Focus detection apparatus with a light shielding member

A focus detection apparatus adapted to reform images of light fluxes that pass through differing regions of a photographic lens into a pair of images on light receiving element arrays by using, for each pair of images, a field mask, a field lens, a pair of re-imaging lenses and an aperture mask having a pair of aperture openings provided in the vicinity of the pair of re-imaging lenses. The focus detection apparatus has multiple focus detection blocks that detect the focus condition of the photographic lens from positions relative to the pairs of images. The focus detection apparatus is further adapted to detect the focus condition of multiple areas on a focal plane. The focus detection apparatus includes a deflection mirror positioned between the field lens and the pair of re-imaging lenses. The deflection mirror causes the light fluxes to be deflected at nearly right angles for focus detection. Finally, a light shielding member is positioned in a triangular space determined by a beam of light for focus detecting that is closest to the pair of re-imaging lenses, a beam of light for focus detecting that is closest to the field lens and a reflecting surface of the deflection mirror.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to multi-area focus detection apparatuses 
used in cameras. 
2. Description of the Related Art 
In the past, multi-area focus detection apparatuses which could 
simultaneously measure not only the axial area located on the optical axis 
of the photographic lens but also off-axial areas located far from the 
optical axis, were proposed as focus detection apparatuses to be used in 
cameras and in other optical devices. Such multi-area focus detection 
apparatuses typically include enough multiple focus detection optical 
systems to detect the focus condition of a corresponding number of single 
focus areas. The problems associated with such well-known systems and the 
methods implemented for resolving such problems, are indicated in Japanese 
Patent Publication No. 63-289513 (hereinafter the "JP-'513" reference). 
The conceptual composition of an embodiment of JP-'513 is shown in FIG. 4. 
The apparatus depicted in FIG. 4 detects the focus condition of the area on 
the optical axis of the photographic lens as well as two areas off the 
optical axis, for a total of three areas. In order to indicate the 
positions on the focal plane FP of the photographic lens TL, these areas 
have been arranged in an overall H shape such that area E1 is on the 
optical axis and extends horizontally on the focal plane FP. Area E1 is 
flanked by areas E2 and E3 which are off the optical axis and extend 
vertically on the focal plane FP. in each of these areas, the six light 
fluxes (LW1, LW2) through (LW5, LW6) pass through differing regions of 
photographic lens TL and thereafter pass through their respective field 
lenses L01 through L03. Images are formed on the light receiving parts 
(P1, P2) through (P5, P6) on the CCD line sensor PO based on the three 
pairs of re-imaging lenses (L1, L2) through (L5, L6). The focus condition 
of the photographic lens TL is detected in each area from the relation of 
the respective images. 
Field mask FM has openings E01 through E03 that regulate the range of the 
area to be used for detecting. Field mask FM is positioned directly in 
front of field lenses L01 through L03. Aperture mask AM has openings (A1, 
A2) through (A5, A6) onto which the emergent light pupil of the 
photographic lens TL is projected by field lenses L01 through L03 and by 
which the range of light fluxes to be used passes through the emergent 
light pupil are stipulated. Aperture mask AM is positioned in front of 
re-imaging lens L which is composed of three pairs of lenses (L1, L2) 
through (L5, L6). For any one area, for example area E1 on the optical 
axis, aperture E01 of field mask FM, field lens L01, the pair of openings 
(A1, A2) of aperture mask AM, and the pair of light receiving parts (P1, 
P2) of CCD line sensor P0 compose a focus detection optical system, and as 
a whole, the system takes a form that provides enough focus detection 
optical systems for the number of areas. 
With the aforementioned kind of focus detection apparatuses equipped with 
multi-area focus detection optical systems, there is a problem in that 
size constraints play a major role in the cost and implementation of such 
multi-focus systems. For example, because the light fluxes to be used are 
close together, trying to reduce the size of CCD line sensor P0 in order 
to make a compact device (when trying to make Q smaller in FIG. 4), light 
fluxes outside the corresponding areas, or so-called harmful light, falls 
on the light receiving part of the CCD sensors (LWh1, LWh2 etc. indicated 
by dotted lines in FIG. 4), and the precision of focus detection is 
reduced. Thus, in order to solve this problem, harmful light is shielded 
by positioning light shielding member MM, which has three openings M1 
through M3, between field lenses L01 through L03 and re-imaging lens L 
such that only the light fluxes to be used pass therethrough. 
