What size sand skin is used to polish pinhole camera?

The fourth one. The pinhole camera is polished with No.4 sand skin. A camera is a kind of equipment that uses the principle of optical imaging to form an image and records the image with a negative. This is an optical instrument used for photography. In modern social life, there are many devices that can record images, all of which have the characteristics of cameras, such as medical imaging equipment and astronomical observation equipment.