JPS58149017A - Inverted galilean type albada finder having short overall length - Google Patents

Abstract

PURPOSE:To shorten the overall length of a finder optical system by introducing aspherical faces to the shapes of lens faces in order to assure the degree of freedom in correcting aberrations. CONSTITUTION:A titled finder consists of the negative 1st lens, the negative 2nd lens having strong curvature on the pupil side and the positive 3rd lens, successively from an object side, wherein a pupil is placed behind the same. A frame of a field range is provided on the object side face of the 3rd lens and the pupil side of the 2nd lens is constituted as a semitransparent concave mirror. The faces of the 1st, the 2nd and the 3rd lenses on the pupil side are formed into the aspherical shapes expressed by the equationIwhen (c) is defined as paraxial curvature, (k) as the coefft. of quadrics, A4, A6, A8 are defined as the coeffts. of aspherical faces of higher order, and (y) is defined as the height from the optical axis, wherein the quartic coefft. of (y) is expressed by the equation II in consideration for the contribution by the coefft. of quadrics. The aspherical face of the rear face of the 1st lens in this case is so formed as to satisfy the conditions of the equation III, the aspherical face of the rear face (half mirror part) of the 2nd lens, as to satisfy the equation IV and the aspherical face of the rear face of the 3rd lens as to satisfy the equation V, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reverse Galilean element finder having a short overall length and having an Albada element system.

In recent years, as cameras have become smaller, master lenses for taking photographs have become smaller, and finder optical systems have also been required to have small gongs. It goes without saying that the key to downsizing the finder optical system is to shorten its overall length. 5. The present invention aims to provide a finder with a short overall length that is comparable in visibility to conventional finders. Concrete (Ha finder @ thing 0.57, Hangatou 27
The target is a reverse Galilean optical 7-inder incorporating the Albada optical system.

If you try to shorten the overall length with this mallet finder,
In order to have a predetermined finder efficiency, the refractive power of each lens must be made strong, which makes it difficult to correct aberrations.

In normal designs, when the refractive power of a lens becomes strong and aberration correction becomes difficult, it is common to increase the number of lenses and make each lens have a fractional refractive power. It is unsuitable for a finder optical system like the present invention.

In other words, there are seven ways to view the subject using the master lens.
If it is a finder system, it is possible to use the method of increasing the number of lenses as described above, but as in this study, it is possible to incorporate the Albada optical system into a full-length pheasant 7-inder.
In addition, by increasing the number of lenses, the distance between the half mirror and the frame 11, which is already narrow, is further shortened, and the expected angle of incidence b on the half mirror is reduced;
When it became a big production, the frame of the Arvada optical system became distorted (the curvature of the image plane became too severe, making it unusable for practical use).

The basic configuration of the finder of the present invention is a front static double lens, fk#', which is commonly used in intermediate-level cameras.
A type consisting of one positive lens is adopted.

In this type, the parameters of the optical system are largely determined by the first-order refracting force arrangement to simultaneously establish the finder system and the Albada system, and the free Ij that can complement the aberration correction.
E is not very small. In the present invention, this free hiding is achieved by
As shown in the data table below, we introduced the lens shape Vζ in order to 'a31 m (Ll, S, Pm3575
1182) to 27.6m (% open 115u-275
Compared to 3981@lJt, it is set to flat.

Also, revenue! ! ! Regarding correction, the finder system has a total of ms
'ic must be corrected, but for the Albada system, it is only necessary to correct the distortion in the angle of view of the frame, and there is no need to correct the angle of view at all angles of view. Moreover, since frame-shattering aberrations can be canceled out by the shape of the frame, they can be excluded from the scope of aberration correction.

Following the basic configuration described above, the finder optical system of this study consists of a negative lens from the object and a negative meniscus lens with strong curvature at the pupil, as shown in Figure 1. The second lens consists of a third lens with a positive recurve, and behind it is a Carriolean optical finder with an m device to clearly show the breaking range of the master lens on the moving object @ circle of the third lens. The so-called Albada optical system is constructed by using a semi-concave convex mirror as the focal point of the second lens.
gi, 2nd. The mii* surface of the third valley lens is an aspherical surface.

Non-spherical shape with C paraxial curvature 111t quadratic surface coefficient A4. It is assumed that A6 and A8 are respectively imposed by higher-order aspherical coefficients y and 1I16 from the optical axis, and 2 is expressed as y's fourth-order coefficient, taking into account the meridian from the quadratic curved surface coefficient.

At this time, the aspheric surface of the rear circle of @l lens is △ 1, tlXl(J″″5<An<b, uxlu-5,,
, t, 1) For the aspherical surface of the second lens rear surface (half mirror) -3,5XIU-5(7';54(-1,uxlo-5
,,,t2) For the aspherical surface of l after the third lens, 2, tl X l O""<Q4<4.5 X l
tJ-5・'3) are satisfied.

Condition jl) is the rear surface of the lens, and the aspherical shape is set so that off-axis curvature is stronger than paraxial curvature, and the purpose is to correct the off-plane curvature of the finder system. This is because the curvature of the off-axis is made weaker than that of the paraxial in order to correct distortion aberration (Japanese Patent Publication No. M52-41tJ56). When the aspherical coefficient becomes smaller beyond the lower limit, the 1# surface becomes larger in the direction of positive diopters.
If the value exceeds the upper limit, the distortion becomes too stringy.

