JPH0690360B2 - Magnification conversion type reverse galileo finder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aberration correction of an inverted Galilean finder used in a compact camera or the like, and in particular, a finder in which magnification can be switched.

(Background of the Invention) In a camera having a variable focal length objective lens,
It is desired that the shooting range in the viewfinder be switched according to the change in the angle of view of the shooting lens. Conventionally known methods for changing the shooting range are a method of changing the size of the field frame and a method of changing the magnification of the finder. The method of changing the size of the field frame has a drawback that the apparent field of view becomes smaller as the angle of view becomes narrower, making it difficult to observe and lacking power. Also, with the method of changing the magnification as a finder, it is possible to keep the apparent visual field of the shooting range constant, and it is possible to observe with a feeling close to the actual shooting screen, but moving the lens for zooming There was a problem that the amount was large. And as a magnification switching type finder, for example, US Pat. No. 2,755,70
In the specification No. 1 and JP-A-53-63014, a negative refractive power objective lens on the object side in an inverse Galileo finder is composed of a positive lens and a negative lens, and magnification conversion is performed by moving the negative lens. Although a configuration is disclosed, in order to reduce the displacement of the negative lens in such a configuration, it is necessary to make the refracting power of the negative lens extremely strong, and as a result, the deterioration of aberration that tends to occur. In order to prevent this, the total length of the finder has to be lengthened, and it has been difficult to realize a finder having a small structure.

Further, in a camera finder, it is desired to set the total length of the finder to be equal to or shorter than the thickness of the camera body. With recent viewfinders, it is desired to simultaneously display a large amount of information such as the field of view frame, the range-finding range indication frame, the shooting distance display, and the appropriateness of the exposure amount within the field of view. A member requiring a space such as a transmission mirror is often added, and it is desired to minimize the space occupied by the objective lens in the optical axis direction within the limited total length. However, if it is attempted to increase the range of zooming while maintaining a compact shape and to reduce the amount of movement of the lens required for zooming, the refractive power of the lens becomes large, which causes aberrations. Since it tends to become remarkable, it is extremely difficult to maintain excellent performance at all times because of its small size and few aberrations due to zooming.

(Object of the Invention) Under the above circumstances, an object of the present invention is to solve the above-mentioned drawbacks and to reduce the amount of lens movement associated with magnification conversion, and particularly to provide an eyepiece lens side space for various visual field displays. It is an object of the present invention to provide a reverse Galileo finder which is large in size, small in size, and capable of magnification conversion, in which various aberrations are well corrected.

(Outline of the Invention) The present invention is basically based on the magnification conversion type inverse Galileo finder disclosed by the same inventor as the Japanese Patent Application Nos. 59-22565 and 59-22566. The present inventors have found appropriate conditions for properly correcting various aberrations in various states of zooming in this type of viewfinder.

That is, the reverse Galileo finder disclosed in the above-mentioned prior application has negative refraction in order from the object side as shown in FIG. 1A (low magnification state: for wide-angle lens) and FIG. 1B (high magnification state: for telephoto lens). An objective lens group having a power and an eyepiece lens Le having a positive refractive power arranged at a predetermined distance from the objective lens group, the objective lens group having a negative lens component Lb for low magnification. From a second objective lens L ₂ for high magnification having a first objective lens L ₁ , a negative lens component Lc and a positive lens component La added to the first objective lens for low magnification on the object side thereof. Made of The composite negative refractive power of the second objective lens L ₂ for high magnification is the first objective lens for low magnification.
Less than the negative refractive power of L ₁ . And the low magnification first
Low magnification state in which the objective lens L ₁ is arranged on the same optical axis as the eyepiece lens Le, and high magnification state in which the second objective lens for high magnification L ₂ is arranged on the same optical axis as the eyepiece lens Le And were selectively constructed.

