Lens mostly refers to a way of mounting Chinese painting sketches or certain decorative paintings. It is mounted on thick cardboard before sale (the color of this cardboard can be elegant or gorgeous, and it is also decorated with broken gold foil, which has a very good effect). When you buy it, you can put it directly in the frame and hang it indoors for viewing. Because lenses come in various forms and are suitable for modern home decoration, there are painters who specially paint them. These unframed paintings are called mirror centers.