GB2233774A - Mirror drive for a monocular reflex camera - Google Patents

Abstract

Mirror drive for a monocular reflex camera, comprising a first mirror holder (5), which carries a reflex viewing mirror (6) having an at least partly transparent zone, and the pivot axis of which is disposed on a pivoting lever (2) rotatably mounted at a fixed location in the camera casing, comprising also a second mirror holder (10), which carries a measuring mirror (11) and is pivotally journalled in such a manner that the measuring mirror, in the observation position of the mirror drive, deflects the light beams passing through the transparent zone of the viewing mirror onto a photoelectric measuring cell and, in the photographic position, bears against the rear face of the viewing mirror. Adjustable contact elements are provided for aligning the viewing mirror and the measuring mirror in the aforementioned observation position. The second mirror holder (10) is rotatably journalled independently from the first mirror holder (5) about a journal (9) provided on the pivoting lever (2) and can be tensioned, by means of a spring (14), against an adjustably mounted contact element (16; 23). <IMAGE>

Description

MIRROR DRIVE FOR A MONOCULAR REFLEX CAMERA This invention relates to a mirror drive for a monocular reflex camera having a first mirror holder, which carries a reflex viewing mirror having an at least partly transparent region and the pivot axis of which is disposed in the mariner of a crarshaft on a pivoting lever rotatably journalled in a fixed location in the camera casing, comprising a second mirror holder, which carries a measuring mirror and is pivotally journalled in such a manner that the measuring mirror, in the observation position of the mirror drive, deflects the light beams passing through the transparent zone of the mirror onto a photoelectric measuring cell and, in the photographing position, lies against the rear side of the viewing mirror, and comprising also adjustable contact elements for aligning the viewing mirror and the measuring mirror in their observation positions.

Viewing mirrors mounted in the manner of a crankshaft, i.e. on an axis that is not stationary, are advantageously suitable for the optimum utilization of the small space often available for the mirror movement, because these viewing mirrors can execute a combined rotational and sliding movement. Difficulties arise if a measuring mirror is also to be coupled with the movement of the viewing mirror.

In one known arrangement of the initially named type (DE-PS 26 26 150), the measuring mirror is rigidly fixed to the pivoting lever which carries the pivot axis for the viewing mirror. For changing the observation position of the viewing mirror, and adjustable stop is provided, by which changes in position of the measuring mirror can simultaneously be brought about. An adjustment of the position of the measuring mirror independently of the viewing mirror is not provided.

A further known arrangement (DE-OS 32 40 936) shows a measuring mirror, which is mounted rotatably on a viewing mirror which, in turn, is mounted in the manner of a crankshaft. To this extent, the measuring mirror is rotatably journalled via a double-link kinematic chain in the camera casing, so that when large scale mass production is aimed at, the aligning of the measuring mirror in a functionally secure measuring position is adversely affected.

An object of the present invention is, in a mirror drive of the type of this category, to create an improved arrangement for the measuring mirror.

According to the invention, there is provided a mirror drive for a monocular reflex camera, comprising a first mirror holder, which carries a reflex viewing mirror having an at least partly transparent zone, and the pivot axis of which is disposed on a pivoting lever rotatably mounted at a fixed location in the camera casing, comprising a second mirror holder, which carries a measuring mirror and is pivotally journalled in such a manner that the measuring mirror, in the observation position of the mirror drive, deflects the light beams passing through the transparent zone of the viewing mirror onto a photoelectric measuring cell and, in the photographic position, bears against the rear face of the viewing mirror, and also comprising adjustable contact elements for aligning the viewing mirror and the measuring mirror in the aforementioned observation position, characterised in that the second mirror holder is rotatably journalled independently from the first mirror holder about a journal provided on the pivoting lever and can be tensioned, by means of a spring, against an adjustably mounted contact element.