Referring now to FIGS. 5A-5C, there is illustrated the arrangement of 
harmful light shielding member MM in the state when the focus detection 
apparatus cited in Japanese Patent Publication No. 63-289513 is mounted in 
a camera. When the focus detection apparatus is mounted in a camera, in 
order that the camera does not become too large, deflection mirror M is 
arranged between field lenses L01 through L03 (not shown) and re-imaging 
lens L, and generally the space within the camera is effectively used by 
bending or deflecting the light fluxes to be used in a direction that is 
nearly at a right angle to the photographic lens. In the aforementioned 
Japanese Patent Publication No. 63-289513, light shielding member MM is 
positioned at a right angle to the optical axis of the light fluxes to be 
used at position h between re-imaging lens L and deflection mirror M, or 
it is positioned by affixing it on the surface of bending mirror M. 
On the other hand, Japanese Patent Publication No. 62-189415 proposes a 
multi-area focus detection apparatus that provides focus detecting areas 
off the optical axis not only to the left and right, but also above and 
below. The arrangement of these areas is indicated in FIG. 6. Off-axial 
areas d and e are added to a central area on the optical axis and are 
positioned above and below the optical axis. Off-axial areas b and c are 
added to the left and right of the optical axis. Areas d and e are 
parallel with a central area on the optical axis, and are areas that are 
extended horizontally on the focal plane. Moreover, if this area 
arrangement is developed a little more, as shown in FIG. 7, a cross shape 
could be used for the central area on the optical axis which has a high 
frequency of use so that focus detection is possible whether the subject 
is horizontal or vertical. 
Referring now to FIG. 8, therein depicted is a cross-sectional diagram of a 
focal point detection optical system having the kind of multi-focus areas 
shown in FIG. 7. The elements that are arranged when mounted in a camera 
are indicated in the same manner as above. FIG. 8 demonstrates the focus 
detection state (view finder observation state), and the state wherein 
light fluxes that pass through the photographic lens are separated by 
semi-transparent main mirror M1 into light fluxes 21 for view finder 
observation and light fluxes 22 through 24 to be used. Observational light 
flux 21 is reflected in the direction of focusing screen S by main mirror 
M1, and light fluxes 22 through 24 to be used pass through main mirror M1 
and are bent and/or deflected in a direction of mirror box bottom surface 
B by fully reflective sub-mirror M2. The two mirrors M1 and M2 are 
supported by mirror holders 1 and 2 which are configured to have 
rotational operation by which they spring up and around their respective 
rotational axes (not shown in the figure) in order to capture or avoid the 
photographic light fluxes depending on the camera sequence. 
Provided on main mirror holder 1 is opening 1-1 which leads light fluxes 22 
through 24 to be used that have passed through main mirror M1 to 
sub-mirror M2. The basic composition of the focus detection optical system 
of FIG. 8 is nearly the same as is depicted in FIG. 5. That is, light 
fluxes 22 through 24 to be used pass through field mask 3 and field lens 5 
and are deflected in the direction of the photographic lens by deflection 
mirror Mo. Thereafter, the fluxes pass through aperture mask 6 and 
re-imaging lens 7 to arrive at CCD line sensor 8. Moreover, infrared cut 
filter 4 used for the purpose of compensating the comparative visual 
sensitivity of CCD line sensor 8 is positioned directly before field lens 
5. The aforementioned structures are fixed in their respective positions 
in focus detection holder 9, and taken as a whole they constitute the 
focus detection module. 