And according to such a basic configuration, as shown in FIG. 1B,
Since the second objective lens L ₂ for high magnification is composed of the positive lens component L _A and the negative lens component L _C , the second objective lens L ₂ is substantially the same as the conventional one while maintaining a large axial distance between the second objective lens L ₂ and the eyepiece lens Le. It can function as a high-magnification objective lens L ₀ . Therefore, during zooming, the eyepiece lens side space in the viewfinder can be secured larger than that of the conventional one, and various displays can be performed within the field of view of the viewfinder.

When changing the magnification, the first objective lens for low magnification is used.
L ₁ and the second objective lens L ₂ for high magnification may be provided so as to be convertible, but the negative lens component Lb in the first objective lens for low magnification Lb
Is also used as the negative lens component Lc in the second objective lens for high magnification, the negative lens component is moved to the eyepiece side, and the positive lens component L _A is arranged on the object side to achieve a high magnification state. It can also be achieved.

The basic configuration will be briefly described below. Now, ₁ viewfinder magnification of the high magnification state _beta, focal length f _o of the high-magnification objective lens L _0, focal length f _e of the eyepiece _Le, mainly the objective lens L ₀ and the eyepiece Le for high magnification when the point interval is d _1, the finder system for simplicity assuming the form an afocal _{system, β 1 = -f o / f} e d 1 = f o + f e is satisfied.

Next, ₂ finder magnification low magnification state _beta, a focal length f ₁ of the low-magnification objective lens L _1, when the principal point distance between the objective lens and the eyepiece and d ₂ in the low magnification state, beta ₂ = −f ₁ / f _e However, from β ₁ > β ₂ d ₂ = f ₁ + f _e , By substituting ,, The value of f _o is, by substituting the expression in the formula, By the formula, Becomes Under the condition of 0 <β ₂ <1, β ₁ / β ₂ > 1, d ₂ −d ₁ > 0, and if the magnification ratio β ₁ / β ₂ of the finder is fixed, _The smaller the value of ₂ , that is, the smaller the finder magnification in the low magnification state, the smaller d ₂ −d ₁ . Conversely, if the value of d ₂ −d ₁ that has a large effect on the occupied space in the optical axis direction of the objective lens is restricted to a certain value or less, the value of β ₂ will be specified, and in the past, the value of β ₂ It was only a small viewfinder with a small apparent field of view. Further, the formula 'also shows that the larger the value of the viewfinder magnification ratio β ₁ / β ₂ is, the more d ₂ −d ₁ is increased. If the viewfinder magnification ratio is increased by extending the conventional technique, It becomes necessary to reduce the value of β ₂ and the apparent field of view must be reduced.

The basic configuration of the present invention, as shown in Figure 1B, for constituting the objective lens by the positive lens component L _A at the time of high magnification is disposed on the object side and a negative lens component Lc, the conventional construction of same magnification By comparison, it is clear that the space between the eyepiece and the objective lens can be increased.

Now, as shown in the figure, the composite focal length of the positive lens component L _{A in} the high-magnification objective lens is f _A , the focal length of the negative lens component L _C is f _C , and the composite focal length of the high-magnification objective lens is f _{C. 0} , the principal point distance between the positive lens component L _A and the eyepiece lens Le is d ₃ , the principal point distance between the positive lens component L _A and the negative lens component L _C is d _4, and the image side of the high-magnification objective lens When the distance between the focal point F ₀ and the negative lens component L _C is a, and the distance between the negative lens component L _C and the principal point position (position of L _{O in} the figure) as the high-magnification objective lens is b, And arrange this, Becomes Further, from the image forming relationship for the negative lens component L _C , Is established, and if this is rearranged about f _c and the formula is substituted, Becomes Also, a _{d 3 = f e -a + d} 4.

The amount of increase in the direction of the optical axis of the eyepiece side space in the high magnification state is b = −f _O −a. Solving for a from the equations and equations, as a> 0, Becomes

From the above equations, when d ₂ , β ₁ and β ₂ are given, f ₁ , f _e , d ₁ , f _O , d ₁ -d ₂ are sequentially determined by the equation, and further d ₃ and f _c By giving, a is determined from the equation. Then, d ₄ by the formula and f by the formula
_A is the value of b calculated by the equation.