Preferably, the second mirror holder is rotatable in alternating sense by the spring out of a dead-centre position arranged between the observation position and the photographing position, the spring acting on one end on the second mirror holder and at its other end on the pivoting lever, and possesses a control arm which can be deflected in the sense of overcoming the aforementioned dead-centre position by a control cam disposed in the camera casing, during the movement of the pivoting lever between the observation position and the photographing position. Favourably, the control arm can be aligned in the observation position by the control cam disposed in the camera casing.In accordance with one advantageous embodiment, the control arm forms, together with the control cam, a contact pair, at least one contact element of the contact pair being adjustable in the sense of aligning the measuring mirror in the observation position. In a simple manner, the control cam is arranged to be adjustable.

The invention will now be described with reference to the accompanying drawings in which: FIGURE 1 shows a mirror drive in the observation position, FIGURES 2 and 3 show various sequential phases of the mirror drive, FIGURE 4 shows the mirror drive in the photographing position, and FIGURE 5 is a further form of embodiment.

In a camera casing, not illustrated in more detail, the pivoting lever 2 is rotatably journalled about the shaft 1, which pivoting lever is connected via the web 3 with a further pivoting lever of the same form. The further pivoting lever, not visible, is also rotatable about the shaft 1 at a distance from the plane of the pivoting lever 2. On the pivoting lever 2, the first mirror holder 5 for a reflex viewing mirror 6 is mounted rotatable about the pivot axis 4. The viewing mirror 6 can be aligned in the observation position by the adjustable stops 7 and 8 provided in the camera casing. The region 12 of the viewing mirror t is formed partly transparent to light. Also rotatably mounted about the journal 9 on the pivoting lever 2 is the second mirror holder 10, which carries a measuring mirror 11 behind the aforementioned transparent zone 12 of the viewing mirror 6.The second mirror holder 10 is rotatable with respect to the pivoting lever 2 in such a manner that the measuring mirror 11 is pivotal between a photographing position, bearing against the rear face of the viewing mirror 6 in the partly transparent zone 12, and an observation position, folded away from the viewing mirror 6. In the lower part of the camera casing, the measuring cell 13 is disposed, which can receive the light beams reflected by the measuring mirror 11 and convert them photoelectrically.

A spring 14 is attached with its one end to the pivoting lever 2 and, at a larger distances therefrom than the journal 9, is attached with its other end to the second mirror holder 10 in such a manner that, between the observation position of the measuring mirror 11 and its photographing position, there is a dead-centre position about the journal 9 and the second mirror holder 10 can be pivoted by the spring 14, on the one hand clockwise into the photographing position and on the other hand anticlockwise into the observation position. On the second mirror holder 10, the fork-shaped control arm 15 is provided, the control flanks 15a and 15b of which fit around the control cam 16. The control cam 16 is mounted on the control lever 18, rotatable about the pin 17.Through the elongated hole 19 of the control lever 18 passes a clamping screw 20, so that the control lever 18 can be secured in different positions. The control cam 16 forms, with the control flank 15b, a contact pair, the one contact element of which, namely the control cam 16, is adjustable relative to the other contact element, that is the control flank 15b.

The method of functioning of the arrangement is as follows: in the observation position of the mirror drive (see Fig. 1), the beam arriving from the left through an object glass is deflected by the viewing mirror 6 upwards into the searcher. The correct observation position of the viewing mirror 6 is adjusted by the stops 7 and 8. A part of the beam passes through the partly transparent zone 12 and reaches the measuring mirror 11, disposed behind the viewing mirror 6, which measuring mirror in turn deflects this part of the beam onto the photoelectric measuring cell 13. In this observation position, the control flank 15b bears against the control cam 16, because the spring 14 attempts to rotate the second mirror holder 10 anticlockwise about the pin 9.By loosening the clamping screw 20, the control lever 18 can be pivoted with the control cam 16, and the second mirror holder 10, journalled on the pivoting lever 2, can be brought with the measuring mirror 11 into the correct position.

If, for the purpose of making a photographic recording, the pivoting lever 2 is rotated upwards about the shaft 1, then the first mirror holder 5 together with viewing mirror 6 is rotated by the pivoting lever 2 via the pivot axis 4 and the second mirror holder 10 together with measuring mirror 11 is rotated by the pivoting lever 2 via the journal 9, the movements being direct and independent of each other. At the start of this movement (compare Fig. 2) the first mirror holder 5 is lifted off the stops 7 and 8, so that the first mirror holder 5 can rotate relative to the pivoting lever 2. The second mirror holder 10 initially remains, due to the spring 14, with its control flank 15b in contact with the control cam 16.