As previously described, because there are off-axial areas above and below 
the optical axis on focal plane, corresponding to each area there are 
three focus detection optical systems that are situated on the cross 
section which includes optical axis 20 of the photographic lens and the 
optical axis of light fluxes 22 through 24 to be used. Re-imaging lens 7 
has a total of two sets of lenses: because there are areas that are 
extended horizontally, one set of lenses 7-2 and 7-3, which correspond to 
areas off the optical axis, are perpendicular to the cross section of the 
diagram; and because one area has a cross shape, one set of lenses 7-1, 
which corresponds to the central area on the optical axis, is 
perpendicular and parallel to the cross section of the diagram. 
Attention is now paid to the harmful light that is produced and that causes 
harm to focus detection, in a multi-area focus detection optical system 
which incorporates the above-mentioned structures. First, light rays, 
which pass through opening 3-1 of field mask 3 and field lens 5-1 
corresponding to the central area on the optical axis but which are 
incident on re-imaging lenses 7-2 and 7-3 corresponding to the off-axial 
areas above and below the optical axis, are represented by reference 
numerals 25 and 26 which are indicated by dotted lines in FIG. 8. As 
illustrated in Japanese Patent Publication No. 63-289513, to shade these 
harmful light rays 25 and 26 before they are incident on re-imaging lens 
7, light shielding member 10, which has three openings through which light 
fluxes 22 through 24 to be used may pass, can be positioned between 
deflection mirror Mo and re-imaging lens 7. 
The problems of the aforementioned structures which are addressed by the 
present invention are described in regard to FIG. 8. The harmful light, 
which passes through openings 3-2 and 3-3 of field mask 3 and field lenses 
5-2 and 5-3 corresponding to the off-axial area above and below the 
optical axis but which is incident on re-imaging lens 7-1 corresponding to 
the central area on the optical axis, is represented by reference numerals 
27 and 28 which are indicated by the dotted lines in FIG. 9. 
Harmful light rays 27 and 28 have already doubled up with light fluxes 22 
through 24 to be used as indicated by the solid lines between deflection 
mirror Mo and re-imaging lens 7. When attempting to shade such harmful 
light at the position indicated by h, the light fluxes to be used are also 
shaded, thereby making it impossible to shade only the harmful light. 
Moreover, even if the shade member is affixed to the surface of deflection 
mirror Mo, the range in which harmful light 27 and 28 are reflected is 
doubled up in the range in which light fluxes 22 through 24 to be used are 
reflected at the surface of deflection mirror Mo. As such, it is not 
possible to completely shade only the harmful light. Such doubling up of 
harmful light fluxes with the light fluxes to be used of the central area 
on the optical axis easily occurs when the central area on the optical 
axis is a cross shape, and the width of the light flux 22 to be used of 
the central area on the optical axis in the cross sectional direction of 
FIG. 5 is large. 
Moreover, it is still not possible to shade only the harmful light at a 
position between field lens 5 and deflection mirror Mo because the 
position comes immediately after field lens 5 and light fluxes 22 through 
24 to be used and harmful light 27 and 28 are barely separate. 
Other known methods try to shield harmful light 27 and 28 before they are 
incident on the focus detection module. Harmful light 27 is light that 
enters from an area between shutter T and end M2a of sub-mirror M2. 
Because focusing screen plate S is not positioned above this area, them is 
almost no reverse incident light from the view finder eye piece that falls 
between sub-mirror M2 and shutter T. Moreover, even if the aforementioned 
space were little and if end 2a of the sub-mirror holder is extended 
beyond sub-mirror M2 as shown in FIG. 8, and made to have an extremely 
small gap with shutter T, it is possible to almost totally prevent light 
from being incident on field lens 7-2. Consequently, harmful light 27 can 
be shaded prior to falling on the focal point detection module. 
