Camera viewfinder

A viewfinder for a camera includes a near-subject frame visible in the finder field to frame subjects closer to the camera than a predetermined distance, e.g., four feet, and a normal frame visible in the finder field to frame subjects beyond that distance. The near-subject frame defines a subject-field that is offset from the subject-field defined by the normal frame to correct for the parallax error at close distances. A focus-setting device for the camera lens has a near-subject setting for close-up subjects and a distant-subject setting for other subjects. When the focus-setting device is set to its distant-subject setting, for use with the normal frame, the near-subject frame is not visible. This prevents the near-subject frame from being confused with the normal frame. The near-subject frame is only made visible in response to the focus-setting device being set to its near-subject setting. Making the near-subject frame visible alerts the photographer to use that frame instead of the normal frame.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to camera viewfinders for viewing and 
framing the subject to be photographed, and particularly to a bright-line 
viewfinder, sometimes called a brillant-frame finder. More specifically, 
the invention relates to a viewfinder having a near-subject (or parallax 
correction) frame and a distant-subject frame visible in the finder field 
to frame respective subjects closer to and farther from the camera than a 
predetermined distance, e.g., four feet. 
2. Description of the Prior Art 
When taking a picture it is necessary to know not only in what direction to 
aim the camera but also how much of the scene will be included in the 
picture. For this reason practically every modern camera has a viewfinder 
of some kind. 
Most modern cameras include an optical viewfinder which comprises a 
negative finder lens, and a positive eyelens mounted behind the negative 
lens, for viewing an erect image of the subject to be photographed. The 
limits of the field of view in the finder may be masked on the negative 
lens, and the scene is viewed through the finder with the camera held at 
eye level. In one popular viewfinder, known as the Albada finder, the 
concave curve on the negative lens is made partially reflective with a 
metalized coating, such as aluminum. The coating reflects a white frame 
defined by a series of rectangularly arranged slots in a black mask which 
surrounds the eyelens. The photographer sees the white frame as suspended 
in space superimposed over the scene viewed through the finder. The white 
frame surrounds the portion of the field of view in the finder which will 
be projected on the film. 
A more recent viewfinder somewhat similar to the Albada finder is the 
bright-line or brilliant-frame finder. In this viewfinder, a second window 
is provided adjacent the finder window. The second window is covered with 
a diffusing screen, and the rectangular series of slots is cut into a 
masking plate situated behind the screen. A prism or mirror behind the 
masking plate reflects a bright-line frame, formed by ambient light in the 
slots, onto a semi-reflecting mirror in the viewing path of the finder, 
and from there into the positive eyelens. This arrangement provides a 
brighter frame for the viewed subject as compared to the Albada finder. 
When the viewfinder, even though pointing in the same direction as the 
camera lens, takes in a field of view that is displaced relative to the 
view projected on the film, it suffers from a framing error. This is 
commonly referred to as the parallax error. It arises from the difference 
in viewpoint between the viewfinder and the camera lens, which may be one 
to two inches apart. With a distant subject which may have a subject-field 
of many feet or even yards, an inch or two is obviously insignificant. At 
close range, however, for instance with the camera lens focused at three 
feet, the subject-field may only be two to three feet wide. There, a 
couple of inches lost at the top of the scene may result in the cutting 
off of important subject matter. For this reason many cameras include some 
means for correcting for parallax in the finder. 
There are various ways of compensating for the framing error due to the 
finder parallax. The simplest is to cut down the finder field so that it 
always takes in less than the film. With distant subjects, the view 
projected on the film will then include more at the top than in the finder 
field, while at near distances there will be more recorded at the bottom 
of the picture than in the finder field. This solution is less than 
satisfactory since the photographer cannot be sure of the actual extent to 
which the subject-field will be recorded on the film. 
Bright-line finders usually have one of two types of correction for 
parallax. The simplest is a second bright-line frame that defines a 
subject-field which includes slightly more at the bottom and one side, 
with a corresponding reduction at the top and the other side, as compared 
to the subject-field defined by the normal bright-line frame. Thus, the 
second bright-line frame serves as a parallax correction frame for framing 
close-up subjects nearer to the camera lens than say four feet, and the 
normal bright-line frame is used to frame other subjects beyond that 
distance. In operation, the normal frame is used far more frequently than 
the parallax correction frame. 
Often, in bright-line finders having a parallax correction frame for 
framing close-up subjects and a normal frame for framing other subjects, 
the two frames are illuminated by ambient light in the viewing path, and 
therefore are both visible in the finder field at the same time. This may 
cause the photographer to confuse the parallax correction frame with the 
normal frame, or vice versa, especially when picture-taking must be done 
quickly. 
