JPH055839A - Finder optical system - Google Patents

Abstract

PURPOSE:To provide a variable power finder optical system where eclipse of a finder image accompanied with power variation of the finder optical system is prevented regardless of the change of a photographic lens. CONSTITUTION:A finder optical system has the power varying function and is provided with a focusing screen 8 and satisfies conditions -(EZX0.0107-0.01)<=(FW+BW)/FW<2> and -(FT+BT)FT<2=(EZX0.0107-0.01) where EZ, FW, BW, FT, and BT are a ratio of the maximum value to the minimum value of the absolute value of the power of the finder optical system, the distance from the image surface of the photographic lens to the front principal point position of the finder optical system in the state that the absolute value of the power of the finder optical system is minimum, the distance from the pupil position of the finder optical system to the rear principal point position of this optical system in the same state, the distance from the image surface of the photographic lens to the front principal point position of the finder optical system in the state that the absolute value of the power of the finder optical system is maximum, and the distance from the pupil position of the finder optical system to the rear principal point position of this optical system in the same state respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system, and more particularly to a finder optical system used in a trimmable single-lens reflex camera.

[0002]

2. Description of the Related Art Recently, a trimming system has been proposed for a camera.
By printing a predetermined range within the image forming area B of the film 5 shown in (a), that is, information for specifying a part of the area A on a predetermined portion 51 of the emulsion surface of the film 5, at the time of printing. In this system, the area A is stretched so that it can be printed on the area A ′ of the photographic printing paper 52 shown in FIG. Specifically, the trimming information is recorded in the predetermined portion 51 of the film 5 in the trimming mode shooting, this information is read by the reading device at the time of printing, and the enlargement zooming is performed by the printing device according to the information. It is done. Enlargement zooming by this trimming information is performed by "electronic zoom" or "pseudo zoom".
The ratio of the diagonal length of the area specified by the electronic zoom to the diagonal length of the film is the trimming magnification (E
Z).

By the way, it is difficult to take an image of a subject viewed through the viewfinder optical system during trimming unless it is known which part is to be trimmed. In order to solve this, it has been proposed that the viewfinder optical system be pseudo-zoomed by an amount corresponding to the trimming magnification so that the viewable field frame of the viewfinder corresponds to the trimmed portion.

[0004]

However, when the viewfinder optical system is configured to be variable in magnification, a problem occurs when a part of the viewfinder optical system is moved.
This means that the viewfinder image may be vignetting depending on the exit pupil of the taking lens attached to the camera body.

That is, the taking lens is replaceable, and various focal lengths and FNOs (ef number) are attached. Since these have different exit pupils and the directions of the lens light flux reaching the focusing screen are different, when the viewfinder optical system is zoomed from WIDE to TELE, vignetting may occur in the viewfinder image. Even if the zoom lens is not the interchangeable lens, it is the same as the interchangeable lens in that the focal length is different.

It is an object of the present invention to provide a variable magnification type finder optical system in which vignetting of the finder image caused by varying the magnification of the finder optical system does not occur even when such a taking lens is attached. And

[0007]

In order to achieve the above object, the present invention is used in a trimmable single-lens reflex camera and has a zoom function for observing an image formed by a taking lens. The following conditions are satisfied in the optical system. − (EZ × 0.0107−0.01) ≦ (FW + BW) / FW ² − (FT + BT) / FT ² ≦ (EZ × 0.0107−0.01) However, EZ is the ratio of the largest state of the viewfinder optical system to the state in which the absolute value of the magnification is the smallest, and FW is the magnification of the viewfinder optical system. The distance from the image plane of the taking lens to the front principal point position of the finder optical system in the state where the absolute value is the smallest, and BW is the pupil position of the finder optical system in the state in which the absolute value of the magnification of the finder optical system is the smallest. To the rear principal point position of FT, FT is the distance from the image plane of the taking lens to the front principal point position of the finder optical system when the absolute value of the magnification of the finder optical system is the largest, and BT is the magnification of the finder optical system. The distance from the pupil position of the finder optical system to the rear principal point position of the finder optical system in the state where the absolute value is the largest.
In this case, the taking lens may be replaceable,
It may be a zoom lens. A variable-magnification relay optical system is used to display the primary image formed by the taking lens.
A configuration may be adopted in which a secondary image is formed and the secondary image is observed through the eyepiece lens. A condenser lens may be provided closer to the secondary image side than the relay optical system, and the power of the condenser lens may be selected so as to satisfy the above condition.
In this case, the following conditions should be further satisfied. EXT = (βW ² −βT ² ) / (βW · φW−βT · φT) where EXT is the distance from the image plane of the secondary image formed by the relay optical system to the exit pupil of the relay optical system, βW is the magnification of the relay optical system when the absolute value of the magnification of the viewfinder optical system is the smallest, βT is the magnification of the relay optical system when the absolute value of the magnification of the viewfinder optical system is the largest, and φW is the magnification of the viewfinder optical system. The power of the relay optical system in the state where the absolute value of the magnification is the smallest, and .phi.T are the power of the relay optical system in the state where the absolute value of the magnification of the finder optical system is the largest.