However, when it comes to harmful light 28, this is light that passes 
through the semi-transparent main mirror M1 at a place beyond end M2b on 
the photographic lens side of sub-mirror M2, and which comes through 
opening 1-1 of main mirror holder 1. Among the reverse incident light rays 
from the view finder eye piece, this is light that passes nearly straight 
through the center of focusing screen S. Such light is the strongest part 
of the reverse incident light and cannot be shaded at the focusing screen 
part or the main mirror part because the parts through which this reverse 
incident light comes, namely the semi-transparent part of main mirror M1 
and the opening part 1-1 of main mirror holder 1, am also the parts 
through which light flux 23 passes in order to be used, 
Consequently, there is a problem in multi-area focus detection optical 
systems which have off-axial focus detecting areas on a focal plane above 
and below the optical axis. In particular, such multi-area focus detection 
optical systems often allow harmful light to pass through a main mirror by 
passing through the center of the focusing screen plate from the view 
finder eye piece. Such harmful light that is incident upon the focus 
detection module cannot be prevented by inserting a planar shade member 
which has opening parts for only the number of light fluxes to be used 
either prior to becoming incident on the focus detection module or between 
the field lens and the re-imaging lens in the focus detection module as is 
proposed in Japanese Patent Publication No. 63-289513. 
The present invention takes the above-mentioned problems into 
consideration, and has the purpose of offering a focus detection apparatus 
that can effectively shade the harmful light of a multi-area focus 
detection apparatus that has off-axial focus detecting areas above and 
below the optical axis using an apparatus that can be adapted to be 
mounted in a camera, etc. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the above-mentioned 
problems of the known focus detection apparatuses. 
It is yet a further object of the present invention to provide a focus 
detection apparatus that effectively manages harmful light by efficiently 
using space near a deflection mirror maintained in a camera having a 
multi-area focus detection apparatus. 
These and other objects of the present invention are achieved by a focus 
detection apparatus adapted to reform images of light fluxes that pass 
through differing regions of a photographic lens into a pair of images on 
light receiving element arrays by using, for each pair of images, a field 
mask, a field lens, a pair of re-imaging lenses, and an aperture mask 
having a pair of aperture openings provided in the vicinity of the pair of 
re-imaging lenses. The focus detection apparatus has multiple focus 
detection blocks that detect the focus condition of the photographic lens 
from positions relative to the pairs of images. Additionally, the focus 
detection apparatus is further adapted to detect the focus condition of 
multiple areas on an focal plane. The focus detection apparatus comprises 
a deflection mirror positioned between the field lens and the pair of 
re-imaging lenses. The deflection mirror causes the light fluxes to be 
deflected at nearly right angles for focus detection. Finally, a light 
shielding member is positioned in a triangular space determined by a beam 
of light that is closest to the pair of re-imaging lenses, a beam of light 
that is closest to the field lens and a reflecting surface of the 
deflection mirror,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the present preferred embodiments 
of the present invention, examples of which are illustrated in the 
accompanying drawings, wherein like reference numerals refer to like 
elements throughout. 
A first embodiment of a focus detection apparatus according to the present 
invention is shown and described with reference to FIGS. 1 and 2. In FIGS. 
1 and 2, references are made to pads which correspond to the parts of the 
prior art focus detecting apparatus depicted in FIG, 9, and, as such, a 
redundant, second explanation of such parts will be omitted. 
In order to prevent the incidence of harmful light 28 on re-imaging lens 7 
of the central area on the optical axis, light shielding member 12 is 
arranged in space U which has a triangular cross-sectional shape 
determined by reflective plane 30 of deflection mirror Mo. Light beam 23a 
is the light flux 23 to be used that is closest to re-imaging lens 7, and 
light beam 24-1a is the light flux 24 to be used that faces re-imaging 
lens 7 from deflection mirror Mo and is closest to field lens 5. 
The orientation of light shielding member 12 is nearly parallel to field 
mask 3. Moreover, the size to the left and the right in the diagram shall 
be width n which is restricted between light fluxes 22 and 23 to be used 
and which reaches from field lens 5 to deflection mirror Mo. The position 
up and down in the diagram is between light fluxes 24-1 and 22-1 
(reflected light of light flux 22) to be used which reaches between 
deflection mirror Mo to re-imaging lens 7. There is no need to provide 
light shielding member 12 at a position outside of the light flux 24 since 
light flux 22 to be used reaches from field lens 5 to deflection mirror Mo 
because with deflection mirror Mo there is extremely little space and 
there is no relationship to harmful light 28 which is to be shaded, By 
making light shielding member 12 have the aforementioned width in its 
position, only the harmful light is shaded without shading either the 
light flux to be used heading from field lens 5 to deflection mirror Mo or 
the light flux to be used heading from deflection mirror Mo to re-imaging 
lens 7. 