More advanced cameras have a bright-line finder in which a single 
bright-line frame is alternatively located in a normal position for most 
subjects and in a parallax compensation position for close-up subjects. 
Thus, only a single bright-line frame is ever visible in the finder. 
Typically, the mask for producing the bright-line frame is coupled to the 
focusing mechanism for the camera lens. This allows the bright-line frame 
to be shifted in the finder field to the appropriate position in 
accordance with the focus position of the camera lens. However, this 
arrangement is relatively complex from a mechanical standpoint, and 
therefore increases the manufacturing cost of the camera and the possible 
risk of a break-down. 
SUMMARY OF THE INVENTION 
The above-described problems relating to viewfinders are believed solved by 
the invention. According to the invention there is provided an improved, 
yet relatively simple, viewfinder for a camera. The viewfinder includes a 
near-subject frame visible in the finder field to frame subjects closer to 
the camera than a predetermined distance, e.g., four feet, and a normal 
frame visible in the finder field to frame subjects beyond that distance. 
The near-subject frame defines a subject-field that is offset from the 
subject-field defined by the normal frame to correct for the parallax 
error at close distances. A focus-setting device for the camera lens has a 
near-subject setting for close-up subjects and a distant-subject setting 
for other subjects. When the focus-setting device is set to its 
distant-subject setting, for use with the normal frame, the near-subject 
frame is not visible. This prevents the near-subject frame from being 
confused with the normal frame. The near-subject frame is only made 
visible in response to the focus-setting device being set to its 
near-subject setting. Making the near-subject frame visible alerts the 
photographer to use that frame rather than the normal frame. 
In keeping with the teachings of the invention, the normal frame may be 
made visible by ambient light in the viewing path of the finder which is 
reflected from the subject to be photographed. In contrast, the 
near-subject frame can only be made visible by artificial or ambient light 
directed from a location in the finder that is outside the viewing path. 
Such an arrangement is relatively simple and easy to manufacture as 
compared to the movable frame-mask described in connection with the prior 
art. 
In a preferred embodiment of the invention, a partially-reflecting mirror 
is disposed to transmit ambient light in the viewing path of the finder 
and to form respective images of the near-subject and normal frames by 
reflection. With such a mirror, it is possible to view a close-up or 
distant subject through the mirror with a frame image surrounding the 
viewed subject in superimposed relation. The near-subject and normal 
frames are supported on a common optical support, e.g., an eyelens, in the 
viewing path, and have respective partially-reflecting surfaces through 
which a close-up or distant subject may be viewed. The normal frame is 
positioned to reflect ambient light in the viewing path toward the mirror 
to cause a bright-line image of the frame to be formed by the mirror. The 
near-subject frame is positioned to reflect ambient light in the viewing 
path toward a location spaced from the mirror to prevent an image of that 
frame from being formed by the mirror. A light source, energizable in 
response to the focus-setting means being set to its near-subject setting, 
directs source light from outside the viewing path toward the near-subject 
frame, and from there the light is reflected toward the mirror to cause a 
bright-line image of the frame to be formed by the mirror. Thus, the 
near-subject frame can only be made visible in the finder by source light 
outside the viewing path, whereas the distant-subject frame is made 
continuously visible in the finder by ambient light in the viewing path.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention is described as being embodied in a 35 mm still camera. 
Because such photographic cameras are well known, this description is 
directed in particular to camera elements forming part of or cooperating 
directly with the preferred embodiment. It is to be understood, however, 
that camera elements not specifically shown or described may take various 
forms known to persons of ordinary skill in the art. 
Referring now to the drawings, FIG. 3 depicts focus-setting means for a 
camera lens as an autofocus system 1. The autofocus system 1 is a known 
type having a near-subject setting 3 for subjects closer to the camera 
lens than a predetermined distance, e.g., four feet, and a distant-subject 
setting 5 for subjects farther from the camera lens than the predetermined 
distance. When the autofocus system 1 is in its near-subject setting 3, a 
normally opened switch 7 is closed to energize a light-emitting diode 
(LED) 9 via a suitable power source 11. Conversely, when the autofocus 
system 1 is in its distant-subject setting 5, the switch 7 remains opened 
and the LED 9 is not energized. 
A bright-line viewfinder 13, sometimes called a brilliant-frame finder, is 
shown in FIG. 1. A finder housing 15 having opposite end openings 6 and 17 
encloses a plano-convex negative finder lens 18 and a biconvex positive 
eyelens 19. The two lenses 18 and 19 are optically aligned in a viewing 
path to view an erect image of a subject to be photographed. As shown in 
FIG. 2, the viewfinder includes a near-subject frame 21 visible in the 
finder field 23 to frame a subject closer to the camera lens than the 
predetermined distance, i.e., four feet; and a distant-subject frame 25 
visible in the finder field to frame a subject farther from the camera 
lens than the predetermined distance. The distant-subject frame 25 is 
depicted in FIG. 2 as four discrete frame sections which define a 
rectangular area 25a, i.e., a subject-field, in the finder field 23. In a 
simpler sense, the near-subject frame 21 is depicted in FIG. 2 as a single 
frame section which defines a rectangular area 21a in the finder field 23. 
