Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
2002-12-27
2004-03-23
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C396S106000, C356S003040
Reexamination Certificate
active
06711352
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical range finder incorporated in a camera or the like to be used for automatic focus adjustment. More specifically, the invention relates to a technology for obtaining measurement accuracy by making distance determination multistage. The invention also relates to a multistage determination process or algorithm. In addition, the invention relates to a light quantity calibration technology.
FIG. 12
is a schematic perspective view showing an example of a camera incorporating a conventional optical range finder. A camera
25
is provided with a lens barrel
27
on a front of a body
26
. The optical range finder composed of a projection unit
1
and a photoreceiving unit
2
is mounted to the body
26
. The projection unit
1
projects optical flux to an object located in an optical axis direction. The photoreceiving unit
2
receives the optical flux returned from the object, and outputs a detection signal in accordance with a light quantity of the received optical flux. The optical range finder determines a distance to the object based on the detection signal outputted from the photoreceiving unit
2
, and executes ranging by using a relation that a reflected light quantity from the object is inversely proportional to a square of the distance.
FIG. 13
is a schematic view showing a specific constitution of the conventional optical range finder. The projection unit
1
and the photoreceiving unit
2
are assembled into a holding frame
30
. This holding frame
30
is supported on a circuit board
4
a
. The circuit board
4
a
is attached in the body
26
of the camera
25
shown in FIG.
12
. The projection unit
1
is constituted of a projection lens
1
b
mounted to a front of the holding frame
30
, and a light emitting element
1
a
for emitting optical flux such as infrared rays to the lens
1
b
. On the other hand, the photoreceiving unit
2
is constituted of a lens
2
b
mounted to the front of the holding frame
30
to converge the optical flux returned from the object, and a light detecting element
2
a
arranged oppositely to the lens
2
b
. The light detecting element
2
a
outputs a detection signal having a current amount in accordance with the received light quantity. A circuitry unit assembled in the circuit board
4
a
processes the detection signal to execute ranging.
The optical range finder of the light quantity type is simple in structure compared with a range finder based on a principle of triangulation. Accordingly, in the conventional optical range finder, a binary system for determining a distance in two stages, i.e., far and short distance zones, is often used. That is, the circuitry unit of the optical range finder is provided with a comparator for comparing the detection signal with a predetermined reference level to determine whether the object is located in a far distance side or a short distance side. As the optical range finder executes ranging based on a light quantity reflected from the object, accuracy is not so high because of factors described below, and it has been considered improper to increase accuracy from the conventional two-stage determination to multistage determination of three stages or more. As the light quantity depends on a reflectance of the object (target of the camera or the like), measurement accuracy cannot be obtained, and it has been considered meaningless to set multiple stages. In addition, circuitry needs only one comparator in the case of binary determination, and is very simple, and importance has been placed on practical rationality. For a request of setting of multiple stages, a system based on a normal triangular ranging system is suited, and there has been no point in setting multiple stages in the optical range finder of the light quantity type.
However, following recent diversification of cameras, low cost and miniaturization have been requested of the range finder used for automatic focus adjustment or the like. Thus, there has been a demand for setting multiple stages in the optical range finder of the light quantity type, which is advantageous in cost and size. The present invention proposes setting of multiple stages in the optical range finder of the light quantity type.
In the case of executing determination of the light quantity reflected from the object in multiple stages, a complicated system might be employed, which prepares a plurality of determination circuits in accordance with the number of stages, and a plurality of reference levels in accordance with a variable light quantity. Alternatively, means may be employed, which directly measures a level of a reflected light quantity and converts it into numerical value data, and calculates object distance information based on a physical relation between the distance and the light quantity. However, the above-described measures both result in complex circuitry, and thus they are not suitable for the optical range finder which should be simple ranging means. In a general purpose optical range finder, simple determination of far and near stages is executed, the number of reference levels is one, and a circuit is very simple. In the market, there is a demand for means making the optical range finder multistage without complicating circuitry, which is now a problem to be solved. In this case, a process or algorithm of multistage determination is also a problem to be solved. In addition, if the optical range finder of the light quantity type is made multistage, ranging accuracy becomes higher than the conventional bi-stage type and, accordingly, error factors must be suppressed. In such a case, it is considered effective to execute calibration of a light quantity of projected beam beforehand, which is also a problem to be solved.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems of the prior art, first means has been contrived. That is, the present invention is directed to an optical range finder having a projection unit for projecting optical flux to an object, a photoreceiving unit for receiving the optical flux returned from the object and outputting a detection signal in accordance with a light quantity of the received optical flux, and a circuitry unit for conducting a measurement of a distance to the object based on the detection signal, wherein the circuitry unit comprises a light quantity determination circuit for comparing a signal level of the detection signal with a reference level to carry out binary determination of the light quantity of the returned optical flux, a reference level setting circuit for switchably supplying a plurality of reference levels to the light quantity determination circuit, the reference levels being preset in correspondence to multiple stages of the distance, and a control circuit for controlling the reference level setting circuit to supply the reference levels while switching the reference levels so as to enable the light quantity determination circuit to execute a plurality of the binary determination with the supplied reference levels for one measurement, thereby specifying the distance to one of the multiple stages based on the thus obtained plurality of the binary determination.
Preferably, the reference level setting circuit sets the reference levels in correspondence to the multiple stages of the distance where inverse numbers of the distance of the multiple stages are arranged in an arithmetic series. For example, the reference level setting circuit sets the reference levels in correspondence to the multiple stages of the distance where the distance is divided into the multiple stages based on a harmonic sequence (1/2, 1/3 . . . 1
). Preferably, the reference level setting circuit comprises a plurality of current supplies arranged in parallel with each other to output different current amounts, the plurality of the current supplies being set so that the respective current amounts may be arranged in a geometric series where 2 is a base, and a switch for switchably combining the current supplies to generate a multiple of current a
Kohno Takanori
Kurosu Tomio
Nidec Copal Corporation
Nixon & Peabody LLP
Perkey W. B.
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