Single lens reflex cameras and viewfinder display switchover devices therefor

The disclosed single lens reflex camera includes a shutter dial and a pentaprism as well as an eyepiece, and forms an image of a scene in the camera's field of view and a data image near the scene image through the eyepiece by passing data light from the vicinity of the pentaprism into the interior of the pentaprism. A display switchover device includes a transmission arrangement on the shutter dial for transmitting the motion of the dial, a linkage arrangement engageable with the transmission arrangement to be actuated on the basis of the selected position of the shutter dial, and a display selector between the pentaprism and the eyepiece and actuated by the linkage arrangement to control the direction of the data light to the eyepiece. According to an embodiment, the selector includes a subprism having a surface from which the data light from the pentaprism is reflected and another surface for directing the data light to the eyepiece, and a reflector that faces the two subprism surfaces for changing the reflecting position in response to the linkage arrangement.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to single lens reflex cameras and viewfinders for 
single lens reflex cameras in which data images are displayed with the 
image of a scene by passing data light into the camera's pentaprism, and 
more particularly to display changing devices for such viewfinders. 
2. Description of the Prior Art 
In general, automatic exposure cameras may operate in one of two modes, 
namely a shutter time priority mode or an aperture priority mode. In 
so-called dual priority cameras, operable in either one of these modes, 
the display of exposure information in the camera's viewfinder must be 
switched depending upon the selected exposure mode. That is, in the 
shutter time priority mode, it is necessary to display the preset value of 
the shutter time and an aperture value computed on the basis of the object 
brightness. Conversely, in the aperture priority exposure mode, the 
viewfinder must display the preset aperture value and the shutter time 
computed on the basis of the object brightness. However, such data may 
each be displayed by using a meter with a scale. In the shutter priority 
mode, the exposure data may be displayed at one side margin of the field 
of view image. In the aperture priority mode, the exposure data may be 
displayed in the lower margin of the field of view image. If both exposure 
data appear simultaneously, the displayed data may be confusing to the 
photographer. In other words, when the exposure data are to be displayed 
in such a manner, it is desirable to control the presentation so that one 
set of data is displayed and the other is extinguished. 
Various types of display switchover devices for presenting and cancelling 
exposure data are known. These may use a changeover mechanism which is 
actuated by an operating member provided in the camera body for 
extinguishing the displayed data. However, conventional switchover devices 
generally involve placing a shutter member in the data light path to make 
the displayed information disappear, and by operatively connecting the 
operating member to the shutter by means of wire or other device. 
Therefore, conventional switchover devices in a finder raise the problem 
of increasing the size of the finder to allow for space in which the 
shutter member may move. This complicates the mechanism. Furthermore, 
because the operative connection between the shutter member and the 
operating member in such switchover devices must be established with the 
use of a wire or the like, it cannot be used with interchangeable finders 
decoupleable from single lens reflex cameras. In prior single lens reflex 
cameras using interchangeable viewfinders, such display switchover devices 
had to be located entirely within the camera body, thereby sacrificing the 
simplicity of the latter. 
SUMMARY OF THE INVENTION 
With the foregoing in mind, an object of the present invention is to 
provide a display changeover device for a single lens reflex camera which 
has achieved the possibility of including a changeover mechanism for 
extinguishing the display of exposure information in the finder and which 
even when applied to an interchangeble finder, can change the display 
depending upon the position of the operating member that is included in 
the camera body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will next be described in greater detail in 
connection with embodiments thereof by reference to the drawings. 
In FIG. 1, the camera is composed of a camera body 1, is an objective lens 
2, a shutter dial 3 forming part of a shutter time presetting mechanism, 
an actuator pin 4 mounted on the shutter dial 3, an interchangeable finder 
5 for attachment to the camera body 1 and a sensor member 6 to react to 
the actuator pin 4 when the information display is changed. 
FIG. 2 illustrates a practical example of the mechanical structure of the 
interchangeable finder 5 attached to the camera body 1. The shutter dial 
3, actuator pin 4 and sensor member 6 are those illustrated in FIG. 1. A 
slide 7, fixedly carrying the sensor member 6 and having elongated slots 
7a which respective pins 8 mounted on a base plate 9 penetrate, is 
slidably movable on the surface of the base plate 9 and guided by the pins 
8. 
The slide plate 7 has an extension 7b engaging a lever 10. A lever 10 is 
pivotally mounted on a pin 11 on the base plate 9. A resilient member 12 
(for example, torsion coil spring) urges the lever 10 clockwise. The lever 
10 while, on one hand, engaging the extension 7b, on the other hand, 
engages a radial extension 13a of a rocking member 13 which fixedly 
carries a flat mirror 23 (see FIGS. 7 and 8). The rocking member 13 is 
pivotally mounted at stubs 14a on a support member 14. Again the support 
member 14 has an extension 14b on which is movably mounted an adjusting 
member (for example, a set screw). 
