Focusing apparatus

Claim 2

A focusing apparatus for an image forming optical system comprising: a plurality of series-connected photoelectric elements, each having a constant-current characteristic with respect to the impedance of its respective load arranged to receive by their light receiving faces parts of a real image formed by said optical system, an electric system for detecting output signals from said series connection of photoelectric elements under the condition that both ends of said series connection have essentially a zero potential difference therebetween; and means, responsive to the said output signals, detected by said electric system, for adjusting said optical system in a manner to maintain the current output of said series-connected elements at a minimum value.

Claim 3

A focusing apparatus as defined in claim 1, wherein said electric system comprises: an operational amplfier for detecting and amplifying output signals of said series-connected elements under said condition, and wherein said means for causing the current output of said series-connected elements to be at a minimum value comprises comprising an electric servomechanism operatively linked to said optical system, and operatively connected to said oPerational amplifier.

Claim 4

A focusing apparatus as defined in claim 2, wherein said image forming optical system is an objective lens of a photographic camera, and said photoelectric elements are arranged in the camera so as to receive parts of said real image which correspond to a real image to be projected on a photographic film in the camera.

Claim 5

A focusing apparatus as defined in claim 2, wherein said image forming optical system is a projection lens of a picture projector, said projector having a half-mirror in a light path of the apparatus so that a light beam reflected from the projected picture on a screen forms a real image on said light-receiving face of the elements.

Claim 6

A focusing apparatus for an image-forming optical system comprising: a group of photoelectric elements each having a constant-current characteristic with respect to the impedance of its respective load arranged to receive by their light receiving faces parts of a real image formed by said optical system, a switching network which alternatively changes the connection of said elements between a series connection and parallel connection, amplifier means for detecting and amplifying output signals from said connection of photoelectric elements, a comparator having two input terminals, a switch which repeatedly changes over in synchronism with said switching network so as to apply the output of said amplifier means to one input terminal of said comparator during series connection of said elements and to feed the output of said amplifier means to the other input terminal of said comparator during parallel connection of said elements, said comparator serving to compare the two outputs of said amplifier means corresponding respectively to said series connection and said parallel connection and to generate an output proportional to the difference between said two outputs, and an electric servomechanism operatively linked to said optical system, and operatively connected to the output terminal of said comparator in such a manner that the servomechanism stops upon detecting the maximum value of said output of the comparator.

Claim 7

A focusing apparatus for an image-forming optical system comprising: a group of photoelectric elements each having a constant-current characteristic with respect to the impedance of its respective load arranged to receive by their light receiving faces parts of a real image formed by said optical system, a switching network which alternatively changes the connection of said elements between a series connection and parallel connection, amplifier means for detecting and amplifying output signals from said connection of photoelectric elements, a comparator having two input terminals, a switch which repeatedly changes over in synchronism with said switching network so as to apply the output of said amplifier means to one input terminal of said comparator during series connection of said elements and to feed the output of said amplifier means to the other input terminal of said comparator during parallel connection of said elements, said comparator serving to compare the two outputs of said amplifier means corresponding respectively to said series connection and said parallel connection and to generate an output proportional to the difference between said two outputs, and an electric servomechanism operatively linked to said optical system, and operatively connected to the output terminal of said comparator in such a manner that the servomechanism stops upon detecting the maximum value of said output of the comparator.

Claim 8

A focusing apparatus as defined in claim 5, wherein said amplifier means is as operational amplifier.

Claim 9

A light measuring system for detecting a focusing condition at the focal plane of an image- forming optical system, said system comprising: a plurality of photoelectric elements connected in series with one another, each of said photoelectric elements having a constant-current characteristic with respect to the impedance of a respective load therefor, arranged to receive, at their light receiving faces, portions of a real image formed by said optical system; and means for detecting output signals from said series connection of photoelectric elements under the condition that both ends of said series connection have essentially a zero potential difference therebetween, and wherein said means comprises an operational amplifier for detecting and amplifying the output signals of the photoelectric elements connected in series and means for causing the current output of the photoelectric elements to be at a minimum value.

Claim 10

A light measuring system for detecting a focusing condition at the focal plane of an image- forming optical system, said system comprising: a plurality of photoelectric elements connected in series with one another, each of said photoelectric elements having a constant-current characteristic with respect to the impedance of a respective load therefor, arranged to receive, at their light receiving faces, portions of a real image formed by said optical system; and means for detecting output signals from said series connection of photoelectric elements under the condition that both ends of said series connection have essentially a zero potential difference therebetween, and wherein said means comprises an operational amplifier for detecting and amplifying the output signals of the photoelectric elements connected in series and means for causing the current output of the photoelectric elements to be at a minimum value.

Claim 11

A device according to claim 7, and further including an electric servomechanism operatively linked to said optical system and connected to said operational amplifier.

Claim 12

A device according to claim 8, wherein said image forming optical system comprises an objective lens of a photographic camera, and said photoelectric elements are arranged in the camera, so as to receive portions of a real image which correspond to a real image to be projected on a photographic film in the camera.

Claim 13

A device according to claim 8, wherein said image forming optical system comprises a projection lens of a picture projector, said projector having a half-mirror provided in a light path of the system, so that a light beam reflected from the projected picture on a screen forms a real image on the light receiving face Of the photoelectric elements.