[0008]

According to such a constitution of the present invention, the primary image has a shape.
The height h on the focusing screen (where h is the magnification of the viewfinder optical system)
(Depending on the rate) to fine of WIDE and TELE
The angle difference α ′ formed with the entrance pupil is approximately α ′ = (h / INTW) − (h / INTT) = h {(FW + BW) / FW²-(FT + BT) / FT²} Becomes, and α is determined by the shooting lens side.
On the other hand, if −α ≦ α ′ ≦ α, then the viewfinder optical system enters the viewfinder entrance pupil.
It can be put in the eye tolerance range, so when zooming
Vignetting of the viewfinder image in can be prevented. The above conditions
In the formula,-(EZ x 0.0107-0.01) corresponds to α
, (FW + BW) / FW²-(FT + BT) / FT²  Corresponds to α '.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a finder optical system of a camera embodying the present invention. In FIG. 1, reference numeral 1 is a taking lens, which is usually attachable to and detachable from a camera body 4. Reference numeral 2 denotes a main mirror that guides the light that has passed through the taking lens 1 toward an upper finder optical system 3 and is provided inside the camera body 4. 5 indicates a film. An AF sub-mirror 6 directs a part of the light from the taking lens 1 to the AF (focus detection) module 7.

The finder optical system 3 has a focusing plate 8 serving as a primary image plane on which a primary image is formed by the taking lens 1, a first condenser lens 9, and a first condenser lens 9 which directs light from the condenser lens 9 forward. One mirror 10 and the first mirror 10
Second mirror 11 for directing light from the upper side, a relay system auxiliary lens 12 for forming a reduced virtual image of the primary image of the focusing screen 8 downstream of the focusing screen 8 and the relay system. The light from the auxiliary lens 12 is made parallel to the optical axis of the taking lens 1 and directed rearward, the zoom relay lens system 14 used for pseudo zoom, and the light from this zoom relay lens system 14 is directed downward. The fourth mirror 15 directed toward the second lens, the second condenser lens 16, the visual field frame 17 arranged at the position of the secondary image plane on which the secondary image is formed, and the light passing through the visual field frame 17 for photographing the lens 1 It is composed of a fifth mirror 18 which is parallel to the optical axis of the lens and is directed rearward, and a fixed eyepiece lens 19. Furthermore, a so-called infinder display for displaying the shutter speed, aperture value, etc. outside the field of view. Characters for display LCD for forming (liquid crystal display device) 2
0, an infinder submirror 21, and an infinder prism 22 are provided at the positions shown in the figure.
In addition, 23 has shown the pupil position.

In FIG. 1, the light flux passing through the taking lens 1 is bent upward by the main mirror 2 and forms an image on the focusing screen 8. The light flux that forms the primary image on the primary image plane on the focusing screen 8 is bent forward (toward the subject side) by the first mirror 10 via the condenser lens 9, and further bent upward by the second mirror 11 to be relayed. After passing through the system auxiliary lens 12, it is bent backward by the third mirror 13. Next, it passes through the zoom relay lens system 14, is bent downward by the fourth mirror 15, and is re-imaged on the field frame 17 via the condenser lens 16. The light flux forming the secondary image on the field frame 17 is directed rearward by the fifth mirror 18, and the eyepiece 1
The pupil position 23 is reached via 9. In this embodiment, the main mirror 2 and the first to fifth mirrors 10, 11, 13, 1 are used.
Since a total of 6 mirrors 5 and 18 are used and the number thereof is an even number, the inverted relationship of the images finally seen as the finder optical system does not change.