Moreover, as shown in FIG. 2, the planar shape of light shielding member 12 
need only be of width n to fit between light fluxes 22 and 23 to be used. 
If made into an H shape by taking away the areas which have no 
relationship with light flux and fixed to focus detection holder 9 at ends 
12a and 12b, a light shielding member of width n can be held between the 
two light fluxes 22 and 23. Moreover, as shown in FIGS. 5A-5C and 6, if a 
focus detecting area is provided to the right and left of the central area 
on the optical axis, the light fluxes of the right and left areas come to 
positions like 22S and 22L, and wide parts 12S and 12L of light shielding 
member 12 can maintain the function of shading the harmful light between 
the left and right areas. 
Referring now to FIG. 3, therein depicted is a cross section of a second 
embodiment of a focus detection apparatus according to the present 
invention. Having the same general location and width as the first 
embodiment, light shielding member 13 shades harmful light 28 and is 
arranged to face roughly parallel with deflection mirror Mo. When oriented 
this way, light shielding member 13 can certainly shield harmful light 28, 
but among the light fluxes reflected by deflection mirror Mo and facing 
re-imaging lens 7, light shielding member 13 can simultaneously shade 
reflected light 26-1 of harmful light 26 as shown in FIG. 3. In 
particular, by orienting light shielding member 13 such that it has a 
position in a direction substantially parallel to deflection mirror Mo and 
to an angle less than a right angle to aperture mask 6, light shielding 
member 13 can simultaneously function to shield light coming from field 
lens 3 and the harmful light reflected off of deflection mirror Mo. 
Consequently, it is possible to prevent harmful light 26 at the same time 
that light shielding member 13 prevents harmful light 28. 
Light shielding member 10 (FIG. 8) has the purpose of preventing harmful 
light 25 and 26. The part of light shielding member 10 that has the 
purpose of shading harmful light 26 may be made smaller or even omitted 
from the structure depicted in FIG. 3. Additionally, the planar shape of 
light shielding member 13 and the method of holding it are the same as in 
the first embodiment. 
The embodiments described above illustrate that it is possible to prevent 
harmful light in a focus detection apparatus disposed in a multi-area 
focus detection apparatus having off-axial focus detecting areas above and 
below an optical axis in addition to the center of an imaging area, of a 
camera's photo-optical system. The present invention prevents harmful 
incident light that is incident upon a re-imaging lens of a central area 
from the field lens of the off-axial area below the optical axis and which 
is naturally produced by the focus detection apparatus having an off-axial 
area below the optical axis. Such advantages are realized by effectively 
arranging a light shielding member in the space of the triangular 
cross-sectional shape that is formed by the most exterior light beams of 
the light fluxes to be used and the reflective surface of a deflection 
mirror when mounted in a camera. Such a triangular space may be found in a 
camera having a deflection mirror arranged between a field lens and a 
re-imaging lens. 
Also, the present invention has the effect that the number of harmful light 
shielding members can be reduced since shade members can be appropriately 
directed and shaped. As such, shade members can shade not only the 
aforementioned harmful light, but simultaneously shade the harmful light 
that is incident on a re-imaging lens of an off-axial area above and below 
the optical axis coming from the field lens of the central area. If there 
is an off-axial area to the right and left of the optical axis, all or 
part of the harmful light produced between the central area and the 
off-axial area to the right and left of the optical axis can be shaded. 
Although a few preferred embodiments of the present invention have been 
shown and described, it would be appreciated by those skilled in the art 
that changes may be made in these embodiments without departing from the 
principles and spirit of the invention the scope of which is defined in 
the claims and equivalents thereof.