Patent ID: 7986464

Claim:
An image system, adapted to a projection display apparatus for projecting an image beam provided by a light valve of the projection display apparatus onto a screen of the projection display apparatus, the image system comprising: a first lens group, having a negative refractive power and comprising a first aspheric lens, a second aspheric lens, a first lens, a second lens, and a third lens arranged in order, wherein said first aspheric lens and said second aspheric lens each have a negative refractive power, and said first lens, said second lens and said third lens each have a positive refractive power; a second lens group, having a positive refractive power and disposed between the first lens group and the light valve, the second lens group comprising a third aspheric lens having a positive refractive power and nearest to the light valve in the second lens group, wherein a material of said third aspheric lens of the second lens group comprises glass, the thermal-optical coefficient of the glass is between 1.0×10 −6 /K and 12.5×10 −6 /K, and the refractive index of the glass is between 1.482 and 1.847, wherein said third lens is disposed between said second lens and the second lens group; an aspheric reflector, disposed on a transmission path of the image beam and located between the first lens group and the screen for reflecting the image beam passing through the first lens group and second lens group; and a curved reflector, disposed on the transmission path of the image beam and located between the aspheric reflector and the screen for reflecting the image beam reflected by the aspheric reflector onto the screen; and wherein said third aspheric lens is a cemented lens.