Pupil divisional focusing position detection apparatus using lenticula lens

In a focusing position detection apparatus for detecting a focusing position by causing rays of light coming from a peripheral portion of an exit pupil of a photographing lens to enter a pair of self-scanning type photoelectric element arrays through a lenticular lens group and then detecting the difference of the phases of the output signals from the photoelectric element arrays, in order to cause the rays of light to enter accurately the pair of self-scanning type photoelectric element arrays, a pitch Po between photoelectric elements which constitute the pair of photoelectric element arrays is suitably changed relative to a pitch P between small lens element which constitute the lenticular lens group, and furthermore, in order to detect the focusing position accurately, the boundary areas in the convex surfaces of the small lens elements of the lenticular lens group are made opaque so that noises in the output signals of the photoelectric element arrays are reduced.

BACKGROUND OF THE INVENTION 
The present invention relates to an electronic focusing position detection 
apparatus for detecting a focusing position in cameras and the like. 
Conventionally, there is known a focusing position detection apparatus 
utilizing a photoelectric element whose resistance becomes maximum when 
the image of an object is focused on the photoelectric element. In another 
conventional focusing position detection apparatus, double images of the 
object are respectively projected onto different photoelectric elements 
and the difference between the electric currents which flow through the 
respective photoelectric element is measured and when the image of the 
object is focused, the difference of the photoelectric currents becomes 
minimum. 
In these focusing position detection apparatuses, the focusing position 
itself can be determined. However, when the object is out of focus, it 
cannot be determined whether the focused position is in front of the film 
surface (hereafter referred to as a front focusing state) or the focused 
position is behind the film surface (referred to as a back focusing 
state). Therefore, in these apparatuses, it is required that a prescanning 
be initiated from a predetermined direction, for example, from close range 
to infinite range so that the focusing position is searched and detected 
and then the photographing lens is moved to the detected focusing 
position. This prescanning step, however, is laborious. 
Furthermore, in this type of the focusing position detection apparatuses a 
lenticular lens group consisting of a number of small lens elements is 
used and the small lens elements are adjacent each other and are made 
integrally, and near the boundary areas of a convex surface of each small 
lens element, each lens element has a radius of curvature which is 
different from a predetermined radius of curvature or has a reversed 
radius of curvature in a certain range. Therefore, although all the rays 
of light which enter one small lens element have to enter its counterpart 
photoelectric element, some of the rays of light are refracted in the 
boundary areas in different directions and enter the other photoelectric 
elements, so that noises are produced in the output signals from the 
photoelectric elements. As a result, the exact focusing position cannot be 
detected. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a focusing position detection 
apparatus which does not require a laborious prescanning step for 
searching and detecting the focusing position. 
Another object of the invention is to provide a focusing position detection 
apparatus capable of performing the focusing detection accurately by 
preventing the rays of light from passing through the boundary areas in 
the convex surfaces of the small lens elements of a lenticular lens group 
having photoelectric element arrays for detecting the focusing position. 
According to the invention, a focusing position is detected by causing rays 
of light from a peripheral portion of an exit pupil of a photographing 
lens to enter a pair of self-scanning type photoelectric element arrays 
through a lenticular lens group and then detecting the difference of the 
phases of the output signals from the photoelectric element arrays, and 
the pitch Po between photoelectric elements which constitute the pair of 
photoelectric element arrays or the pitch P between small lens elements 
which constitute the lenticular lens group is determined so as to maintain 
a relationship of Po=W P/D, wherein D is the distance between the exit 
pupil of the photographing lens and the center of curvature of a small 
lens element on the optical axis of the photographing lens, and W is the 
distance between the center of curvature of the small lens element on the 
optical axis and a plane on which the photoelectric element arrays are 
disposed. 
Furthermore, according to the invention, the boundary areas of the convex 
lens surfaces of the lenticular lens group are made opaque by filling in 
or applying a light absorbing material to the boundary areas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is schematically shown a focusing state of a 
pupil divisional type focusing position detection apparatus to which the 
invention can be applied. 
As shown in FIG. 1, rays of light are caused to enter a pair of 
self-scanning type photoelectric element arrays 3, such as CCD (Charge 
Coupled Device) type image sensors and MOS type image sensors, from a 
peripheral portion of an exit pupil of a photographing lens 1 through a 
group of small lenses or a lenticular lens group 2, such as lenticular 
lenses, so that the focusing position is detected from the difference of 
the phases of the output signals of the photoelectric element arrays 3. 
