Magnifiers are simple visual optics used to observe the tiny details of an object, and are converging lenses with a much smaller focal length than the photopic distance of the eye. The magnitude of an object imaged on the retina of the human eye is proportional to the angle (viewing angle) of the object to the eye.
Magnifying glass is also known as fire mirror. A simple optical device that can obtain magnified virtual images. It usually consists of a convex lens and a frame and handle. When used, by placing the object near behind the lens (within the focal length), you can see the virtual image of upright magnification, which helps to distinguish details, and is often used to view specimens, drawings, negatives, photographs, film copies, etc. According to the curvature and the refractive index of the glass used, there are many kinds of magnification, such as 10, 20, 30 times.