By moving the zoom relay lens system 14 in the front-rear direction (the optical axis direction of the photographing lens), the conjugate length from the primary image surface to the secondary image surface remains constant and the secondary image surface changes from the secondary image surface. The image magnification on the image plane changes according to the trimming magnification. In this embodiment, as will be described later, the image magnification of the zoom relay lens system 14 is 0.34 (WID
E) to 0.578 (TELE). Field of view frame 1
Since the light flux is regulated by 7, the light passes through the photographing lens 1 in the range indicated by the solid line during the WIDE, and passes in the range indicated by the broken line during the TELE. This indicates that the range of the solid line on the film 5 is the photographing range during the WIDE, and the range of the broken line during the TELE. Zoom relay lens system 1
The information of the photographing range based on the magnification of 4 is recorded at an appropriate position of the film 5 (for example, a predetermined portion 51 shown in FIG. 6) at the same time as the photographing, and the photographing range is extended at the time of printing so that the pseudo zoom by trimming photographing is performed. Enable shooting.

FIG. 2 is a lens configuration diagram showing the focusing screen 8 and its subsequent developments. The relay optical system (relay system auxiliary lens 12 + zoom relay lens system 1) of this embodiment is shown in FIG.
Details of 4) will be described. Here, the relay system auxiliary lens 1
2 is composed of one concave lens, and the zoom relay lens system 14 is composed of a biconvex positive lens in order from the object side.
It is composed of a group G1 and a second group G2 composed of a biconvex positive lens and a negative lens concave to the image side. These groups are on the optical axis from the WIDE end to the TELE end according to arrows 24 and 25 during zooming. To move.

The magnification of the entire relay optical system is 0.34 times in WIDE and 0.578 times in TELE, which is a reduction optical system, which makes it possible to make the secondary image surface smaller than the primary image surface. The optical path can be narrowed. Further, since the focal length of the eyepiece lens 19 becomes short in order to make the magnification equivalent to that of the conventional viewfinder optical system, the overall size can be made compact. The relay system auxiliary lens 12 reduces the primary image plane and creates a virtual image whose image position is closer to the pupil side. As a result, the substantial conjugate length of the zoom relay lens system 14 is shortened, and the magnification in WIDE → TELE is changed in the vicinity of the same magnification, so that the amount of movement of the zoom relay lens system 14 due to zooming can be reduced.

For example, as shown in FIG. 3A, the zoom relay lens system 14 has a primary image plane of 0.34 at the WIDE end.
When the relay system auxiliary lens 12 made of a concave lens as in this embodiment is inserted between the primary image plane and the zoom relay lens system 14 when designed as an optical system for reducing the image to a secondary image plane of double the size, As shown in FIG. 3B, the reduced primary image 26 is formed as a virtual image at a point downstream (pupil side) of the focusing screen 8 (primary image plane). And this reduced one
If the next image 26 is about 0.485 times, the magnification of the zoom relay lens system 14 may be about 0.7 times.

On the other hand, according to the same principle, the magnification of 0.
In order to realize 578, the zoom relay lens system may have a magnification of about 1.19 times.

As is well known, when a zoom lens system is designed so that its magnification changes by sandwiching 1,
Since the amount of zoom movement is the smallest, it is possible to insert 0.7 (W) by inserting the relay system auxiliary lens 12 as described above.
Since the magnification can be set to (IDE) to 1.19 (TELE), the amount of movement of the zoom relay lens system 14 can be reduced, and the dimension of the finder optical system in the front-rear direction can be made more compact accordingly. That is, it is necessary for the zoom relay lens system 14 to be aligned on one axis by disposing the third mirror 13 between the relay system auxiliary lens 12 and the zoom relay lens system 14 as shown in FIG. The length in the front-rear direction is short, but since the amount of movement of these lenses is further reduced, the length required in the front-rear direction is short even if the lens movement space is taken into consideration. A compact configuration is possible.