This type of the focusing position detection apparatus is referred to as a 
pupil divisional type focusing position detection apparatus since rays of 
light coming from two-divided portions of a photographing lens are 
utilized in detecting the focusing position. The focusing position is 
detected as follows: When the image of an object is in the focusing state 
as shown in FIG. 1, the divisional rays of light correctly enter a pair of 
photoelectric elements 3a-1 and 3a-2 from the photographic lens 1. 
Therefore, the phases of the outputs of the respective photoelectric 
elements 3a-1, 3a-2 are in agreement with each other. When the image is 
focused in front of the focusing plane, that is, in the so-called front 
focusing state, the divisional rays of light from the photographing lens 1 
respectively enter another pair of photoelectric elements 3b-1, 3c-2, so 
that the phases of the output signals of the pair of the photoelectric 
elements 3b-1, 3c-2 are shifted from each other as shown in FIG. 4. On the 
other hand, in the case of a back focusing state as shown in FIG. 5, a 
divisional rays of light l.sub.1 enters a photoelectric element 3c-2, 
which is indicated by a blank block, although, in the focusing state, the 
divisional rays of light l.sub.1 should enter the photoelectric element 
3a-1, which is indicated by a solid black block in FIG. 5. Furthermore, in 
the back focusing state, another divisional ray of light l.sub.2 enters 
the photoelectric element 3b-1, which is indicated by a solid black block. 
As a result, the phases of the output signals of the photoelectric 
elements 3c-2, 3b-1 are reversed as shown in FIG. 6 in contrast with the 
case in FIG. 4. Thus, by detecting the difference of the phases of the 
output signals of the photoelectric elements, it can be determined whether 
the image of an object is in the focusing state, in the front focusing 
state or in the back focusing state. 
In this type of the focusing position detection apparatus, each pair of 
photoelectric elements 3a, 3b, . . . is disposed so as to correspond with 
each lens element which constitutes a lenticular lens group 2. Therefore, 
a pitch Po between each pair of photoelectric elements is equal to a pitch 
P between the lens elements. In this construction, the rays of light, 
l.sub.1 and l.sub.2, which come from points h and i on the exit pupil 
plane G of the photographing lens 1 converge on the optical axis S of the 
photographing lens 1 (FIGS. 7, 8) and enter a pair of photoelectric 
elements 3a corresponding to a small lens element 2a. However, rays of 
light which deviate from the optical axis S, for example, l.sub.3 and 
l.sub.4, do not enter any of a pair of photoelectric elements 3m 
corresponding to a small lens element 2m. Furthermore, in contrast with 
the rays of light l.sub.1 and l.sub.3, rays of light l.sub.5 and l.sub.6, 
enter in reverse order one of a pair of photoelectric elements 3v 
corresponding to small lens element 2v and one of a pair of photoelectric 
elements 3w corresponding to a small lens element 2w, which is located 
adjacent the one photoelectric element 3v. Thus, the focusing position to 
be indicated by each pair of the photoelectric elements becomes more 
inaccurate as it goes away from the optical axis S. 
In the invention, in order that rays of light, l.sub.1 -l.sub.6, coming 
from points h and i on the exit pupil plane G of the photographing lens 1 
enter correctly their corresponding pairs of photoelectric elements, the 
pitch Po between the photoelectric element pairs is suitably changed 
relative to the pitch P between the small lens elements, so that each pair 
of the photoelectric elements is apparently made not to correspond to each 
lens element except that on the optical axis S. However, each pair of the 
photoelectric elements comes to substantially correspond to each lens 
element with respect to the neutral lines of the rays of light from the 
points h and i on the exit pupil plane G, for example, neutral lines 
S.sub.1 and S.sub.2 in FIG. 8. 
The pitch Po between the photoelectric elements is determined as follows: 
Referring to FIG. 9, the exit pupil plane G of the photographing lens 1 
and the optical axis S of the photographing lens 1 intersect at M, and the 
distance along the optical axis S between the exit pupil plane G and the 
center of curvature O of each lens element of the lenticular lens group 2 
is D, and the distance along the optical axis S between the center of 
curvature O and an attachment plane F for attaching each pair of the 
photoelectric elements thereto is W. 
In a construction using the lenticular lens group 2 with its convex side 
directed to the photographing lens 2, the photoelectric element attachment 
plane F is on the back side of the lenticular lens group 2 and therefore 
the distance W is equal to T-R, wherein T is the thickness of the 
lenticular lens group and R is the radius of curvature of each lens 
element of the lenticular lens group 2. 
