JPH0638143B2 - Inverted galileo finder with conversion ratio - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a finder used in a camera or the like, and more particularly to a reverse Galilean finder capable of converting a magnification.

(Background of the Invention) In a focal length switchable camera, it is desired that the shooting range display be switched in the finder as the angle of view of the shooting lens is changed. In a camera incorporating a reverse Galileo finder, a method of changing the size of the field frame and a method of changing the magnification of the finder are conventionally known as means for switching the display of the photographing range. As a method of changing the size of the field frame, for example, a method of illuminating an optical image frame and moving the optical image frame to change the apparent size of the frame is known. It has the disadvantage that the apparent field of view of the field frame is reduced, making it less powerful and hard to see. On the other hand, with the method of changing the magnification of the viewfinder, it is possible to make the apparent visual field of the shooting range constant, and it is possible to observe with a feeling closer to the actual shooting screen, and to change the size of the field frame It has better characteristics than

As a method of converting the magnification, the focal length of the negative lens as the objective lens may be changed and the afocal state may be maintained between the objective lens and the eyepiece having the positive refractive power. Specifically, as shown in FIGS. 1 (A) and (B), the lens L2 is often replaced with a negative lens L1 having a different focal length, or as shown in FIGS. 2 (A) and (B), A conventionally known method is to remove the lens L4 from the optical path and move the negative lens L1 to the observation side to perform conversion to a high magnification. In each drawing, (A) shows the low magnification state, that is, the wide-angle side, and (B) shows the high magnification state, that is, the telephoto side. Although these methods described above are magnification conversion methods by inserting and removing the negative lens on the optical axis, in this method, the amount of displacement of the negative lens in the optical axis direction is different between the optical magnification and the low magnification. It is large and it is difficult to secure a sufficient space on the side of the eyepiece, and for this reason, there is a drawback that the structure of the finder tends to be large. In the finder for a camera, it is desirable to set the total length of the finder to be equal to or shorter than the thickness of the body of the camera. In practice, the total length of the finder is desired to be about 30 mm to 40 mm. In particular, with recent viewfinders, it is desired to simultaneously display a large amount of information such as the field of view frame, the range-finding frame, the shooting distance display, and the appropriateness of the exposure amount within the field of view. It has become necessary to add a member that requires a space, such as a semi-transparent mirror for daylighting. However, when the amount of displacement of the negative lens for converting the magnification on the optical axis is large, the space for arranging the optical members for displaying various types of information becomes small and the design constraint becomes large and sufficient. Information display was difficult.

(Object of the Invention) The object of the present invention is to solve the above-mentioned conventional drawbacks and to reduce the amount of reduction of the eyepiece side space in the viewfinder due to the magnification conversion of the inverse Galileo viewfinder, and thus the effective space in the viewfinder. It is an object of the present invention to provide a reverse Galileo finder capable of magnification conversion, which makes it possible to form a compact finder more effectively while ensuring a large number of pixels and thereby display a large amount of information in the finder field.

(Outline of the Invention) As shown in FIGS. 3 (A) and 3 (B), the reverse Galileo finder capable of converting the magnification according to the present invention has a negative lens Lb as an objective lens in a low magnification state and a positive lens in order from the object side. A high-magnification objective lens Lo having La and a negative lens Lc is exchangeably provided, and a high-magnification state is achieved by replacing the negative lens Lb with the high-magnification objective lens Lo. That is, in order from the object side, a lens group Lb having a negative refracting power as an objective lens, and a lens group Le having a positive refracting power as an eyepiece arranged at a predetermined interval from this are provided, and further, High magnification objective lens Lo that can replace the negative lens group Lb as the low magnification objective lens
Is composed of a positive lens La and a negative lens Lc in order from the object side, and by exchanging the negative lens Lb and the high-magnification objective lens, conversion to a high-magnification state is possible.

Hereinafter, the geometrical optical basic structure of the inverse Galileo finder capable of converting the magnification according to the present invention will be described in detail.

FIG. 4 is a geometrical optical configuration diagram showing a conventional general high magnification state, FIG. 5 is a geometrical optical configuration diagram showing a low magnification state of an inverse Galileo finder according to the present invention, and FIG. 3 is a geometrical optical configuration diagram of the reverse Galileo finder according to FIG. In the reverse Galileo finder capable of converting the magnification of the present invention, the state of FIG. 5 is the low magnification state and the state of FIG. 6 is the high magnification state. In the high magnification state of the present invention, the high magnification objective lens Lo is formed by a composite system of the positive lens La and the negative lens Lc, and substantially in the general high magnification state shown in FIG. It has the same function as the objective lens Lo.