The secondary image reduced and formed on the secondary image plane of the field frame 17 by the relay optical system is magnified and observed by the eyepiece lens 19. At this time, in order to secure a certain degree of magnification, the eyepiece lens. Since the magnification of 19 is high, the focal length of the eyepiece lens 19 can be short.

Next, the finder display optical system will be described. First, the display light from the LCD 20 is reflected by the finder sub-mirror 21 and enters the finder prism 22. The infinder prism 22 is a lens having a negative power on the incident surface, and thereby forms a reduced image of the LCD 20 at a position having the same optical distance as that of the secondary image surface. Infinder prism 22
The LCD image reduced by is passed through a part of the fifth mirror 18 which is not seen, and is seen through the eyepiece lens 19 to the lower part of the visual field.

Since the focal length of the eyepiece lens 19 of the present embodiment is about 1/3 of that of the eyepiece lens of the conventional single-lens reflex camera, the reduced image of the LCD 20 is produced by the conventional single-lens reflex camera. If you use the LCD used for other purposes without reducing it, it will look about 3 times larger. With this, it is not possible to provide a larger amount of information due to the limitation of the size of the field of view. In this case, if the pattern of the LCD 20 is made finer, the same amount of information as the conventional one can be provided, but since it is difficult at the current technical level, it is necessary to provide a large amount of information in the conventional fine pattern. In the embodiment, the reduction optical system is used as the infinder display optical system.

By the way, the taking lens 1 is generally of an interchangeable type, and various focal lengths are attached to the camera body 4. Even if it is not an interchangeable lens, the zoom lens is the same as the interchangeable lens in that the focal lengths are different. In this example,
Even when such a taking lens is mounted, vignetting of the finder image due to the magnification change of the finder optical system 3 is prevented from occurring, and this point will be described in detail below.

FIG. 5 shows an optical state from the taking lens 1 to the focusing screen 8. The photographic lens 1 is replaceable, and various focal lengths and FNO (F number) lenses are attached. These have different exit pupils, and the directions of the lens light flux reaching the focusing screen 8 are different. The taking lens of a conventional single-lens reflex camera (135 film) has an exit pupil position mainly from 50 mm to 100 mm from the focal plane, and a large FNO is about FNO = 4 to 5.6. FIG. 5 shows exit pupil positions D1 = 50 mm, FN1 = 4, exit pupil positions D2 = 100 mm, and exit pupils E1 and E2 at FN2 = 5.6. At the position of height h on the focusing screen 8, the range where the light flux comes from either exit pupil is the shaded portion 30, and the angle formed by this light flux is α. The maximum height h in standard time (WIDE) is about 20 m with 135 film.
When the trimming ratio is m and the maximum trimming magnification is 1.7 times during the trimming (TELE), the height h during the trimming is 11.8 mm. α is approximately represented by α≈ (1 / 2FN2) + (1 / 2FN1) + {(1 / D2)-(1 / D1)} h = 0.096 (radian) (1).

This light beam is bent by the Fresnel lens on the focusing plate 8 through the finder optical system 3 so that the light reaches the pupil. Even if the Fresnel lens bends the light beam, the angle α of the light beam (the angle formed by the light beam in the shaded portion 31) hardly changes. The actual focusing screen 8 has a diffusing surface, but recent focusing screens have low diffusivity because they improve the brightness of the finder optical system, and the spread of the luminous flux width due to diffusion cannot be expected.

In this embodiment, the focal length of the finder optical system 3 is changed by changing the magnification of the zoom relay lens system 14 in the finder optical system to change the finder magnification. The pupil seen from the reticle 8 side (that is, the place to observe with the eyes placed)
The position of the virtual image (hereinafter, the entrance pupil of the finder optical system 3) changes.

For example, even if the Fresnel lens on the focusing screen 8 is directed toward the entrance pupil of the finder optical system during WIDE, when the lens is set to TELE by zooming, if the entrance pupil of the finder optical system moves out of the light beam, the pupil will eventually reach the pupil. The light does not reach, and vignetting of the viewfinder image occurs. In order not to cause vignetting, even if WIDE changes to TELE or vice versa, the entrance pupil may move only within the entrance pupil allowable range W of the finder optical system 3 in FIG.