By substituting the expression for the expression, Becomes Here, by substituting the equation into the equation, a
Erase Becomes Therefore, assuming that f _o <0, f _A > 0, in order to make the space in the optical axis direction on the eyepiece side in the high magnification state larger than before, b> 0 is necessary. From the equation, it is necessary that d ₄ > 0. That is, in the condition where the right-hand side of the molecule is _{positive, i) f e -d 3 <} 0 or, _ii) at _f e -d ₃ ≧ 0, _{moreover, 4f c (f o + f} e -d 3> 0 Is the case.

<0, since it is f _e = d ₁ -f _o by _{formula, 4f c (f o + f} e -d 3) = 4f c (d 1 -d 3)> f c to be 0 , D ₁ <d ₃ . Therefore, the second condition that the numerator on the right side of the equation is positive is d ₁ <d ₃ ≦ _fe .

That is, in order to make the space in the optical axis direction on the eyepiece side in the high magnification state larger than in the conventional case, d ₁ <d ₃ may be satisfied.

Since d ₂ > d _1, it is also feasible when d ₂ = d ₃ , that is, when the high magnification state and the low magnification state have the same total length.
Further, d ₂ <because d ₃ are possible, it is also possible to convert a positive lens component L _A to a high magnification state by externally attached to the front of the viewfinder.

In the above description, the negative lens component as the first objective lens for low magnification is different from the negative lens component in the second objective lens for high magnification, but the first objective lens for low magnification is high. It can be used as a negative lens component of the second objective lens for magnification. In this case, in the above formula, it is needless to say that may be a f c ₌ f _1.

However, the first objective lens L ₁ for low magnification has a negative lens component L 1.
_In addition to _b , it has other lens components such as a positive lens component, and has a negative lens component L _{c in} the second objective lens L ₂ for high magnification.
When the negative lens component L _b in the low-magnification objective lens L ₁ is used as, the focal length of the negative lens component in the low-magnification first objective lens is f _b , and in each of the above equations, f _c = F _b . Further, other lens components in the low-magnification objective lens L ₁ can be used as they are in the high-magnification objective lens.

The above is the outline of the basic configuration disclosed in the previous application.

The present invention provides a magnification conversion type finder having such a basic structure, in the same manner as described above, the first objective lens L ₁ for low magnification.
Focal length f ₁ of the second objective lens L a positive lens component in ₂ the focal length of the positive lens component La is added to the low magnification state objective lens f _a for a high _{magnification,} the shape When the factor is Q _a , the focal length of the negative lens component Lc arranged on the eyepiece side of the second objective lens for high magnification is f _c , and the shape factor thereof is Q _c , −70 <f ₁ < _{-19 (1) -50 <f c} <-18 (2) -0.33 <f c / f a <-0.05 (3) 0.8 <Q a <8.5 (4) -1.2 <Q c <-0.8 (5) The above conditions are satisfied.

Here, the shape factor Q is the radius of curvature of the object-side lens surface and the image-side lens surface of the lens, respectively, R _O and R
When the _{I, Q = (R I +} R O) / to be defined by (R I _-R O).

The above conditions will be described below.

The condition of the expression (1) is for correcting high-order coma aberration in the low magnification state. In the reverse Galileo finder, the negative refracting power of the objective lens is stronger than the positive refracting power component of the eyepiece lens, so that aberration is likely to be remarkable in the objective lens portion. If the upper limit of this condition is exceeded, the negative refracting power as the first objective lens for low magnification becomes too strong, and divergent high-order coma aberration becomes remarkable, and particularly the image at the peripheral portion of the screen deteriorates. On the other hand, if the lower limit of this condition is not satisfied, high-order aberrations are less likely to occur, which is advantageous for aberration correction, but the overall lens length becomes too long to obtain a predetermined viewfinder magnification, thus forming a compact viewfinder. Becomes difficult.