The rectangular area 21a is slightly offset from the rectangular area 25a 
to compensate for the parallax error at close distances. As shown in FIG. 
2, the rectangular area 21a includes slightly more at the bottom and the 
left side, with a corresponding reduction at the top and the right side, 
as compared to the rectangular area 25a. The near-subject frame 21 is 
defined by a single partially-reflecting surface 27 coated on the inclined 
top of a raised portion 29 of the rear convex side 31 of the positive 
eyelens 19. The distant-subject frame 25 is defined by four 
partially-reflecting surfaces 33 coated on the rear convex side 31 of the 
eyelens 19. Since the respective frame surfaces 27 and 33 are partially 
reflecting, they will transmit ambient light in the viewing path, and 
therefore will not obscure the viewed subject in the finder field 23. 
As shown in FIG. 1, the near-subject frame 21 and the distant subject frame 
25 are located on a common optical support, i.e., the eyelens 19. This 
permits a relatively compact viewfinder to be designed. 
Partially-reflecting mirror means in the finder housing 15 is shown in FIG. 
1 as a curved glass mirror 35 which has a concave curved side 37 coated 
with a partially-reflecting surface 39. The mirror 35 is disposed in the 
viewing path of the finder 13 to transmit ambient light in the path and to 
form respective images of the partially-reflecting surfaces 27 and 33 of 
the near-subject and distant-subject frames 21 and 25. With such an 
arrangement, it is possible to view a close-up or distant subject through 
the mirror 35 with a frame image surrounding the viewed subject in 
superimposed relation. The four partially-reflecting surfaces 33 defining 
the distant-subject frame 25 are positioned in the viewing path to reflect 
ambient light in the path toward the partially-reflecting surface 39 of 
the mirror 35. This will cause a bright-line image of that frame to be 
formed by the mirror whenever ambient light is in the viewing path. The 
single partially-reflecting surface 27 defining the near-subject frame 21 
is positioned in the viewing path to reflect ambient light in the path 
toward a location spaced from the partially-reflecting surface 39 of the 
mirror 35. Thus, an image of that frame normally will be prevented from 
being formed by the mirror. 
The LED 9 is positioned in the finder housing 15 within a light shield 41 
to direct artificial light (when energized) from outside the viewing path 
toward the partially-reflecting surface 27 defining the near-subject frame 
21, and from there toward the partially-reflecting surface 39 of the 
mirror 35, to cause a bright-line image of the frame to be formed by the 
mirror. As described above, the LED 9 is only energized in response to the 
autofocus system 1 being set to its near-subject setting 3 for a close-up 
subject. 
OPERATION 
During normal operation of the viewfinder 13, the autofocus system 1 is set 
to its distant-subject setting 5, and the distant-subject frame 25 is made 
visible in the finder field 23 by ambient light in the viewing path. Since 
the LED 9 is not energized, the near-subject frame 21 is not visible in 
the finder field 23 (even though that frame is illuminated by ambient 
light in the viewing path). 
When, on occasion, the autofocus system 1 is set to its near-subject 
setting 3, the LED 9 is energized to make the near-subject frame 21 
visible in the finder field 23. Making the near-subject frame 21 visible 
alerts the photographer to use that frame instead of the visible 
distant-subject frame 25. 
While the invention has been described with reference to a preferred 
embodiment, it will be understood that various modifications may be 
effected within the ordinary skill in the art without departing from the 
scope of the invention. For example, instead of providing the LED 9 for 
directing artificial light from outside the viewing path to cause a 
bright-line image of the near-subject frame 21 to be formed by the mirror 
35, a shutter and optical fiber may be provided for directing ambient 
light from outside the viewing path for the same purpose. 
Instead of employing the autofocus system 1, a manually operated focusing 
mechanism may be used. The focusing mechanism could be a known type having 
a scale of distances or zones marked on it. When a particular distance or 
zone is opposite the scale reference arrow, the camera lens is focused on 
all objects at that distance or within that zone. 
If an automatic focusing mechanism is used, as in the preferred embodiment, 
a visual indicator may be provided to alert the photographer that the 
mechanism is set to its near-subject setting. The indicator serves as 
further means, in addition to the visible near-subject frame 21, for 
alerting the photographer to use that frame rather than the visible 
distant-subject frame 25. The indicator might, for example, comprise an 
optical fiber extending between the LED 9 and an exterior location on the 
finder housing 15.