LENS SYSTEM WITH A INFRARED ABSORBING GLASS

摘要

A lens assembly having an infrared absorbing glass is provided to make a leans system having a short back focal length by using the infrared absorbing glass instead of an infrared blocking filter. A first lens(1) is made of an infrared absorbing glass and has positive refractive power. A second lens(2) is arranged to be separated from the first lens at a predetermined interval and has positive refractive power. A third lens(3) is arranged to be separated from the second lens at a predetermined interval. At least one side of the third lens is an aspherical surface and has negative refractive power. An opening iris(4) is arranged between the first lens and the second lens to prevent unnecessary incident light to an optical system.