Further provided in the above-described rocking member 13 is a cutout 
portion 13b at which is connected one end of a resilient member 16 (for 
example, a coil spring) which urges the rocking member 13 
counterclockwise. The opposite end of the resilient member 16 is connected 
to the base plate 9. A meter 17 receives a lead wire 17b electrically 
connected through a terminal (not shown) to the camera body. A display 
member 18 with a shutter time scale rests on supporting legs therefor. An 
adjusting member 19 for a flat mirror 27 (see FIG. 3) adjusts the angle of 
the flat mirror 27 to correctly direct data light to a pentaprism 21. 
In FIGS. 3 and 4, the pentaprism 21 directs, rays of light radiated from an 
image of an object to be photographed on a focusing screen (not shown) to 
a sub-prism 22 and is therefrom directed to an eyepiece 24. The sub-prism 
22 has parallel flat permeable surfaces 22a and 22b, downwardly of which 
are reflection surfaces 22c and 22d, and has an upper permeable surface 
22e. And, these reflection surfaces 22c and 22d are mirrored by a 
reflection coating of, for example, aluminum. The permeable surface 22a is 
cemented to the rear or exit face 21a of the pentaprism 21. This permeable 
surface 22a may be otherwise spaced from the exit face 21a a small 
distance, but the cemented form has the advantage that handling of both 
the prisms becomes easier. Member 23 is the above-described rockingly 
mounted flat mirror with its reflection surface 23a mirrored by depositing 
a reflection coating of aluminum or the like. A triangular prism 25 has 
permeable surfaces 25a and 25c and a reflection surface 25b. The 
triangular prism 25 is cemented with its permeable surface 25a to the 
front upper slant face 21b of the pentaprism 21 at almost the center of 
the area thereof. Displays 17a and 18 are means for displaying information 
representing the above-described shutter time, and a warning of whether or 
not the exposure adjustment is out of range. The information display means 
17a and 18 gives off light L which after having passed through the 
permeable surface 25a of the triangular prism 25 is then reflected by the 
reflection surface 25b to the permeable surface 25c and from there is 
directed through the front upper slant face 21b of the penta-prism 21 to 
the lower margin of the exiting face 21a. After having emerged from this 
exiting face 21a, the light L enters the sub-prism 22 at the permeable 
surface 22a and is then reflected from the reflection surface 22c to the 
permeable surface 22e. After having emerged from this surface 22e, it is 
reflected by the reflection surface 23a of the flat mirror 23 which is 
positioned to face at the surface 22e, and then again enters the sub-prism 
22 at the surface 22e. After that, it is reflected by the reflection 
surface 22d to the permeable surface 22b and is therefrom directed to the 
eye-piece 24. A concave lens 28 has its second surface 28b cemented to the 
front upper slant face 21b of the pentaprism at the side thereof. The 
concave lens 28 and the preceding triangular prism 25 are arranged in a 
row in a direction perpendicular to a plane including an edge line of 
division of the roof faces of the pentaprism 21, i.e., perpendicular to 
the paper of FIG. 3. In the illustrated embodiment, a reflection member 27 
is in the form of a flat mirror, and a reflection member 26 in the form of 
a rhombic prism mirror. The rhombic prism 26 has two reflection surfaces 
26a and 26b and two permeable surfaces 26c and 26d and is positioned near 
the front upper slant face 21b of the penta-prism 21 at a location such 
that one of the reflection surfaces 26a occupies almost the center of the 
length in the lateral direction. Data 2a on the outer periphery of the 
barrel of the objective lens 2 is in the illustrated embodiment in the 
form of an aperture scale on the diaphragm presetting ring. Display 
information light M from the aperture scale 2a enters the rhombic prism 26 
at the permeable surface 26c as shown in FIG. 4 and is then reflected 
sidewards by one of the reflection surfaces 26a of this prism. After that, 
the information light M is reflected upwards by the other reflection 
surface 26b, and exits from the permeable surface 26d of this prism. Then, 
it is reflected by the reflection surface 27a of the flat mirror 27 to the 
concave lens 28. After having been refracted by this concave lens 28, it 
enters at the front upper slant face 21b of the penta-prism 21 and is 
directed therethrough to the lower margin of the exit face 21a thereof at 
almost the same angle as the other display information light L. Thus, the 
information light M emerging from the rear face 21a of the prism 21 
travels in a path similar to that of the display information light L 
before reaching the eye-piece 24. Hence, as shown in FIG. 6, data 2a 
appear as displayed information 2a ', and the data 17a, 18 appear as 
displayed information 17a', 18' in side-by-side relation in predetermined 
positions below the image F in the field of view. 
In FIG. 3, a phantom outline 23' indicates a turned position of the flat 
mirror 23. As the flat mirror 23 is turned from the solid line position, 
the information bearing light beam is deflected so as not to proceed to 
the reflection surface 22d of the sub-prism 22. Then the display of data 
2a' and 17a', 18' is extinguished before the photographer looking through 
the eye-piece. 
Also the above-described pentaprism 21 as shown in FIG. 4 is slanted in one 
side of the bottom entrance face thereof to form a pearmable surface 21c. 