Ant bond '2) is related to the backward direction of the second lens, and is to set the valve ball l11fi sugifu so that off-axis curvature is weaker than the curvature near the paraxial axis. This surface is a surface that affects the accuracy of both the viewfinder system and the Albada system, and when the upper limit is exceeded, it is important to suppress the occurrence of coma aberration in the Albada system, and when the lower limit is exceeded, When the valve ball If [i note becomes thicker, in the case of the Albada series, the palm surface becomes more negative diopter, and at the same time, in the finder thread, the bride surface becomes more positive diopter, and the deterioration of the pigeonhole and b ability occurs.

Condition I, 3) relates to the backward orientation of the third lens,
The aspherical shape is set so that the curvature is sharper off-axis than near the paraxial area. This aspect also has a negative impact on the alignment correction of both the finder system and the Albada system.

Article I4: <3) is a necessary condition to suppress the occurrence of Albada coma aberration, and if this lower limit is exceeded, the occurrence of Albada extroverted coma becomes unsightly; on the contrary, if the upper limit is exceeded, As the bulb diameter increases, the sag of the bulb in both the viewfinder and Albada systems increases in one direction in the positive diopter, and the viewability of the finder deteriorates.

It is desirable that the following conditions be satisfied to the east of the pond in the three conditions above.

Regarding the aspheric surface of the Luns tlk surface, /\ 2, LI X l tl"" (A6 (1,5X I
U"" ... 14)/\ Here, it is the coefficient of habituation of y in the formula expressed in the A6Vi non-spherical circle'1, and the contribution from the quadratic curvature direction pole number k is also taken into account.

Is this condition an article? The purpose is to assist in '1-1) and perform one-plane correction for the finder system. The influence of this condition is especially noticeable in large-scale paintings and ceramics. The F limit is the limit for producing this effect, and the upper limit is the limit for preventing barrel distortion from increasing.

Examples of the present invention will be described below, and FIGS. 2 to 9 show aberration diagrams of the finder threads of actual fmflll to Example 3 and aberration diagrams of the Albada system separately. As a friend, the aberration diagram is with the heel at 4-.

Example I W=27 Finder @ rate 0.57 However, it is @7 side Vi pupil.

f = -571J fB = -99 (J cutting -1゜oi diopter △ $2 A4 = 3□L123X□. -5 total 6 = 7.16
69XIU-'△ Stirring 4 A4=-2,39128xlu-5△ Eye 6 A4 =2.7575XllJ-50 Implementation row 2 W=27 However, 7-sided Vi-0 f=-57Ll Import=-983 View 11: = -1, (32 Dionota-/\ △ $2 A4-4.3 (J5XIU-5A4=LIJ5
L) 2XIU-'△ 114 A4=-1,764uX10-5△ $6 A4=2.7812X1tl-5 Example 3
W=27 Finder magnification=0.62 However, the 7th surface is the pupil.

f=-571 fB=-922 diopter"-1,138 diopter△
-5△ 薯2 A4=1.819Xlt) A6=2.9
495XIO- to 4 A4 =-2,166XIU-5△ $F6 A4 =3.392Xlu-5*va9%+
4W-27 However, the 7th surface is - f=-499 fB=-999 diopter=-1, (J diopter △ stirring 4 A4=-3, 154XlO-'△ i A4 = 2.395X1 (J"-'

[Brief explanation of the drawing]

FIG. 1 is a sectional view of Example 1. Figure 2 is a convergence diagram of the finder system of Example 1. Figure 3 is
Figure 4 is the Albada system aberration diagram, and Figure 5 is the finder system aberration diagram of Example 2.
Albada system Figure 6 is a diagram of finder system aberrations of Example 3. Figure 7 is a diagram of Albada system Figure 8. Vi Finder thread aberration of Example 4. Figure 9 is a diagram of Albada thread aberrations of Example 4. Patent applicant Rokuyo Konishi goes to Daijo to work for Kogyo Niji company
Patent Attorney S - Male (1 person) Figure 3: Sine curvature of field at the exit angle Figure 4: Sine curvature of field at the exit angle Distortion Figure 5: Sine curvature of field at the exit angle Figure 6: Sine curvature of field at the exit angle Sine curvature of field Distortion Fig. 7 Sine curvature of field at the exit angle Fig. 8 Sine of the exit angle -4-202J-3Q3 D-2 curvature of field Distortion aberration Fig. 9 Phantom curvature of field at the sine of the exit angle 5in9'=0.242 sinσ=0.146

Claims (1)

[Claims] An inverted Galilean type finder consisting of, from the object side, a negative lens, a negative meniscus second lens with a strong curvature in 1iiilll, and a positive third lens, and a pupil after the lens. In a finder configured with an Albada system, a claim frame indicating the field axis 8t is provided on the object side of the 3rd lens, and the pupil side thi of the lI2 lens is a semi-transparent concave mirror. is an aspherical surface, and the aspherical shape is given by the curvature of the near circle cVi, which is a quadratic surface coefficient, A4゜A6
．． A8 is a higher-order aspherical coefficient, y is I from the optical axis
1.0XILI-5<total 4〈6υX1O-''5 for the aspherical surface of the rear surface of the second lens -3,5XIO-5 <A4<-1, uXIU-'2, uxlu-5('Qa <4,5xlu-5ffr
A reverse Galilean Albada finder whose enemy is adding s.