Now, the general high magnification state in FIG. 4 (that is, the telephoto side)
The viewfinder magnification of β1, the focal length of the objective lens Lo
If fo is the focal length of the eyepiece lens and fe is the distance between the principal points of the objective lens Lo and the eyepiece lens Le, and the viewfinder is assumed to be a perfect afocal system, then β1 = -fo / fe (1) d1 = fe + fo (2) holds.

Next, in FIG. 5, the finder magnification on the low magnification side (wide angle side) is β2, the focal length of the negative lens Lb as the objective lens is fb, and the focal length of the eyepiece lens Le is the same as f on the high magnification side.
e, If the distance between the principal points of the objective lens Lb and the eyepiece lens Le is d2, β2 = −fb / fe (3) where β1> β2 d2 = fe + fb (4) Solving equations (3) and (4) , Here, as a comparison with the prior art shown in FIG. 1, the negative lens L1 as the objective lens in the high magnification state is compared.
Is the focal length fo, the negative lens L2 as the objective lens in the low magnification state has the focal length fb, and the positive lens L3 as the eyepiece has the focal length fe.
The displacement amount of the negative lens L2 and the negative lens L1 for magnification conversion is s1.

In such an example according to the related art, when the distance between the objective lens and the eyepiece lens in the high magnification state and the low magnification state is d1 and d2, respectively, d2> d1, and therefore the total finder length is defined by the value of d2. The dimension is usually close to the thickness of the camera body. The value of d1 is (1) in equation (2),
By substituting equation (6), Is required. For the value of the focal length fo of the objective lens Lo for high magnification, the formula (6) is substituted into the formula (1), Is required.

The amount of displacement of the negative lens Lo as a general high-power objective lens and the negative lens Lb as a low-power objective lens in the optical axis direction is approximately d2-d1 if the position of the eyepiece fe is fixed.
Indicated by the amount of. From equation (7), Becomes

Given d2 and β1, β2 as the conditions of the finder, according to equations (5), (6), (7), (8), and (9),
Lens arrangements in a low magnification state and a high magnification state are defined.

Therefore, the negative lens L1 according to the conventional method shown in FIGS.
The amount of displacement s1 with respect to L2 needs to be roughly the same as in equation (9).
In the prior art of FIG. 1, the displacement amount s1 = d2-d1, and in the prior art of FIG. 2, the displacement amount s2≈d2-d1 when the lenses L1 and L4 are close to each other.

By transforming the equation (9), If the magnification ratio β1 / β2 of the finder is set to a constant value, (β1 / β2)> 1,0 <β2 <1. Therefore, the smaller the value of β2, the smaller d2-d1. .

On the other hand, if the value of d2-d1 is restricted to a certain value or less, the upper limit of β2 is defined, and conventionally, only a viewfinder with a small value of β2 and thus a small visual field was provided. Formula (9 ') is the viewfinder magnification ratio β1
The larger the value of / β2, the more negative lens displacement d2-
It also means that d1 increases, and if the finder magnification ratio β1 / β2 is increased by the conventional magnification method, the demand for further decreasing the value of β2 increases, and the apparent field of view must be reduced. .

The present invention can secure a large effective space in the finder while maintaining the same magnification β2 by the arrangement of FIG. 6 regardless of the conventional arrangement shown in FIG. 4 on the high magnification side.

In the high magnification state of FIG. 6, the focal lengths of the positive lens La and the negative lens Lc forming the objective lens are fa and fc, respectively, and the positive lens La and the negative lens Lc are arranged at the principal point distance d4. The combined focal length of the objective lens is fo
And the distance between the principal points of the positive lens La and the eyepiece lens fe is d3. To switch from low magnification to high magnification, remove the negative lens Lb as the objective lens for low magnification from the optical path, and instead use the positive lens La and the negative lens Lc provided with the principal point interval d4 therebetween for high magnification. Insert the objective lens Lo into the optical path. Here, comparing the conventional high-magnification state of FIG. 4 with the high-magnification state of the present invention of FIG. 6, the space on the eyepiece side of the negative lens for converting into the same geometrically high magnification condition. It is clear that d5 is increased over d1.

