| 摘要 |
PURPOSE:To provide a high vignetting factor throughout a screen and shorten the back focus by providing four lens groups and specifying focal length, radiuses of curvature of lens faces, lens thicknesses, and air intervals. CONSTITUTION:A first lens group I which has the convex directed to the object side and has a positive refracting power, a second lens group II which consists of two lenses having positive and negative refracting powers and stuck to each other and has the convex directed to the object side and has a negative refracting power, a third lens group III which has the convex directed to the image surface side and has a positive refracting power, and a fourth lens group IV which consists of two lenses having negative and positive refracting power respectively and stuck to each other and has the convex directed to the image surface side and has a positive reflecting power are provided in order from the object side. In such as case, lens groups satisfy conditions of inequalities where (f), Ri, Di, and Ni are the focal length of the whole of the lens system, the radius of curvature of the i-th lens face from the object side, an i-th lens thickness or air interval, and the refractive index of the material of the i-th lens respectively. Thus, the back focus is shortened with a high vignetting factor throughout the screen.
|