As the pivoting lever 2 pivots further upwards (compare Fig. 3) the journal 9 passes beyond the dead-centre position of the spring 14, so that the second mirror holder 10 is rotated clockwise on the pivoting lever 2. As this happens, the control flank 15a of the control arm 15 comes into bearing against the control cam 16. As soon as the photographing position is reached (compare Fig. 4), the viewing mirror 6 bears against the searcher frame 21 and the measuring mirror 11 bears against the rear face of the viewing mirror 6, the partly transparent region 12 of the viewing mirror 6 being covered.

The return of the mirror drive from the photographing position (compare Fig.

4) into the observation position (compare Fig. 1) takes place in the reverse direction. In this reversal, the second mirror holder 10 first remains at rest relative to the pivoting lever 2 due to the spring 14. It is only when, as a result of the downward pivoting of the pivoting lever 2, the dead-centre position of the spring 14 has been overcome, that the spring 14 rotates the second mirror holder 10 about the journal 9 independently of the combined rotational and displacement movement of the first mirror holder 5.

In accordance with a further embodiment (compare Fig. 5), the second mirror holder 10, rotatably journalled independently of the first mirror holder 5 on the pivoting lever 2, can be deflected by means of a stationary control cam 22 beyond the dead-centre position of the spring 14. The aligning of the second mirror holder 10 in the observation position is carried out here by the adjustable eccentric 23.

The invention is not limited to the examples of embodiment illustrated, but can be realized in other variants. The important feature is always that the second mirror holder 10 is rotatably connected with the pivoting lever 2, carrying the pivot axis 4, independently of the first mirror holder 5, journalled on a crankshaft-like pivot axis 4.

Claims (7)

CLAIMS:

1. Mirror drive for a monocular reflex camera, comprising a first mirror holder, which carries a reflex viewing mirror having an at least partly transparent zone, and the pivot axis of which is disposed on a pivoting lever rotatably mounted at a fixed location in the camera casing, comprising a second mirror holder, which carries a measuring mirror and is pivotally journalled in such a manner that the measuring mirror, in the observation position of the mirror drive, deflects the light beams passing through the transparent zone of the viewing mirror onto a photoelectric measuring cell and, in the photographic position, bears against the rear face of the viewing mirror, and also comprising adjustable contact elements for aligning the viewing mirror and the measuring mirror in the aforementioned observation position, characterised in that the second mirror holder (10) is rotatably journalled independently from the first mirror holder (5) about a journal (9) provided on the pivoting lever (2) and can be tensioned, by means of a spring (14), against an adjustably mounted contact element (16; 23).

2. Mirror drive according to claim 1, characterised in that the second mirror holder (10) can be rotated in alternating sense by the spring (14) out of a dead-centre position, disposed between the observation position and the photographing position, the spring (14) being attached with one end to the second mirror holder (10) and at its other end to the pivoting lever (2), and the second mirror holder possesses a fork-like control arm (15), which can be deflected by a control cam (16), mounted in the camera casing, during the movement of the pivoting lever (2) between the observation position and the photographing position, in the sense of overcoming the aforementioned dead-centre position.

3. Mirror drive according to Claim 2, characterized in that the control arm (15) can be aligned in the observation position by the control cam (16) mounted in the camera casing.

4. Mirror drive according to Claim 3, characterized in that a control flank (15b) of the control arm (15) forms, together with the control cam (16), a contact pair, at least one contact element (16) of the contact pair being adjustable in the sense of aligning the measuring mirror (11) in the observation position.

5. Mirror drive according to Claim 4, characterized in that the control cam (16) is constructed to be adjustable.

6. Mirror drive substantially as described with reference to Figures 1 to 4 and Figure 5 of the accompanying drawings.

7. A monocular reflex camera including a reflex mirror drive as claimed in any of claims 1 to 5.