In the high magnification configuration according to the present invention shown in FIG. 6, when the distance between the object side focus fe of the eyepiece lens Le and the negative lens Lc is a, Organize this, Further, from the image formation relationship for the negative lens Lc, By rearranging the above equation for fc and substituting equation (10), Is required. And d3 = fe-a + d4 (12).

The difference in the displacement amount of the negative lens according to the prior art and the present invention, that is, the position of the negative lens Lo in the high magnification state according to the conventional variable magnification system shown in FIG. 4, and the variable magnification system according to the present invention shown in FIG. The distance b to the position of the negative lens Lo in the high magnification state by is expressed by b = -fo-a (13).

Solving for a from Eqs. (11) and (12), a>
Because 0 According to the above formula, in addition to the distance d2 between the objective lens and the eyepiece lens in the low magnification state, the magnification β1 in the high magnification state, and the magnification β2 in the low magnification state, the addition of the positive lens and the eyepiece lens in the high magnification state The magnification given the interval d3 is
From equations (5) to (9), fb, fe, d1 fo, and d2-d1 are sequentially determined, and for an arbitrary negative value fc, a is determined by equation (14). Furthermore, according to equation (10), fa becomes (1
The value of b is determined by the equation 3). And
The reduction amount Δ of the eyepiece side space in the finder due to the exchange of the objective lens for zooming is determined as Δ = a− | fb |.

Then, by substituting the equation (14) into the equation (12), the axial distance d4 between the positive lens La and the negative lens Lc becomes Is required.

By substituting the equation (13) into the equation (10), Becomes

Here, assuming that fo <0, fa> 0, the decrease amount Δ of the space on the eyepiece side of the negative lens Lc according to the present invention is smaller than the displacement amount of the negative lens according to the related art. It suffices if it is 0. For that purpose, d4>
Must be 0. That is, in the equation (15), the numerator on the right side needs to be positive. (1
The condition that the numerator on the right side of the equation (5) is positive is (i) fe-d3 <0 or (ii) fe-d3 ≧ 0 and 4fc (fo + fe-d3)> 0.

Since fc <0 and fo + fe = d1 according to the equation (2), d1 <d3 is required to be 4fc (fo + fe−d3) = 4fc (d1−d3)> 0. .

That is, since the displacement amount of the negative lens Lb according to the present invention is smaller than the displacement amount of the negative lens according to the conventional technique, d1
<D3 is fine.

In general, since d2> d1 also holds, when d2 = d3, that is, when the total length of the viewfinder in the high-magnification state and the low-magnification state is the same, it can be realized. Since d2 <d3 is also possible, the positive lens La is not disposed at the same axial position as the negative lens Lb as shown in FIG.
It is also possible to convert to high magnification by providing La on the front of the finder. Further, according to the method of the present invention, β1 ≧ 1 on the high magnification side, that is, it is also possible to achieve equal magnification or enlargement. Further, in the present invention, since a positive lens is provided as an objective lens in a high magnification state, it is also advantageous for correcting negative distortion aberration that tends to occur in an inverse Galileo finder.

In the above description, the finder system is described as a completely afocal optical arrangement, but in an actual finder, the finder system may not be a perfect afocal system and a predetermined diopter correction may be added. It goes without saying that this diopter correction is easily achieved by moving the eyepiece lens Le toward the object side or the observation side by an amount corresponding to a predetermined diopter.

The geometrical optical basic configuration of the present invention has been described above in detail,
Since the position of the principal point of the eyepiece lens or the objective lens can be changed depending on the specific lens configuration, the lens shape, the lens thickness, etc., the values of d1, d2, and d3 described above do not always match the total length of the finder. However, according to the above-described principle of the present invention, it is clear that the reduction amount of the space on the eyepiece side in the finder becomes smaller when the magnification is converted to a higher magnification than the conventional one. Incidentally, in the viewfinder of a camera, various optical members such as a semi-transparent mirror for adopting a light image frame lighting type and a lens having a semi-transparent mirror surface for an alvada finder are often added on the optical axis. , These members can be considered in addition to a part of the objective lens or the eyepiece lens.

(Example) Next, specific numerical values will be illustrated as examples according to the present invention.

First embodiment d2 = 38.5, d3 = 35, β2 = 0.4X (β1 / β2) = 1.6 From the formula (5), fb = −25.667 From the formula (6), fe = 64.167 β1 = 0.64 From the formula (1) , Fo = −41.067 fc = −30.0 By the formula (14), by a = 38.451 (15), by d4 = 9.284 (10), by fa = 145.744 (2), and d1 = 23.100 (13) , B = 2.616 In this case, Δ = 12.7 in the high magnification state as compared to the low magnification state.
Although the eyepiece lens side space is reduced by 84, it is possible to enlarge the eyepiece lens side space in the viewfinder by 2.616 compared to the conventional variable magnification and switch the magnification to a higher magnification.

