JPS6128966B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photographic lens, and more particularly to a Tesser type lens with a rear aperture. Tetsusar-type lenses with a rear aperture are extremely useful in terms of reducing the overall size of the camera and simplifying the lens barrel structure, and have been used in many mid-range cameras to date. However, as lenses become smaller, the following drawbacks tend to occur. (1) At the front surface of the central biconcave lens, which has the function of correcting spherical aberration and astigmatism in the middle part of the incident height, the refraction effect on the off-axis light flux in the part with the maximum incident height becomes excessive, so the intermediate image Coma and flare are larger at the peripheral angle of view than at the corners. (2) In addition, the front surface of a biconcave lens has a strong effect of sharply curving the sagittal image plane in the off-axis periphery in the positive direction, resulting in significant over-correction of the peripheral sagittal image plane or correction of the sagittal image plane in the middle of the screen. There is a tendency for one or the other to become insufficient. SUMMARY OF THE INVENTION An object of the present invention is to overcome the above drawbacks and provide a compact lens with good aberration correction. Therefore, as shown in Figure 1, starting from the object side,
A positive meniscus lens with the convex side facing the object, a biconcave lens, a bonded positive lens made by bonding a biconvex lens and a negative meniscus lens, and an aperture are arranged, the focal length is f = 1, γ is the radius of curvature of the lens surface, and d is The following numerical specifications are satisfied, where the axial thickness of the lens or the air gap, Nd is the refractive index for the d-line, and νd is the Abbe number.

【table】

[Table] Back focus bf=0.7851 Spherical aberration, astigmatism, distortion, and coma aberration for an object at infinity according to the present invention are well corrected as shown in FIG. The third-order aberration coefficients are shown in the table below.

【table】 [Brief explanation of the drawing]

FIG. 1 is a sectional view of a lens showing an embodiment of the present invention.
Figure 2 is an aberration curve diagram. In the figure, γi is the lens surface, di is the lens axial thickness or surface spacing, S is the sagittal image surface, and M is the meridional image surface.

Claims (1)

[Claims] 1. Consisting of, in order from the object side, a positive meniscus lens with its convexity directed toward the object, a biconcave lens, and a bonded positive lens in which a biconvex lens and a negative meniscus lens are bonded together, and when the focal length f=1, γ is the radius of curvature of the lens surface, d is the axial thickness or air gap of the lens,
A Tetsusar type lens that satisfies the following numerical specifications, where Nd is the refractive index for the d-line and νd is the Atsube number. 【table】