For the entrance pupil position INT of the finder optical system, the distance from the focusing screen 8 to the position of the front principal point to the finder optical system (the right side (pupil side) measured from the focusing screen is positive) is F,
If the distance from the pupil position to the rear principal point position of the viewfinder optical system (measured from the pupil) and B, INT = F + 1 / {(1 / -B) -1 / F} = F 2 / (F + B) ...... (2) When subscripts W and T are added to WIDE and TELE, respectively, the difference in angle between the height h on the focusing screen 8 and the view pupil entrance pupil of WIDE and TELE is approximately α '= (h / INTW). − (H / INTT) = h {(FW + BW) / FW ² − (FT + BT) / FT ² } (3) Where FW is the distance from the image plane of the taking lens to the front principal point position of the finder optical system in the state where the absolute value of the magnification of the finder optical system is the smallest, and BW is the state in which the absolute value of the magnification of the finder optical system is the smallest. The distance from the pupil position of the finder optical system to the rear principal point position of the finder optical system, FT is the distance from the image plane of the taking lens to the front principal point position of the finder optical system when the absolute value of the magnification of the finder optical system is the largest. The distance, BT, is the distance from the pupil position of the finder optical system to the rear principal point position of the finder optical system when the absolute value of the magnification of the finder optical system is the largest.

If this is -α≤α'≤α with respect to α determined by the taking lens side, the entrance pupil of the finder optical system can be within the finder entrance pupil allowable range W. When the trimming ratio is 1.7, the height h is h = 1.
Since 1.8 and α = 0.096 from the above formula (1), (FW + BW) / FW ² − (FT + BT) / FT ² (4) is −0.008 ≦ (FW + BW) / FW ² It is sufficient to satisfy − (FT + BT) / FT ² ≦ 0.008 (5).

The value of ± 0.008 in the conditional expression (5) varies depending on the zoom ratio (trimming magnification) by the pseudo zoom, that is, the ratio EZ of the maximum state to the minimum state of the viewfinder optical system. Then, ± (EZ × 0.0107−0.01) (6) That is, the expression (5) is more generally expressed by-(EZ × 0.0107-0.01) ≦ (FW + BW) / FW ² − (FT + BT) / FT ² ≦ (EZ × 0.0107−0.01) (7)

The value of the equation (6) is the value of the trimming magnification EZ and is as shown in the table below. Value of EZ (2) equation 1.4 ± 0.005 1.7 ± 0.008 2.0 ± 0.011 Equation (6) increases as the value of EZ increases (allowable range W increases). Since the amount of movement of the lens for zooming increases, the finder entrance pupil may move more greatly, which makes designing difficult.

In the case of the finder optical system including the relay optical system as in this embodiment, the value of the expression (4) can be put into the condition (7) by adjusting the power of the second condenser lens 16. it can. EXT is the distance from the image plane of the secondary image formed by the relay optical system to the exit pupil of the relay optical system, and βW is the magnification of the relay optical system in the state where the absolute value of the magnification of the finder optical system is the smallest. , ΒT is the magnification of the relay optical system when the absolute value of the magnification of the finder optical system is the largest, and φW is the power of the relay optical system when the absolute value of the magnification of the finder optical system is the smallest, φ
Let T be the power of the relay optical system when the absolute value of the magnification of the finder optical system is the largest, then EXT = (βW ² −βT ² ) / (βW · φW−βT · φT) If the power of the second condenser lens 16 is adjusted so as to be close to the conjugate relationship with the entrance pupil position, W
Since IDE and TELE have the same entrance pupil of the entire finder optical system, the value of the expression (4) can be brought close to zero.

[0031] In this embodiment FW = - 78.75 BW = + 135.75 FT = - 43.40 BT = + 64.14 (FW + BW) / FW 2 - (FT + BT) / FT 2 = -0.0018 , and the Enough to enter the conditional expression.