The condition (2) is for correcting high-order coma aberration in the high magnification state. In the high magnification state, in order to reduce the space occupied by the objective lens in the optical axis direction,
It is desirable to minimize the value of a shown in FIG. 1B.
To do so, as shown in the above equation, the negative lens component
As the focal length f _c of Lc is close to 0, i.e., negative refracting power is advantageous as strong. When the negative refractive power becomes weaker than the lower limit of the condition (2), the effect of keeping the occupied space of the objective lens in the optical axis direction small becomes small for the above reason, and the basic object of the present invention cannot be achieved. If the upper limit is exceeded, it is advantageous to keep the required space of the objective lens small, but since the divergent component becomes too strong, higher-order coma aberrations occur as in condition (1). However, the deterioration of the image in the peripheral part of the visual field becomes remarkable, and it becomes difficult to obtain a good finder image.

The condition (3) is for correcting the distortion aberration in the high magnification state. The positive lens component arranged on the object side of the negative lens component forming the second objective lens for high magnification has an effect of correcting the negative distortion that tends to occur in the reverse Galileo finder. Negative lens component focal length f _c
Compared to, and the focal length f _a of the positive lens component L _a increases to be added to the high magnification ratio, if it exceeds the upper limit of this condition is weakened effect of correcting distortion due to positive lens component, a negative A large amount of distortion aberration remains. On the contrary, when the refractive power of the positive lens component becomes strong and the value goes below the lower limit of the condition (3), positive distortion occurs and it becomes difficult to perform good correction.

The condition (4) defines the shape of the positive lens component L _a added to the low magnification state in the high magnification state. First it shape factor Q _a of the positive lens component L _a is a positive value, and an object-side lens surface convex to the object side of the positive lens, and the absolute value of the radius of curvature of the eyepiece side lens surface It is larger than that of the object side lens surface. Further, it means that the bending is performed in a direction in which the radius of curvature of the object-side lens surface decreases as the value of Q _a increases. The change in Q _a has a strong effect on the correction of astigmatism, and when this value becomes small, the convergent effect of oblique rays on the lens surface of the positive lens component L _{a on} the eyepiece side becomes strong, so that the lower limit of the condition (4) is satisfied. If it deviates, astigmatism occurs and it cannot be corrected. On the other hand, if the upper limit is exceeded, the converging effect of oblique rays becomes too weak, and conversely astigmatism tends to occur, and good correction cannot be achieved.

The condition (5) defines the shape of the eyepiece-side negative lens component L _c in the second objective lens for high magnification. The fact that the value of the shape factor Q _c of this negative lens component is negative means that the lens surface on the eyepiece side is convex toward the object side, and the absolute value of the radius of curvature of the lens surface on the object side is larger than that on the lens surface on the eyepiece side. That's a big thing. Further, it means that the bending is performed in a direction in which the radius of curvature of the lens surface on the eyepiece side decreases as the value of Q _c decreases.
As described in the conditions (1) and (2), since the negative refractive power of the objective lens in the inverse Galileo finder is strong and the oblique light flux passes through the position away from the optical axis, high-order coma aberration occurs. Easy to do. Therefore, it is desirable that the object-side lens surface and the eyepiece-side lens surface share the function of diverging the oblique light beam from the viewpoint of preventing the occurrence of high-order coma aberration. If the upper limit of condition (5) is exceeded, the diverging action on the object-side lens surface will be too strong, and if it is below the lower limit, the diverging action on the eyepiece-side lens surface will be too strong. In any case, high-order coma aberration occurs, and it becomes difficult to perform good aberration correction.

(Examples) Examples according to the present invention will be described below.

The first embodiment according to the present invention is an example in which the zoom ratio is as large as 2.36 and the viewfinder magnification exceeds the unity magnification in the high magnification state. FIGS. 2A and 2B are lens configuration diagrams of the first embodiment in a low magnification state and a high magnification state, respectively. As shown,
The low-magnification objective lens L ₁ is composed of a negative lens component Lb with a convex surface facing the object side, and the high-magnification objective lens L ₂ is arranged with a positive meniscus lens component La having a convex surface facing the object side and its image side. It consists of a negative lens component Lc. Here, the negative lens component Lc in the high-magnification objective lens can also be used by moving the negative lens component Lb as the low-magnification objective lens to the eyepiece side along the optical axis. First
2A and 2B show the chief ray of maximum angle of view with a broken line,
EP represents the eye point position.

