| 摘要 |
PURPOSE:To realize a refraction type optical system having an F number which is lighter than two and a good performance, by satisfying prescribed conditions to the optical system composed of three groups. CONSTITUTION:From the screen side to the projection tube side, the 1st group Icomposed of an aspherical surface plastic single lens of the positive refracting power, whose convex surface fases to the screen side, the 2nd group II composed of a biconvex glass single lens having an X-ray shielding effect, and the 3rd group III composed of an aspherical plastic lens of the negative refracting power, whose concave surface faces to the screen side, are provided successively. They are arranged so as to satisfy the conditions of formulaeIand II. In the formulae, N represents the refractive index of the group II, (f) represents the focal length of the whole system, and the f1 is the focal length of the 1st group I. In this way, a refraction type optical system for video projector having an F number which is lighter than two can be obtained. |
