JPH0414732Y2 - - Google Patents

Description

[Detailed explanation of the idea]

a Technical Field This invention relates to photographic lenses, and in particular
This invention relates to a photographic lens suitable for photographing images on a CRT. b. Prior Art and its Problems Recently, as computers have become more widespread, there has been a growing desire to take photographs as a means of recording images on a CRT. Conventionally, when taking images on a CRT, it was common to use a regular photographic lens or an enlarger lens, but since the CRT has a curved surface, it was originally designed to focus on a flat surface. It was difficult to photograph the entire CRT screen with uniform image quality using a lens designed in this way. c Purpose The purpose of this invention is to solve the above problems,
The object of the present invention is to provide a photographing lens that can photograph images on a CRT with uniform image quality over the entire screen, that is, in which various aberrations when photographing a CRT are well corrected. d Configuration The photographing lens of the present invention includes, in order from the object side, a first lens that is a positive meniscus lens with a convex surface facing the object side, a second lens that is a biconcave lens, a third lens that is a biconcave lens, and a third lens that is a biconvex lens. It consists of four lenses in three groups, with the third and fourth lenses bonded together to form a positive lens. e Example The specifications of the photographic lens of the present invention configured as described above are as follows.

[Table] where f: focal length F _NO : aperture ratio y: image height f _B : back focus r: radius of curvature of each lens surface d: lens thickness or air gap n _d : d-line refractive index of each lens ν _d : Atsushi number f of each lens Effect According to the photographic lens of the present invention explained above, approximately
The aberration diagram shown in Figure 2 shows that each aberration has been well corrected for a CRT screen with a curvature radius of 2000 mm and a protective glass with a center thickness of 10.7 mm.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram showing an embodiment of the photographic lens of the present invention. Figure 2 shows various aberrations when a CRT with a curvature radius of 2000 mm and a protective glass with a center thickness of 10.7 mm is photographed at a magnification of 0.2824.

Claims (1)

[Claims for Utility Model Registration] In order from the object side, the first lens is a positive meniscus lens with a convex surface facing the object side, and the second lens is a biconcave lens.
A lens consisting of four elements in three groups, consisting of a lens, a third lens that is a biconcave lens, and a fourth lens that is a biconvex lens, and the third and fourth lenses are bonded together to form a positive lens, f: focal length F _NO : Aperture ratio y: Image height f _B : Back focus r: Radius of curvature of each lens surface d: Lens thickness or air spacing n _d : D-line refractive index of each lens ν _d : Atsube number of each lens, A photographic lens characterized by having the following specifications. [Table] [Table]