A triangular prism 29 has permeable surfaces 29a and 29b and a reflection 
layer-coated surface 29c and is positioned with its permeable surface 29b 
opposite to the permeable surface 21c of the pentaprism at a small 
separation therefrom. Members 33, 34, 31a are information display 
arrangement such as a shutter scale, diaphragm scale, out-of-range 
warning, and meter needle. In the illustrated embodiment, 33 is a 
diaphragm scale; 34 is shutter time; and 31a is a meter needle. 
The information display members 33, 34, 31a together give off light N which 
passes enters the triangular prism 29 through a permeable surface 29a to 
enter this prism. Then, it is totally reflected by the permeable surface 
29b and then once more by the reflecting surface 29c through the permeable 
surface 29b. After having emerged from that surface 29b, it enters the 
above-described pentaprism 21 and passes therethrough in a path similar to 
that in which the finder image forming light passes until it reaches the 
eye-piece 24. Thus, the light N bearing data to be displayed presents 
itself as a display of informations 33', 34' and 31a' at the right hand 
side of the viewfinder image F as shown in FIG. 5. A shutter arrangement 
32 cooperates with the shutter dial 3 and, as far as the illustrated 
embodiment is concerned, upon selection of the aperture priority exposure 
mode places a symbol "A" on the shutter dial 3 in registry with an index 
to block the light N as shown by dashed lines in FIG. 6. The members 33, 
34 and 31a and the shutter arrangement 32 are included in the interior of 
the camera body. It is further noted that the operative connection between 
the shutter arrangement 32 and the shutter dial 3 is known and constructed 
as follows: The shutter dial 3 fixedly carries a first pulley rotatable 
along therewith, and the shutter arrangement 32 is provided with an 
actuator which is driven by a second pulley. The first and second pulleys 
are constrained by an endless wire to transmit motion of the first pulley 
to the second one, so that the shutter dial 3 is drivingly connected to 
the shutter arrangement 32. 
The operation of the embodiment of such construction is as follows. 
FIG. 7 illustrates the elements' positions where the display of 
informations appears below the field of view of the finder as shown in 
FIG. 6. The shutter dial 3 may be set in a position (in this instance, "A" 
position) where the camera is switched to the aperture priority exposure 
mode, and where the actuator pin 4 acts on the sensor member 6. As the 
slide 7 is moved to the left, the lever 10 is turned counterclockwise 
against the force of the bias spring 12, so that rocking member 13 its 
extension engaging with the lever 10 is freed therefrom to turn 
counterclockwise by the spring member 16. Such movement goes on until the 
extension 13a abuts the above-described adjusting member 15. Thus, the 
flat mirror 23 is oriented such that the information light from the 
reflection surface 22c of sub-prism 22 is returned to the prism at its 
reflection surface 22d. Therefore, the information light from the 
reflection surface 22c of sub-prism 22 is directed to the eye-piece 24 
when the shutter dial 3 is set in the aperture priority mode position ("A" 
position), and the information light is recognized within the finder as 
shown in FIG. 6. Also, at this time, the shutter means 32 blocks the 
triangular prism 29 from the information light so that the display of 
exposure information which is significant in the shutter priority exposure 
mode is not presented. In connection with the adjusting member 15, it need 
scarcely be said that it is better to carry out an adjusting operation of 
the member 15 during assembly with the resulting position of the displayed 
data 2a', 17a' and 18' optimum relative to the field of view of the 
finder. 
FIG. 8 illustrates another operative position where the shutter dial 3 is 
turned to move the symbol "A" representing the aperture priority exposure 
mode out of registry with the index. In this case, the actuator pin 4 is 
moved away from the sensor 6 to permit clockwise movement of the lever 10 
by the spring 12 as the slide 7 moves in the direction reverse of that 
described in connection with FIG. 7. In this case, the force of the spring 
12 which overcomes the force of the spring 16 turns the rocking member 13 
clockwise, so the flat mirror 23 is turned to a position where the 
information light from the reflection surface 22c of sub-prism 22 is not 
directed to the reflection surface 22d of said prism. Therefore, the 
display of data 2a', 17a' and 18' which occurs in the aperture priority 
exposure mode is extinguished from the vicinity of the field of view of 
the finder. On the other hand, at this time, the shutter arrangement 32 is 
retracted from the light path to the position shown in FIG. 4 so that when 
in the shutter priority exposure mode or the manual exposure mode, the 
display of informations 31a', 33' and 34 is presented. 
FIG. 9 illustrates another embodiment of the invention where a reversible 
opaque mask 41 (for example in the form of a thin plate with a light 
shielding property) is arranged to advance into and be drawn from the 
light path between the sub-prism 22 and flat mirror 23. This embodiment 
though capable of reducing ghost as compared with the first embodiment has 
a problem of requiring additional space. 
As described in greater detail above, according to the present invention, 
setting the shutter dial on the camera suffices either to readily 
extinguish the display of informations unnecessary to the selected 
exposure mode, or to present this display as need arises. Further, the 
device for switching between the presentation and extinction of the 
display of information can be constructed in a simple form that does not 
require a very large space, thus avoiding any increase in the bulk and 
size of the camera and finder. Furthermore, according to the present 
invention, even interchangeable finder type single lens reflex cameras, 
the selecting the presentation and extinction of a display data can be 
achieved with ease. This contributes to a simple operation of the camera.