Table 1 below shows specifications of the first embodiment according to the present invention.
However, in the table, the leftmost number represents the order from the object side, and the refractive index and the Abbe number are values for the d-line (λ = 587.6 nm). Further, β ₁ represents the finder magnification in the low magnification state, β ₂ represents the finder magnification in the high magnification state, EL represents the distance from the final lens surface apex of the eyepiece to the eye point EP, and l _W and l _T are respectively It represents the total length of the lens system in the low magnification state and the high magnification state, that is, the distance from the apex of the frontmost lens surface of the objective lens to the apex of the final lens surface of the eyepiece.

Further, in each of the following examples, the aberration correction is better achieved by providing at least one aspherical surface, and this aspherical surface has an apex of the lens surface as an origin and an optical axis on the optical axis. The x-axis is the direction of travel and y is the direction perpendicular to this
When used as an axis, Shall be represented. However, C ₄ , C ₆ , C ₈ , and C ₁₀ are aspherical coefficients in each order.

Further, regarding the first example shown in Table 1, various aberrations in the low magnification state are shown in FIG. 3A, and various aberrations in the high magnification state are shown in FIG. 3B. In the aberration diagram, astigmatism is the virtual image position of an object at infinity displayed in diopter (dpt) with the eye point EP as the reference. For distortion aberration, the incident angle to the viewfinder is θ and the exit angle is θ. ′, When the viewfinder magnification is β, Shall be defined in.

The second embodiment shown in FIGS. 4A and 4B is similar to the first embodiment in the objective lens group, but the low-magnification objective lens L ₁ is composed of a single negative lens component Lb, Objective lens
L ₂ is composed of a single negative lens component Lc and a positive meniscus lens component La arranged on its object side and having a convex surface directed toward the object side. The eyepiece lens Le has a first positive lens component L _e1.
When is composed of a second positive lens component L _e2, the object-side lens surface of the first positive lens component L _e1 is formed on the transflective mirror as albada reflecting surface, of the second positive lens component L _e2 A frame F for forming an optical image frame as a field frame within the field of view of the finder is provided on the object-side lens surface.

It is necessary to make the focal length of the albada system as large as possible when putting a distance display, a strobe light emission preparation display, etc. near the optical image frame F, and generally the size of the filter must be increased because the space of the albada system in the optical axis direction is increased. Although unavoidable, according to this embodiment, a compact structure can be achieved while ensuring a sufficient space between the second objective lens for high magnification and the eyepiece. The sixth surface (final surface) in the low magnification state is formed as an aspherical surface in order to satisfactorily correct the astigmatism of the Albada system. In this example as well, the negative lens component as the first objective lens for low magnification can be used also as the negative lens component in the second objective lens for high magnification. Then, the second surface in the low magnification state and the first surface in the high magnification state
The surface is formed as an aspherical surface in order to satisfactorily correct the astigmatic difference in each magnification state.

Similar to Table 1, Table 2 below shows the specifications of the second embodiment.

Further, FIGS. 5A and 5B show various aberration diagrams in the low magnification state and the high magnification state in the second embodiment, and FIG. 5C shows the aberration diagram of the field frame image.

The third embodiment shown in FIGS. 6A and 6B is an example in which zooming is performed by a configuration substantially similar to that of the first embodiment. Then, FIG. 6C shows a configuration example in which this finder is used as a daylighting type bright frame finder. 6th C
As shown in the figure, the light flux from the frame F for the field frame arranged in parallel with the objective lens is reflected by the reflecting mirror 1 and is then placed between the objective lens L ₂ and the eyepiece lens Le. Transmission mirror 2
Is reflected by, reaches the eyepiece lens, and the virtual image of the frame F overlaps the object image as a field frame of the finder field and is observed at the same diopter.