As an optical system for varying the magnification of a conventional finder optical system, a type in which a magnifying lens is inserted between a pentaprism and an eyepiece lens is considered as in JP-A-57-74719. Instead of increasing the magnification for the pseudo zoom as in the present invention, the central portion of the viewfinder is magnified and viewed. Considering the standard time as WIDE and the magnifying time as TELE, the condition of the expression (7) is When it is calculated whether or not it is satisfied, for example, Example 3 of the known example
Then, the magnification ratio is 1.538, which is lower than that of the present invention, and the value of the expression (6) is ± 0.006, but FT = 36.02 BT = -36.38 FW = 55.96 BW = -25.2 FW + BW) / FW ² − (FT + BT) / FT ² = 0.0101> +0.006, which deviates from the condition (7). If such an optical system is used for changing the magnification of the pseudo zoom, vignetting will occur around the screen at the time of enlarging, which is not suitable.

Further, JP-A-1-319723 and JP-A-1-319723.
No. 319724 and Japanese Patent Laid-Open No. 1-319725 are types in which the focal length of the eyepiece lens is variable in a conventional finder optical system having a pentaprism, but they all have a small magnifying power of less than 1.2. However, the above condition (7) is barely reached, and if an attempt is made to increase the zoom ratio by the same method, the condition (7) is deviated from. If the pseudo zoom is less than 1.2 times, the effect of enlarging the finished photograph is very small, and the effect is felt when the enlarging magnification is about 2 times in area, that is, the zoom ratio is about 1.
4 times or more is necessary.

Although it is difficult to construct an optical system having a magnification of 1.4 times or more by the methods of these known examples, even if it is possible, the finder entrance pupil moves largely and the condition (7) is not satisfied. The table below shows the calculation results of these publicly known examples (however, for all the first examples of each publicly known example). EZ Value of Expression (6) Value of Expression (4) H1-319723 1.10 ± 0.0018 +0.0019 H1-319724 1.11 ± 0.0019 +0.0015 H1-319725 1.17 ± 0.0025 +0 As can be seen from this table, Japanese Patent Laid-Open No. 1-319724 enters the condition at the last minute, but Japanese Patent Laid-Open No. 1-31972
No. 3 and Japanese Patent Application Laid-Open No. 1-319725 are out of the conditions.

In the present embodiment shown in FIG. 1, without the first condenser lens 9, the finder entrance pupil when designed as described above becomes short (about 50 mm), and as shown in FIG. It cannot be bent in the direction of the entrance pupil of the finder optical system only by the Fresnel lens on the focusing screen 8. Therefore, the first condenser lens 9 is introduced to fulfill the role of further bending the light beam bent by the Fresnel lens. When the first condenser lens 9 is added to the finder optical system, the entrance pupil position of the finder optical system is approximately 95 mm (WIDE) to 110 mm.
(TELE). The position of the entrance pupil is adjusted by the second condenser lens 16 so as to satisfy the conditional expression (7).

Finally, Table 1 shows data of the finder optical system of this embodiment. In this table 1, r1, r2, ... r
20 is a radius of curvature of the surface counted from the object side as shown in FIG. The surfaces corresponding to r6, r9 and r16 are aspherical surfaces, and the aspherical surface coefficients A4, A6 and A8 are shown in Table 2.
Shown in. In Table 1, d1, d2, ... D19 are the distances between the upper surfaces of the respective axes, N1, N2 ,.
1, ν2, ... ν9 are Abbe numbers for the d-line.

<Table 1> [Radius of curvature] [Space between upper surfaces of the shaft] [Refractive index] [Abbe number] r1 Fresnel d1 1.500 N1 1.4914 ν1 57.82 r2 Acute d2 0.500 r3 94.160 d3 4.300 N2 1.4914 ν2 57.82 r4 -199.144 d4 38.200 r5 -27.051 d5 1.000 N3 1.805 ν3 40.97 r6 818.000 d6 T5 (variable) r7 17.125 d7 4.000 N4 1.4914 ν4 57.82 r8 -28.243 d8 T7 (variable) r9 13.433 d9 4.000 N5 1.4914 ν5 57.82 r10 -21.921 d10 0.500 r11 23.361 d84. ν6 23.82 r12 8.241 d12 T11 (variable) r13 64.144 d13 3.000 N7 1.584 ν7 31 r14 21.186 d14 0.500 r15 ∞ d15 19.246 r16 25.394 d16 1.200 N8 1.7985 ν8 22.6 r17 18.761 d17 0.800 r18 17.304 d18 4.500 N9 1.4914 15.-17.365 r82. r20 ∞

