Flat lenses can also be called glass plates, such as prisms, reflecting lens manufacturers, Newton used it to discover the dispersion of light, but the light is from the side of the glass. If it is incident from the front, reflecting the lens, the outgoing light only increases a little offset, the outgoing light is parallel to the incident light, and can not converge or diverge, so it is not much use in optics. Flat mirrors can also realize the direction of light, for example, the secondary mirror of the Newton reflecting telescope is a flat mirror, so it is widely used. Flat lenses can also be called glass plates, flat mirrors can also achieve the direction of light, such as the Newton reflecting telescope's secondary mirror is a flat mirror, reflecting lens prices, so it is widely used. When the flat lens is ground, it is considered to be used for interferable light and will not produce stray (scratches, dents, gloss). Specifications include uncoated and coated anti-reflective multilayer lenses with visible light bands. The characteristic of the flat lens is that the focal length of the lens is the distance from the main point to the focus, and its purpose is to converge parallel light.

Flat glass, cover glass, flat glass has good perspective, good light transmission performance (3mm and 5mm thick colorless transparent flat glass visible light transmission ratio of 88% and 86%, respectively), high transmission rate of near red heat rays in the sun, but the visible light set indoor wall top floor and furniture, fabric and reflected far-infrared long-wave heat rays are effectively blocked. Therefore, it can produce obvious "warming effect". Colorless transparent flat glass has low ultraviolet transmittance to sunlight.