JPH0618344Y2 - Real image finder mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a real image type finder mechanism of a camera, and more particularly to a finder mechanism which prevents dust from entering to obtain a clear image.

(Prior Art) In a lens shutter camera, an inverted Galilean type finder mechanism has been widely used as a compact and inexpensive finder mechanism. Generally, this type of finder mechanism has a structure for preventing dust from entering in order to obtain a clear image. Conventionally, as a structure to prevent the intrusion of dust, the entire finder optical system has a closed structure,
Alternatively, a method is adopted in which the entire camera exterior has a closed structure.

Further, in recent years, a lens shutter camera using a zoom lens has also been provided. A camera using a zoom lens has a large focal length and a large zoom ratio, and when a conventional reverse Galilean finder mechanism is combined with this camera, the finder mechanism becomes large and it is not suitable for a compact lens shutter camera. Therefore, in order to solve such a problem, it is considered to use a Keplerian type real image finder mechanism.

(Problems to be solved by the invention) However, in the Kepler-type finder mechanism, when the conventional closed structure is used to prevent the invasion of dust, the structure becomes large and the manufacturing cost can be reduced. difficult. Also, in the case of the Kepler type finder mechanism,
It is difficult to make the engaging portion between the zooming moving member and the drive mechanism into a completely closed structure, and there is a high possibility that dust may enter from this portion.

The present invention has been made in view of the above points, and an object thereof is to provide a real image type finder mechanism that can obtain a clear image with a simple structure at low cost.

(Means for Solving Problems) In order to achieve the above object, according to the finder mechanism of the present invention, a transparent protective member is arranged at a position facing the incident surface of the Porro prism with the image forming surface interposed therebetween, This protective member is fixed to the support frame of the Porro prism. Then, by forming the space portion formed between the incident surface of the Porro prism and the protective member including the support frame to be a substantially sealed space,
Dust is prevented from entering the vicinity of the image plane.

(Operation) According to the Keplerian real image finder, when the real image formed on the image plane is viewed by being inverted by the Porro prism, the diopter shifts greatly as the distance from the image plane increases. Therefore, even if dust enters a region away from the image plane, the dust does not enter the field of view. Therefore, as in the present invention described above, a clear viewfinder image can be obtained by sealing an appropriate area near the image forming surface to prevent dust from entering. Further, it is highly reliable, that is, a sealing structure that can reliably prevent the invasion of dust, because it is not necessary to form a sealing structure in the engaging portion between the zooming movement member and the drive mechanism, and only in a relatively narrow area. Can be achieved at low cost.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to the drawings.

1 to 4 show a Kepler-type real image type zoom finder mechanism according to an embodiment of the present invention.

As shown in FIGS. 1 and 2, the finder mechanism includes a frame body 10 holding a finder optical system. The frame body includes a main body 12 having a substantially rectangular tube shape and a support frame fixed to the base end of the main body. 14 and. The support frame 14 accommodates the louver optical system including the Porro prism 15 and the eyepiece lens 17 shown in FIG. Porro prism 15
The entrance surface 15a faces the base end of the main body 12, and the exit surface 1
5b is arranged so as to face the eyepiece lens 17. Note that FIG. 1 shows the Porro prism 15 viewed from the direction of arrow A in FIG.

The first group 16, the second group 18, and the third group 20 among the lenses of the finder optical system are housed in the main body 12.
The first group 16 is held by a first frame 22 fixed to the tip of the main body 12. Second group 18 and third group 20
Are held by the second and third frames 24 and 26, respectively, and these frames are arranged in the main body 12 so as to be movable along the optical axis direction of the lens. Furthermore, the main body 12
A fourth frame 28 is fixed between the base end of and the support frame 14. And by this fourth frame,
A flat plate-shaped cover glass 30 which constitutes a protective member in the present invention is held and positioned so as to face the entrance surface 15a of the Porro prism 15.

