JPH0638142B2 - Inverted galileo finder with conversion ratio - Google Patents

Description

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 magnification conversion.

(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 field of view in the shooting range constant and 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 negative lens L2 is replaced with a negative lens L1 having a different focal length, or as shown in FIGS. 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 high at high magnification and at low magnification. It has a drawback that it is large, and therefore 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 on the optical axis for magnification conversion is large, the space for arranging the optical members for displaying various information becomes small,
As the design constraints became larger, it became difficult to display sufficient information.

(Object of the Invention) The object of the present invention is to solve the above-mentioned conventional drawbacks, and to reduce the amount of displacement of the lens in the optical axis direction due to the magnification conversion of the inverse Galileo finder, thereby making it more advantageous to form a compact finder. Therefore, it is an object of the present invention to provide a reverse Galileo finder capable of magnification conversion and capable of displaying a large amount of information within the field of view of the finder.

(Outline of the Invention) As shown in FIGS. 3 (A) and 3 (B), the inverse Galileo finder capable of changing the magnification in accordance with the present invention allows a part or all of the negative lens Lb as the objective lens in the low magnification state to be brought into the eyepiece. The high-magnification state is achieved by moving to the side and inserting the positive lens La into these object sides. 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 distance from the lens group Lb are provided. By moving at least one negative lens in the lens Lb to the eyepiece side, by inserting the positive lens La on the optical axis on the object side of the moved negative lens Lb, to a higher magnification. It enables conversion. Therefore, in the high magnification state, the composite system of the positive lens La and the negative lens Lb substantially constitutes the objective lens Lo.

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 objective lens Lo in the general high magnification state shown in FIG. 4 is substantially constituted by the composite system of the positive lens La and the negative lens Lb. In the high magnification state shown in FIG. 6, in order to simplify the explanation, the negative lens Lb as the objective lens in the low magnification state shown in FIG. 5 is integrally moved to the eyepiece side. .

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

Next, in FIG. 5, the viewfinder magnification on the low magnification side (wide angle side) is β2, the focal length of the objective lens Lb is fb, the focal length of the eyepiece lens Le is fe, as in the high magnification side, the objective lens Lb and the eyepiece lens Le. Let d2 be the distance between the principal points of β2 = -fb / fe (3) However, β1> β2 d2 = fe + fb (4) Solving equations (3) and (4) gives 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. The value of fo is obtained by substituting equation (6) into equation (1). Is required.

The amount of displacement in the optical axis direction between the negative lens Lo as a general high-power objective lens and the negative lens Lb as a low-power objective lens 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 is 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 when the negative lenses L1 and L4 forming the objective lens in the low magnification state are close to each other. ≒ d2
-D1. 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 variable magnification method, the demand for further reduction of the value of β2 increases, and the apparent field of view must be reduced. Absent.

The present invention reduces the amount of displacement of the negative lens in the optical axis direction while maintaining the same magnification β2 by the arrangement of FIG. 6 instead 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 Lb forming the objective lens are fa and fb, respectively, and these positive lens La and negative lens Lb 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, move the negative lens Lb to the eyepiece Le side and move the positive lens La
It may be inserted on the optical axis of the negative lens Lb on the object side with a principal point distance d4. Therefore, comparing the conventional high-magnification state of FIG. 4 with the high-magnification state of the present invention of FIG. 6, the negative lens in the optical axis direction for converting to the geometrically same high-magnification condition. It is clear that the amount of displacement decreases.

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 Lb is a, Organize this, Also, from the image formation relationship for the negative lens Lb, Rearranging the above equation for fb 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, the magnification β2 in the low magnification state, the addition of the positive lens and the eyepiece lens in the high magnification state Given the spacing d3,
From equations (5) to (9), fb, fe, d1 fo, d2-d1
Are sequentially determined, and a is determined by the equation (14). Further, the value of fa is determined by the equation (10), and the value of b is determined by the equation (13). And negative lens Lb for zooming
The displacement amount Δ in the optical axis direction required by is calculated as Δ = a− | fb |.

Then, by substituting the equation (14) into the equation (12), the principal point distance d4 between the positive lens La and the negative lens Lb is Is required.

