Patent attributes
A four-piece lens assembly, from the object side, comprises: an aperture, a first lens, a second lens, a third lens, a fourth lens, a flat parallel glass and an image plane. The first lens is a double convex positive lens. The second lens is a double concave negative lens or a plano-concave lens whose object side surface contacts the image side surface of the first lens. The first and second lenses contact each other in such a manner that the concave surface of the connecting surface faces the object side, and the concave surface (or plano surface) of the second lens faces the image plane. The first and second lenses are made of high refractive index material. The lens assembly not only can ensure a necessary back focus but also can suppress the total length of a portable image taking device.