These frames 22, 24, 26, 28 are arm portions 22a, 24a, 26a, 28a protruding laterally from the main body 12.
Have respectively. Further, through holes extending along the optical axis direction of the optical system are formed in these arm portions,
The guide shaft 30 is inserted through these through holes. The tip of the guide shaft 30 is fixed in the through hole formed in the arm portion 22a of the first frame 22, and the base end portion extends through the through hole formed in the arm portion 14a of the support frame 14. ing. Therefore, the second and third frames 24, 2
The movement of 6 is guided by the guide shaft 30. Between the first frame 22 and the third frame 26, and the second
Tension springs 32 and 34 are installed between the frame 24 and the holding frame 14, respectively. In addition, the arm portion 24 a of the second frame 24 and the arm portion 2 of the third frame 26
Protrusions 24b and 26b are formed on 6a, respectively. Then, the protrusion 24 is urged by the urging force of the springs 32 and 24.
b and 26b are pressed against the cam surface of a zoom drive cam (not shown) provided between these protrusions. Therefore, the second group 18 and the third group 20 are moved to the tele mode position (Fig. 4A), the wide mode position (Fig. 4B), and the macro mode position (Fig. 4C) in conjunction with the movement of the drive cam. .

A screw hole 14b extending parallel to the optical axis of the optical system is formed in the arm portion 14a of the support frame 14, and a diopter adjusting screw 36 is screwed into this screw hole. Then, the tip of the screw 36 is brought into contact with the arm portion 28a of the fourth frame 28 to finely move the entire fourth frame along the guide shaft 30, so that the diopter of the finder can be adjusted.

As can be seen from FIG. 1, a visual field frame 38 is fixed between the fourth frame 28 and the holding frame 14, and is located between the cover glass 30 and the entrance surface 15 a of the Porro prism 15. The space between the cover glass 30 and the incident surface 15a is substantially airtightly sealed by the cover glass, the incident surface, and the fourth frame 28. The images picked up by the first to third groups 16, 18, and 20 of the optical system pass through the cover glass 30 and are sealed between the field frame 38 and the entrance surface 15a of the Porro prism 15, that is, sealed. An inverted real image is formed on the image plane 40 located in the space. This inverted real image is inverted and magnified by the loupe optical system including the Porro prism 15 and the eyepiece lens 17, and is observed as an erect normal image.

According to the finder mechanism configured as described above, the space between the cover glass 30 and the entrance surface 15a of the Porro prism 15, that is, the area near the image forming surface 40 is hermetically sealed to prevent dust from entering. There is. In the finder mechanism having the above-described optical system, the diopter of the loupe optical system including the Porro prism and the eyepiece lens is adapted only in the vicinity of the image forming surface 40. Therefore, unless the dust enters the vicinity of the image plane, that is, the space between the cover glass 38 and the incident surface 15a, the dust is not observed in the field of view of the finder. Therefore, according to the finder mechanism in which the area near the image plane is hermetically sealed, a clear finder image can be obtained.

Further, it is not necessary to provide a hermetically sealed structure around the movable members such as the second and third frames, and only the relatively narrow region between the cover glass and the Porro prism has to be hermetically sealed. Therefore, a highly reliable closed structure can be constructed at low cost.

(Effect of the Invention) As described above, according to the present invention, it is possible to reliably prevent the intrusion of dust that appears in the field of view of the finder, only by forming a closed structure in a very limited area near the image plane. Therefore, a finder mechanism having a clear finder image can be provided at low cost.

[Brief description of drawings]

1 to 4 show a finder mechanism according to an embodiment of the present invention, FIG. 1 is a sectional view showing a structure around an image plane, and FIG. 2 is a perspective view showing the whole finder mechanism. FIG. 4 is a perspective view of a Porro prism, and FIGS. 4A to 4C are views schematically showing different operation modes of an optical system. 10 ... frame body, 12 ... main body, 14 ... support frame, 15 ...
... Porro prism, 15a ... Incident surface, 30 ... Cover glass, 40 ... Imaging surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography Shou 59-119433 (JP, U) Seki 52-48428 (JP, U) Seki 35-15664 (JP, Y1)

Claims (1)

[Scope of utility model registration request] 1. A real image type finder mechanism in which an image forming surface is formed in front of the incident surface of a Porro prism, and a transparent protective film is provided at a position facing the incident surface of the Porro prism with the image forming surface sandwiched therebetween. The member is fixedly arranged on the support frame of the Porro prism, and the space formed between the incident surface of the Porro prism and the protective member including the support frame is formed to be a substantially closed space. Features a real image finder mechanism.