but also to a replaceable lens. Photographers can choose the most suitable lens according to different scenes and themes, so a SLR camera is usually equipped with more than one lens.

Commercially available SLR cameras are called stand-alone cameras, and users can buy additional lenses according to their own needs; The fuselage with commonly used lenses is called a setting machine, and the matching lenses are called hoods. Single lens refers to only one lens, and double lens refers to two lenses ... This collocation can be recommended by the manufacturer or matched by the dealer himself. As for what kind of lens to match, you need to know clearly when you buy it.