In this embodiment, as shown in FIG. 6C, the space occupied by the semi-transmissive mirror 2 essential for daylighting is large, but it is compact as a finder. The third surface in the low magnification state is
It is formed to be an aspherical surface in order to favorably correct the aberration of the optical image frame. In this example as well, the negative lens component as the first objective lens for low magnification can be used also as the negative lens component in the second objective lens for high magnification. The second surface in the low magnification state and the second surface in the high magnification state are formed as aspherical surfaces in order to satisfactorily correct the astigmatic difference in each magnification state. Further, in the high magnification state, by using a material having a high dispersion for the positive lens component, it is possible to more satisfactorily correct the chromatic aberration of magnification.

Table 3 below shows the specifications of the third embodiment in the same manner as the above-mentioned embodiment.

Then, FIGS. 7A and 7B show various aberration diagrams of the third embodiment, and FIG. 7C shows various aberrations of the field frame image.

In all of the fourth to seventh examples described below, the positive lens component is arranged closest to the object side in the low magnification state, and this positive lens component is fixed in the conversion between the high magnification state and the low magnification state. Thus, the low magnification objective lens and the high magnification objective lens are commonly used.

FIGS. 8A and 8B are lens configuration diagrams of a fourth embodiment according to the present invention in a low magnification state and a high magnification state, respectively. The first objective lens L ₁ for low magnification is composed of a positive lens component L _1a and a negative lens component Lb fixed on the object side. The second objective lens L ₂ for high magnification has a positive lens component L _1a on the most object side which is also used in a low magnification state, and a second positive lens component La and a negative lens which are added to the low magnification state. It is composed of components Lc and. That is, a positive lens component L _A of the second objective lens L ₂ for the high magnification and two positive lenses L _1a and La. The negative lens component Lc in the high magnification state can also be used by moving the negative lens component Lb in the low magnification state along the optical axis.

The fourth surface in the low magnification state and the sixth surface in the high magnification state (both surfaces on the eyepiece side of the negative lens component) are formed as aspherical surfaces in order to better correct the astigmatic difference in each state. Has been done.

The specifications of the fourth embodiment as described above are similar to those of the above embodiment,
The results are shown in Table 4 below. Further, various aberration diagrams in the low magnification state and the high magnification state are shown in FIGS. 9A and 9B, respectively.

FIGS. 10A and 10B are lens configuration diagrams of the fifth embodiment in a low magnification state and a high magnification state. In this embodiment, the first objective lens L ₁ for low magnification and the second objective lens L ₂ for high magnification are used.
The configuration of is similar to that of the fourth embodiment. Further, the eyepiece lens Le has the same structure as that of the second embodiment.
It consists of two positive lens components and is configured as an albada-type bright frame finder. That is, in the low magnification state, the optical image frame F is provided on the seventh surface and the fifth surface is a semi-transmissive mirror surface, and this albada system is commonly used in the low magnification state and the high magnification state. The eighth surface (final surface) in the low magnification state is formed as an aspherical surface in order to better correct the astigmatism of the Albada optical system. Further, the negative lens component in the first objective lens L ₁ for low magnification is
It can also be used as a negative lens component in the second objective lens L ₂ for high magnification. The fourth surface in the low magnification state and the sixth surface in the high magnification state (both surfaces on the eyepiece side of the negative lens component) are formed as aspherical surfaces in order to better correct the astigmatic difference in each state. Has been done.

Aberration diagrams of the fifth embodiment in the low-power state and the high-power state are shown in FIGS. 11A and 11B, respectively. Fig. 11C shows various aberration diagrams for the field frame image in the Albada optical system.
Shown in the figure.

The sixth embodiment shown in FIGS. 12A and 12B is an example in which zooming is performed by a configuration substantially similar to that of the fifth embodiment. Then, FIG. 12C shows an example in which this finder is configured as a daylighting type bright frame finder similar to the third embodiment shown in FIG. 6C. As shown in FIG. 12C, the luminous flux from the frame F for the field frame arranged in parallel with the objective lens is reflected by the reflecting mirror 1 and then arranged between the objective lens L ₂ and the eyepiece lens Le. The image is reflected by the semi-transmissive mirror 2, reaches the eyepiece lens, and the virtual image of the frame F overlaps the object image as a field frame of the finder field and is observed at the same diopter.