<Table 2> Aspherical surface EPS A4 A6 A8 ASP6 -3.745 0 0 0 ASP9 -11.180 0 0 4.8E-09 ASP16 1.000 -8.5E-05 0 0

[0039]

As described above, according to the viewfinder optical system of the present invention, the range of the entrance pupil of the viewfinder of WIDE to TELE is specified within the range where vignetting, which is determined by the conditions of the taking lens, does not occur. Therefore, there is an effect that vignetting of the finder image does not occur when the magnification of the finder optical system is changed even if the taking lens is changed, which is extremely effective.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a finder optical system embodying the present invention.

FIG. 2 is a lens configuration diagram in which a primary image and subsequent images of the finder optical system are developed and drawn.

FIG. 3 is a diagram showing the relay optical system portion.

FIG. 4 is an aberration diagram of the finder optical system in FIG.

5A and 5B are views for explaining the conditions and the like in which vignetting of the finder image does not occur due to zooming of the relay optical system in the present embodiment.

FIG. 6 is a diagram for explaining a trimming camera system.

[Explanation of reference numerals] 1 shooting lens 2 main mirror 3 viewfinder optical system 4 camera body 5 film 8 focusing plate 9 first condenser lens 10 first mirror 11 second mirror 12 relay system auxiliary lens 13 third mirror 14 Zoom lens system 15 4th mirror 16 2nd condenser lens 17 Field frame 18 5th mirror 19 Eyepiece 20 LCD 21 Infinder submirror 22 Infinder prism 23 Pupil position

Claims (1)

Claim: What is claimed is: 1. A finder optical system having a variable magnification function for observing an image formed by a photographing lens, which is used for a single-lens reflex camera capable of trimming,
Finder optical system characterized by satisfying the following conditions :-( EZ × 0.0107-0.01) ≦ (FW + BW) / FW ² − (FT + BT) / FT ² ≦ (EZ × 0.0107−0.01) However, EZ is the ratio of the largest state of the viewfinder optical system to the state in which the absolute value of the magnification is the smallest, and FW is the magnification of the viewfinder optical system. The distance from the image plane of the taking lens to the front principal point position of the finder optical system in the state where the absolute value is the smallest, and BW is the pupil position of the finder optical system in the state in which the absolute value of the magnification of the finder optical system is the smallest. To the rear principal point position of FT, FT is the distance from the image plane of the taking lens to the front principal point position of the finder optical system when the absolute value of the magnification of the finder optical system is the largest, and BT is the magnification of the finder optical system. The distance from the pupil position of the finder optical system to the rear principal point position of the finder optical system in the state where the absolute value is the largest. 2. The viewfinder optical system according to claim 1, wherein the viewfinder optical system has a zoom ratio of 1.4 times or more. 3. The viewfinder optical system according to claim 1, wherein the taking lens is replaceable. 4. The viewfinder optical system according to claim 1, wherein the taking lens is a zoom lens. 5. A variable-magnification relay optical system is used to form a secondary image of the primary image formed by the taking lens, and the secondary image is observed through an eyepiece. The finder optical system according to claim 1. 6. A condenser lens disposed on the secondary image side of the relay optical system, the power of the condenser lens being selected so as to satisfy the above condition. The finder optical system according to claim 5. 7. The finder optical system according to claim 6, further satisfying the following condition: EXT = (βW ² −βT ² ) / (βW · φW−βT · φT) where EXT is The distance from the image plane of the secondary image formed by the relay optical system to the exit pupil of the relay optical system, βW is the magnification of the relay optical system when the absolute value of the magnification of the finder optical system is the smallest, βT Is the magnification of the relay optical system when the absolute value of the magnification of the finder optical system is the largest, φW is the power of the relay optical system when the absolute value of the magnification of the finder optical system is the smallest, and φT is the power of the finder optical system. This is the power of the relay optical system in the state where the absolute value of the magnification is the largest.