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

Here, assuming that fo <0, fa> 0, 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 related art. To do so, d4>
Must be 0. That is, in the equation (15), the numerator on the right side needs to be positive. (1
The condition for the numerator on the right side of the equation (5) to be positive is (i) fe-d3 <0 or (ii) fe-d3 ≧ 0 and 4fb (fo + fe-d3)> 0.

Since fb <0 and fo + fe = d1 according to the formula (2), it is necessary that d1 <d3 in order to satisfy 4fb (fo + fe−d3) = 4fb (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, it is possible to convert to a high magnification by mounting the positive lens La externally on the front of the viewfinder instead of being built in near the viewfinder as shown in FIG. 3 (A). Is. Further, according to the method of the present invention, β1 ≧ 1 on the high magnification side, that is, it is possible to perform the same magnification or enlargement. Further, in the present invention, since a positive lens is inserted as an objective lens in a high magnification state, it is also advantageous for correcting negative distortion aberration which tends to occur in an inverse Galileo finder.

In the above description, the finder system is described as a completely afocal optical arrangement. However, in an actual finder, a perfect afocal system is not formed, 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, lens shape, 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 amount of displacement of the negative lens for zooming becomes smaller than that in the conventional case. Further, when the number of objective lenses in the low magnification state is two or more, the negative lens displacement amount can be reduced according to the principle of the present invention by moving a part of the negative lenses and adding a positive lens. It is clear that there is. Incidentally, in the viewfinder of a camera, various optical members such as a semi-transparent mirror for making a light image frame lighting type and a lens having a semi-transparent mirror surface for making an Arbata finder are often added on the optical axis. However, 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 According to the equation (14), a = 37.346 (15), d4 = 8.179 (10), fa = 90.268 (2), d1 = 23.100 (13), b = 3.721 In this case, by moving the negative lens by Δ = 11.679, an inverse Galileo finder capable of switching the magnification to a high magnification is constructed while reducing the displacement of the negative lens by 3.721 as compared with the conventional variable 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, from equation (14) a = 36.497 from equation (15) d4 = 10.830 from equation (10) fa = 97.321 from equation (2) d1 = 23.100 from equation (13) b = 4.570 In this case, by moving the negative lens by Δ = 10.83, an inverse Galileo finder capable of switching the magnification to high magnification is constructed while reducing the displacement of the negative lens by 4.570 as compared with the conventional variable magnification. Thus, even if d2 = d3, a magnification conversion finder can be realized as in the previous example. If the total length on the low magnification side is the total viewfinder length, d3
It is desired that ≦ d2, but according to the equation (14), the larger the value of d3, the smaller the value of a. Therefore, (13)
Since the value of b increases according to the formula, 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.

Third embodiment d2 = d3 = 40, β2 = 0.5X, (β1 / β2) = 2.2 From formula (5), fb = −40.0 From formula (6), fe = 80.0, β1 = 1.1 From formula (1) , Fo = −88.0 From the equation (14), a = 68.166 (15), d4 = 28.166 (10), fa = 124.968 (2), d1 = −8.0 (13), b = 19.834 In this case, by moving the negative lens by Δ = 28.166, an inverse Galileo finder capable of switching the magnification to high magnification is constructed while reducing the displacement of the negative lens by 19.834 compared to the conventional zooming. In this example as well, d2 = d3, but β1 has a considerably high magnification, and the magnification ratio (β1 / β2) = 2.2 is large, so that magnifying observation is possible at a high magnification of β1 = 1.1. It should be noted that d1 = −8.0 means that in the high magnification state of the conventional method, a negative lens with a focal length fo = −88.0 should be arranged further on the observation side of the eyepiece lens, that is, a Galileo telephoto system should be provided. I mean. Therefore, according to the present invention, telescopic observation is also possible by fixing the eyepiece lens and displacing and adding the lens on the object side.

(Effects of the Invention) As described above, as is clear from specific numerical examples, according to the present invention, the displacement amount of the negative lens in the optical axis direction is considerably smaller than that of the conventional method, but it is compact. A reverse Galileo finder with a structure that allows easy switching of magnification 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 symbols of main parts] Lo ... Objective lens, Lb ... Negative lens La ... Positive lens, Le ... Eyepiece 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. And moving at least one negative lens in the negative lens group to the eyepiece side, and inserting a positive lens on the optical axis closer to the object side than the moved negative lens to obtain a higher magnification. Inverted Galileo finder that can be converted to