Second embodiment d2 = d3 = 38.5 β2 = 0.4X, (β1 / β2) = 1.6 Formula (5) fb = −25.667 Formula (6) fe = 64.167, β1 = 0.64 Formula (1) fo = −41.067, fc = fb = −25.667 Equation (14), a = 36.497 Equation (15), d4 = 10.830 Equation (10), fa = 97.321 Equation (2) d1 = 23.100 (13) From the formula, b = 4.570 In this case, Δ = 10.8 in the high-magnification state compared to the low-magnification state.
Although the space on the side of the eyepiece decreases by 30, the space on the side of the eyepiece in the viewfinder can be enlarged by 4.57 compared with the conventional variable magnification, and it is possible to switch to a higher magnification. Thus, even if d2 = d3, a magnification conversion finder can be realized as in the previous example. If the total length of the low magnification side is taken as the total length of the finder, it is desired that d3 ≤ d2, but the larger the value of d3 in Eq. (14), the smaller the value of a. Since the value becomes large, when d2 = d3, that is, in the high magnification state, if the positive lens is arranged at the same position as the objective lens in the low magnification state, the viewfinder becomes the most compact. Further, in this embodiment, the negative lens Lb as the low magnification objective lens and the negative lens constituting the high magnification objective lens are used.
Since the focal lengths are the same as Lc, it is advantageous that they can be manufactured as a common lens.

Third Embodiment d2 = d3 = 40, β2 = 0.5X, (β1 / β2) = 2.2 From the formula (5), fb = −40.0 From the formula (6), fe = 80.0, β1 = 1.1 From the formula (1) , Fo = -88.0 fc = -30.0 Formula (14), a = 62.895 (15) Formula, d4 = 22.895 (10) Formula, fa = 80.253 (2) Formula, d1 = -8.0 (13) Formula As a result, b = 25.105 In this example as well, d2 = d3, but β1 is a very high magnification, and the magnification ratio is as large as 2.2, which is an example in which magnified observation is possible in a high magnification state of β1 = 1.1. In addition, d1 = -8.0
This means that in the high magnification state of the conventional system, a negative lens having a focal length fo = -88.0 is arranged further on the observation side of the eyepiece lens, that is, a Galileo type telephoto optical system. Therefore, according to the present invention, it is possible to perform telescopic observation simply by exchanging the lens on the object side of the eyepiece lens.

(Effects of the Invention) As described above, as is clear from specific numerical examples, according to the present invention, the size of the eyepiece lens side in the viewfinder is kept larger than that of the conventional one during zooming, yet it is compact and simple. A reverse Galilean viewfinder with a magnification changeable structure is realized. Therefore, it is possible to secure a sufficient space for accommodating optical members for performing various displays within the field of view of the finder, and it is possible to provide a magnification conversion type reverse Galileo finder capable of displaying a large number of information. .

[Brief description of drawings]

FIGS. 1 (A) and (B) and FIGS. 2 (A) and (B) are optical path diagrams showing a variable magnification system of an inverse Galileo finder according to the prior art. (A) of each figure shows a low magnification state, 3B shows a high magnification state, and FIGS. 3A and 3B are basic configuration diagrams showing the magnification switching operation of the reverse Galileo finder according to the present invention. FIG. 3A shows a low magnification state, and FIG. FIG. 4, FIG. 5, and FIG. 6 are views for explaining the geometrical optical basic structure of the present invention, and FIG. 4 shows a high-magnification state in the conventional method. 5 and 6 show a low magnification state and a high magnification state according to the present invention, respectively. [Description of Signs of Main Parts] Lb ... Negative lens, Le ... Eyepiece lens La ... Positive lens Lc ... Negative lens, Lo ... Objective lens

Claims (1)

[Claims] 1. A lens group having a negative refracting power as an objective lens and a lens group having a positive refracting power as an eyepiece arranged at a predetermined distance from the negative lens group in order from the object side. In the reverse Galileo finder that we have,
Inverse Galileo finder capable of magnification conversion by exchanging the negative lens group as the objective lens with another objective lens having a positive lens and a negative lens in order from the object side.