We have developed a wide-angle projection lens with a short projection length which is composed of three plastic lens elements and one glass lens element. To solve the problem of field curvature which is the most important problem in wide-angle optical systems, we developed a projection CRT with an a spherical phosphor surface. The features of the projection TV with this optical system are as follows.
1) It is a slim set with a single mirror system.
2) As the focal length of this lens is short, color aberrations are small and good focusing characteristics are achieved.
3) Thermal drift of focusing characteristics is decreased by using a weak plastic lens besides shortening the focal length.
4) Flare induced by the curved phosphor surface is eliminated by optimum design.
5) We have also developed a new screen for this optical system.