Also in this embodiment, the negative lens component Lb in the first objective lens L _{1 is}
Can also be used as the negative lens component Lc in the second objective lens. As shown in FIG. 12C, the semi-transparent mirror 2, which is essential for daylighting, occupies a large space, but it is compact as a finder. The fourth surface in the low-magnification state and the sixth surface in the high-magnification state (both surfaces on the eyepiece side of the negative lens component) are formed as aspherical surfaces in order to satisfactorily correct the astigmatic difference in each state. .

The specifications of the sixth embodiment as described above are shown in Table 6 below.

Further, FIGS. 13A and 13B show various aberration diagrams of the sixth embodiment, and FIG. 13C shows various aberrations of the field frame image.

The seventh embodiment has the same low-magnification state as the sixth embodiment, and upon conversion to a high-magnification state, as shown in FIG. 14, a positive meniscus lens having a convex surface facing the object side of the finder, as shown in FIG. The component La is added. Then, at this time, the negative lens component Lb in the first objective lens for low magnification moves to the eyepiece side. When a positive lens is added to convert to a high-magnification state as in this embodiment, the limitation for reducing the total length of the finder system is mainly the low-magnification state, and there are not many restrictions in the high-magnification state. .

Table 7 shows the specifications of the seventh embodiment. Further, FIG. 15 shows various aberration diagrams of this example in the high magnification state. The aberration diagrams at the low magnification state are the same as FIG. 13A.

In each of the above embodiments, in order to adapt the length of the finder to the thickness of the camera body, it is desirable that the total length l _w of the finder optical system in the low magnification state is set to 20 <l _w <47. . Further, in the high magnification state, the positive lens component added to the object side is advantageous in increasing the space on the eyepiece side as the distance from the negative lens component on the eyepiece side increases. The ratio l _T / l _W between the state and the low magnification state is preferably 0.8 or more.

In any of the above examples, it is possible to use the negative lens component in the first objective lens for low magnification as the negative lens component in the second objective lens for high magnification. In this case, the degree of freedom of aberration correction in each magnification state decreases, and when not used in common, the optimum negative lens component can be configured for each magnification, and therefore the degree of freedom in design is high. Incidentally, in general, a fixed window of a plane parallel plate is often provided on the object side or the eyepiece side of the finder, but since the finder is an afocal system, there is almost no change in aberration. Does not mention these. It goes without saying that a parallel plane plate window may be provided if necessary.

(Effect of the Invention) As described above, according to the present invention, it is possible to realize a reverse Galilean viewfinder in which a large space for the eyepiece lens necessary for switching magnification is secured, and which is compact and in which various aberrations are well corrected in each magnification state. It is possible to Therefore, various kinds of information can be clearly displayed within the field of view of the finder, and it is possible to provide a finder that is compact and has a clear field of view.

[Brief description of drawings]

