JPH0448205B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an eyepiece lens, and particularly to an eyepiece lens suitable for use in an electronic viewfinder of a video camera. [Background of the Invention] As video cameras have recently become smaller and lighter, CRT tubes for observation have also become smaller.
That is, the size of the effective screen of the CRT tube, which is the surface to be observed, is also becoming smaller. Moreover, even if the screen becomes smaller, the image observed through the eyepiece must be as large as the image observed on a CRT, which used to have a large screen. Incidentally, the ratio of the image to be observed to the image observed through the eyepiece, or the magnification of the loupe, becomes smaller as the effective screen of the CRT tube becomes smaller, the higher the eyepiece is required. Generally, the focal length of the eyepiece to obtain an observation image of the same size is the size of the observed surface (length and width)
is inversely proportional to Therefore, when using an eyepiece with high loupe magnification, the focal length is short, but the distance from the eyepiece to the observer's pupil position (hereinafter referred to as ``pupil distance'') is sufficiently long. It is necessary to configure the lens. In addition, when a reflective mirror is placed between the observed surface and the eyepiece, or when the entire eyepiece is moved back and forth on the optical axis to adjust the diopter, the distance from the eyepiece to the observed surface ( This distance (hereinafter referred to as ``back focus'') must be taken seriously. However, in order to satisfy this condition while maintaining the focal length, the construction of the eyepiece lens generally becomes complicated and large. Furthermore, while the focal length of the eyepiece is short and the refractive power is strong, if the pupil diameter of the observer is assumed to be constant, the aperture ratio of the eyepiece becomes large, making it extremely difficult to correct aberrations. [Object of the Invention] The present invention has been made in view of the above-mentioned technical background. That is, the present invention has a simple configuration, and when the magnification of the loupe is approximately 6.5x to 7.5x and the focal length is f, the back focus is 0.85f to 0.95f, and the pupil distance is
The objective is to provide an eyepiece lens that achieves good aberration correction of about 0.9f to 0.8f. [Summary of the Invention] In order to achieve the above object, the gist of the present invention is to bond a _first lens whose both lens surfaces are convex and a _second lens with negative refractive power in order from the subject side. f is the focal length of the entire lens system, L is the length of the entire lens system on the optical axis, and Ri is the i-th lens in order from the subject side. Radius of curvature of the surface, N _P , N _N
The refractive index of the medium of the 1st _1st lens and the 1st _2nd lens, respectively,
When ν _P and ν _N are the Atsube numbers of the _1st lens and the _12th lens, respectively, 0.29<L/f<0.4 (1) 2.6<R ₁ /f<4.0 (2) 1.0<|R ₃ /f ｜＜2.35 (However, R ₃ <0) (3) 1.05＜R ₄ /f＜5.7 (4) 0.05＜N _N −N _P (5) 15＜ν _P −ν _N (6) Above (1) or An eyepiece lens that satisfies the condition (6). Next, the technical meanings of conditions (1) to (6) above will be clarified. Generally, if the thickness of the entire lens system is increased, it becomes easier to correct aberrations, but it becomes difficult to obtain a long back focus and a long pupil distance. In order to achieve a good balance between long back focus, pupil distance, and good aberration correction, it is preferable that condition (1) be satisfied. If the thickness of the entire lens system exceeds the upper limit of this condition, it will be difficult to obtain a long back focus or pupil distance, and if the thickness exceeds the lower limit, it will be difficult to correct aberrations, especially good correction of field curvature. Condition (2) is a condition for obtaining a long pupil distance and maintaining good aberration correction.If the upper limit value is exceeded, field curvature will occur, and if the lower limit value is exceeded, a sufficient pupil distance will not be obtained. Spherical aberration is also likely to occur. Condition (3) is a condition for correcting spherical aberration and field curvature in a well-balanced manner; if the upper limit is exceeded, the spherical aberration becomes good, but significant field curvature occurs, and it must be corrected with other surfaces. If the lower limit is exceeded, spherical aberration becomes large and correction becomes difficult. Condition (4), like condition (3), is a condition for achieving a good balance between spherical aberration and field curvature, and in particular is a condition for correcting spherical aberration while maintaining a good image plane. When the upper limit value is exceeded, the curvature of field becomes large, and when the lower limit value is exceeded, spherical aberration occurs significantly. In the eyepiece lens of the present invention, spherical aberration and chromatic aberration are favorably corrected by providing a bonding surface on the first lens and satisfying conditions (5) and (6). If the difference in refractive index before and after the bonded surface of the first lens does not satisfy condition (5), the eyepiece as a whole has a strong positive refractive power, so a strong diverging surface cannot be obtained and spherical aberration will be insufficiently corrected. Further, condition (6) is a condition for satisfactorily correcting longitudinal chromatic aberration and lateral chromatic aberration at the same time under the above-mentioned conditions, and if this condition is deviated from, it becomes difficult to correct the above-mentioned chromatic aberration. According to the present invention, by satisfying the above conditions (1) to (6), it is possible to obtain an eyepiece lens that has a long back focus and pupil distance, is compact, and has good aberration correction. Next, some numerical examples of the present invention will be shown. In these numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the thickness of the i-th lens from the object side, and νi is the air distance Ni, νi is the radius of curvature of the i-th lens surface from the object side. These are the refractive index and Atsube number of the lens. For reference, the values of each example corresponding to the conditional expressions related to the present invention are shown in the table below.

【table】

〔Effect of the invention〕

According to the present invention, by adopting a configuration that satisfies the above-mentioned conditions (1) to (6), it is possible to obtain a compact eyepiece lens in which aberrations are well corrected.

[Brief explanation of the drawing]

1, 2, and 3 are cross-sectional views of lenses corresponding to numerical examples 1, 2, and 3 of the present invention, and 4.
, FIG. 5, and FIG. 6 are various aberration diagrams corresponding to numerical examples 1, 2, and 3 of the present invention, respectively.
S and ΔM indicate a sagittal image plane and a meridional image plane, respectively.

Claims (1)

[Claims] 1. Consisting of, in order from the subject, a _first lens having both lens surfaces convex and a _first lens having a negative refractive power, and a second lens having a positive refractive power, f
is the focal length of the entire lens system, L is the length of the entire lens system on the optical axis, Ri is the radius of curvature of the i-th lens surface from the object side, and N _P and N _N are the 1st _{and 1st} lenses, respectively.
1 When the refractive index of the medium of _{the 2nd} lens, ν _P and ν _N are the Abbe numbers of the medium of the _1st lens and the 1st _2nd lens, respectively, 0.29<L/f<0.4 (1) 2.6<R ₁ /f< 4.0 (2) 1.0＜｜R ₃ /f｜＜2.35 (however, R ₃ <0) (3) 1.05＜R ₄ /f＜5.7 (4) 0.05＜N _N −N _P (5) 15＜ν _P − ν _N (6) An eyepiece lens characterized by satisfying the above conditions (1) to (6).