When the center of curvature of a n th small lens element 2n counted from 
the optical axis S is O.sub.n and the distance between the optical axis S 
and the center of curvature O.sub.n is L.sub.n, and A.sub.n is a cross 
point of a neutral line MO.sub.n and the attachment plane F, that is, the 
center of a pair of the photoelectric elements which belong to the small 
lens element 2n, and B.sub.n is a cross point of the attachment plane F 
and a pitch line with respect to the small lens element 2.sub.n, that is, 
a line parallel to the optical axis S, which passes through the center of 
curvature O.sub.n, the distance X.sub.n between the point A.sub.n and the 
point B.sub.n is represented as follows: 
##EQU1## 
X.sub.n is the summation of the variation of the pitch Po between the 
pairs of the photoelectric elements corresponding to the summation of the 
pitch P between the small lens elements in the range from the optical axis 
S to the small lens element 2.sub.n. A summation X.sub.m of the variation 
of the pitch Po between the pairs of the photoelectric elements up to a 
small lens element 2.sub.m, which is located adjacent the small lens 
element 2.sub.n and nearer the optical axis S, is represented as follows: 
##EQU2## 
Therefore, the change .DELTA.X of the pitch Po of the pair of the 
photoelectric elements corresponding to the one pitch between the small 
lens elements is 
##EQU3## 
Therefore, the pitch Po between the photoelectric elements is 
##EQU4## 
As mentioned previously, since W=T-R, Equation (4) can be rewritten as 
follows: 
##EQU5## 
By determining the pitch Po between the photoelectric elements in 
accordance with the thus determined pitch Po, the rays of light from each 
divided area of the photographing lens 1 correctly enter the corresponding 
pairs of photoelectric elements, so that the correct output signals are 
produced from the pairs of the photoelectric elements. 
Referring to FIG. 10, there is shown a construction in which the convex 
side of the lenticular lens group 2 is reversed with respect to the 
photographing lens 1. In this construction, the photoelectric element 
attachment surface F is located away from the surface of the lenticular 
lens group 2. However, when the distance D between the exit pupil plane G 
of the photographing lens 1 and the center of curvature O of each lens 
element of the lenticular lens group 2, the distance W from the center of 
curvature O to the photoelectric element attachment surface F and the 
other factors are set as in the case of FIG. 9, the relationship between 
the pitch Po between the photoelectric elements and the pitch P between 
the small lens elements can be represented by the same equation as 
Equation (4). 
Therefore, in this invention, the pitch Po between the photoelectric 
elements can be determined from a predetermined pitch P between the small 
lens elements and in reverse order, a pitch P can be determined from a 
predetermined pitch Po. This is useful when a photoelectric element pair 
array is made using a commercially available lenticular lens group and 
also when a lenticular lens group is made using a commercially available 
photoelectric element pair array. The lenticular lens group for use in 
this sort of the focusing position detection apparatus consists of a 
number of small lenses which are adjacent each other and are made 
integrally. As shown in FIG. 11, near the boundary areas of the convex 
surface of each lens element, the surface of each lens element has a 
radius of curvature which is different from the predetermined radius of 
curvature R or has a reversed radius of curvature in a width of Q. 
Therefore, although all the rays of light which enter the lens element 2a 
should enter the photoelectric element 3a-1, some of the rays of light are 
refracted in the boundary areas Q in different directions and enter the 
other photoelectric elements, producing noises in the output signals of 
the photoelectric elements and preventing the exact focusing position 
detection. 
This disadvantage can be prevented by making the boundary areas of the lens 
element opaque. For example, as shown in FIG. 12, a light absorbing 
material 4 is filled in or applied to the valley portions which constitute 
the boundary areas Q. As the light absorbing material 4, for example, an 
epoxy resin with carbon black dispersed therein can be employed. When the 
light absorbing material 4 is filled in or applied to the valley portions, 
it must be noted that the other portions of the lens surfaces are not 
smeared by the light absorbing material 4. In order to fill the light 
absorbing material 4 more securely, grooves for filling the light 
absorbing material 4 therein can be formed in the valley portions in the 
areas Q. 
By making the boundary areas Q opaque or light absorbing, the travelling of 
the rays of light which reach the boundary areas Q is stopped so that 
generation of the noise signals is prevented. 
In this type of the focusing position detection apparatus, the lenticular 
lens group 2 can be disposed so as to be away from the photoelectric 
element array 3, with the convex surfaces of the lens group 2 directed to 
the photoelectric element arrays 3. In this case, the same disadvantage 
occurs. Namely, although all the rays of light coming from the lens 
element 2a should enter the corresponding photoelectric element 3a-1, the 
rays of light coming from the boundary areas Q enter other photoelectric 
elements, so that the focusing position detection cannot be performed 
accurately. This disadvantage can also be prevented by filling in or 
applying the light absorbing material 4 to the valley portions in the 
boundary areas Q to make the boundary areas Q opaque.