FIG. 1 is a principle explanatory view of an optical system showing a configuration of magnification conversion which is a basis of the present invention, FIGS. 2A and 2B are lens configuration diagrams in a low magnification state and a high magnification state of the first embodiment, FIGS. 3A and 3B are aberration diagrams in the low magnification state and high magnification state of the first embodiment, and FIGS. 4A and 4B are lens configuration diagrams in the low magnification state and the high magnification state of the second embodiment. FIGS. 5A and 5B are aberration diagrams of the second embodiment in a low magnification state and a high magnification state, FIG. 5C is a diagram of aberrations of the field frame of the albada system in the second embodiment, FIGS. 6A and 6B. The figure is the third
FIG. 6C is a configuration diagram of a lens in a low magnification state and a high magnification state of the embodiment, FIG. 6C is a configuration diagram of a third embodiment with a daylighting type, and FIGS. 7A and 7B are low magnification states and a high magnification state of the third embodiment. FIG. 7C is a diagram of various aberrations in the state, FIG. 7C is a diagram of various aberrations regarding the field frame by the daylighting frame type in the third example, and FIGS. 8A and 8B are lens configurations in the low magnification state and the high magnification state of the fourth example. FIGS. 9A and 9B are aberration diagrams in the low magnification state and the high magnification state of the fourth embodiment, and FIGS. 10A and 10B are lens configurations in the low magnification state and the high magnification state of the fifth embodiment. FIGS. 11A and 11B are aberration diagrams of the fifth embodiment in the low magnification state and the high magnification state, and FIG. 11C is a diagram of various aberrations of the field frame of the albada system in the fifth embodiment.
FIGS. 12A and 12B are lens configuration diagrams of a sixth embodiment in a low magnification state and a high magnification state, FIG. 12C is a configuration diagram of the sixth embodiment with a daylighting type, and FIGS. 13A and 13B are sixth configuration drawings. FIG. 13C is a diagram showing various types of aberration in the low-power state and high-power state of Example, FIG. 13C is a diagram of various types of aberration relating to the field frame of the daylighting frame type in Example 6, and FIG. 14 is a lens in the high-power state of Example 7 FIG. 15 is a diagram of various types of aberration in a high magnification state of the seventh embodiment. [Explanation of Signs of Main Parts] L ₁ ...... Lower magnification first objective lens L ₂ ...... High magnification second objective lens Lb ...... Negative lens component L _A ...... constituting first objective lens ...... 2 Positive lens component La that composes the objective lens ..... Positive lens component in the second objective lens that is added to the low magnification state Lc ..... Negative lens component Le that composes the second objective lens. Eyepiece

Continuation of the front page (56) Reference JP-A-52-62023 (JP, A) JP-A-60-57329 (JP, A) JP-A-59-23330 (JP, A) JP-A-53-63014 (JP , A) JP 56-101132 (JP, A) JP 57-624 (JP, A) JP 50-87027 (JP, A) Actually open 59-168738 (JP, U) Actually open 60-8935 (JP, U) JP 37-484 (JP, B1) JP 41-10754 (JP, B1)

Claims (1)

[Claims] 1. An objective lens group having a negative refracting power and an eyepiece lens Le having a positive refracting power arranged at a predetermined distance from the objective lens group, in order from the object side, the objective lens group being a negative lens. a first objective lens L ₁ for low magnification with component Lb, second for high magnification and a positive lens component La is added to arranged the first objective lens on the object side and a negative lens component Lc The second objective lens L ₂ and the high magnification second
Synthesis negative refractive power of the objective lens L ₂ is smaller than the negative refractive power of the first objective lens L ₁ for the low magnification, the low magnification first objective lens L ₁ is the eyepiece Le and the same optical axis for In the reverse Galileo finder, which is selectively configured to have a low magnification state to be arranged and a high magnification state in which the second objective lens for high magnification is arranged on the same optical axis as the eyepiece lens Le, the first focal length f ₁ of the objective lens L _1, the second objective lens positive lens is added to the first objective lens of a positive lens component in L ₂ for the low magnification for the high magnification focal length f _a of the component La _(the unit mm), the focal length of the negative lens component Lc of the eyepiece side in the second objective lens is f _{c (unit} mm), a second objective for the high magnification A positive lens component in the lens is a positive lens component added to the first objective lens for low magnification. When lens component La of the shape factor _{Q a} of the shape factor of the eyepiece side negative lens component Lc in the second objective lens and _{Q c, -70 <f 1 <} -19 (1) -50 <f c <-18 (2) -0.33 <and characterized by satisfying the conditions of _{f c / f a <-0.05 (} 3) 0.8 <Q a <8.5 (4) -1.2 <Q c <-0.8 (5) Magnification conversion type reverse Galileo finder. However, the shape factor Q of the lens is the radius of curvature of the object-side lens surface and the image-side lens surface of the lens, respectively.
When R _O and R _I are defined, Q = (R _I + R _O ) / (R _I −R _O ).