Method and apparatus for measuring and/or setting lens focus distance

Claim 2

Apparatus for setting the focus of a lens for a predetermined object distance, said apparatus comprising: means for defining a photosensitive surface having an electrical characteristic which locally varies in accordance with the intensity of illumination incident thereto and for providing an analog electrical signal that varies in a pedetermined sequence in accordance with the local value of said electrical characteristic of said photosensitive surface; means for mounting a lens, the focus of which is to be set, in a predetermined manner with respect to said photosensitive surface such that light emerging from the lens can impinge on said photosensitive surface and form thereon a pattern of illumination whose area varies in accordance with the state of focus of the lens; means for providing a source of illumination which is directed at the lens and effectively originates from the predetermined object distance for which the lens focus is to be set, said photosensitive surface, said mounting means, and said illumination source providing means being arranged with respect to one another so that the best focus of the lens for the predetermined object distance occurs when the area of the pattern of illumination formed by the lens on said photosensitive surface is smallest; and means for receiving said analog electrical signal and in response thereto providing an output response proportional to the size of the area of the pattern of illumination formed on said photosensitive surface so that the state of focus of the lens can be determined as the lens focus is adjusted.

Claim 3

The apparatus of claim 1 wherein said first stated means comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a pedetermined pattern and rate to provide said electrical signal.

Claim 4

The apparatus of claim 1 wherein said last stated means comprises: (a) clipping circuit means for receiving said electrical signal as an input and providing an output signal whose instantaneous value is limited to a predetermined level; and (b) a DC voltmeter arranged to receive said clipping circuit means output signal, said DC voltmeter being operative to time average said clipping circuit means output signal and display said value of said time averaged signal, said displayed value of said time averaged signal being proportional to the area of said pattern of illumination formed on said photosensitive surface.

Claim 5

The apparatus of claim 3 wherein said first stated means recited in claim 1 comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 6

The apparatus of claim 4 wherein said DC voltmeter is selected so as to have a frequency response that is slower than said predetermined rate at which said television camera tube photosensitive surface is scanned and said predetermined scanning rate is selected to be faster than the rate at which the lens focus is adjusted.

Claim 7

The apparatus of claim 1 wherein said illumination source providing means comprises a collimated point source directed at the lens.

Claim 8

Apparatus for determining the focal length of a lens, said apparatus comprising: means for defining a photosensitive surface having an electrical characteristic which locally varies in accordance with the intensity of illumination incident thereto and for providing an analog electrical signal that varies in a predetermined sequence in accordance with the local value of said electrical characteristic of said photosensitive surface; means for mounting a lens, the focal length of which is to be determined, in a predetermined manner with respect to said photosensitive surface so that the spacing between the lens and said photosensitive surface can be changed such that light emerging from the lens can impinge on said photosensitive surface and form thereon a pattern of illumination whose area varies in accordance with the spacing separating the lens and said photosensitive surface; means for providing a collimated source of illumination directed at the lens, said photosensitive surface, said mounting means, and said illumination source providing means being arranged with respect to one another so that the area of the pattern of illumination formed by the lens on said photosensitive surface is smallest when the lens and said photosensitive surface are separated by a distance related in a predetermined manner to the lens focal length; and means for receiving said analog electrical signal and in response thereto providing an output response proportional to the size of the area of the pattern of illumination formed on said photosensitive surface so that the focal length of the lens can be determined as the distance separating the lens and said photosensitive surface is adjusted.

Claim 9

Apparatus for determining the focal length of a lens, said apparatus comprising: means for defining a photosensitive surface having an electrical characteristic which locally varies in accordance with the intensity of illumination incident thereto and for providing an analog electrical signal that varies in a predetermined sequence in accordance with the local value of said electrical characteristic of said photosensitive surface; means for mounting a lens, the focal length of which is to be determined, in a predetermined manner with respect to said photosensitive surface so that the spacing between the lens and said photosensitive surface can be changed such that light emerging from the lens can impinge on said photosensitive surface and form thereon a pattern of illumination whose area varies in accordance with the spacing separating the lens and said photosensitive surface; means for providing a collimated source of illumination directed at the lens, said photosensitive surface, said mounting means, and said illumination source providing means being arranged with respect to one another so that the area of the pattern of illumination formed by the lens on said photosensitive surface is smallest when the lens and said photosensitive surface are separated by a distance related in a predetermined manner to the lens focal length; and means for receiving said analog electrical signal and in response thereto providing an output response proportional to the size of the area of the pattern of illumination formed on said photosensitive surface so that the focal length of the lens can be determined as the distance separating the lens and said photosensitive surface is adjusted.

Claim 10

The apparatus of claim 7 wherein said first stated means comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 11

The apparatus of claim 7 wherein said last stated means comprises: (a) clipping circuit means for receiving said electrical signal as an input and providing an output signal whose instantaneous value is limited to a predetermined level; and (b) a DC voltmeter arranged to receive said clipping circuit means output signal, said DC voltmeter being operative to time average said clipping circuit means output signal and display said value of said time averaged signal, said displayed value of said time averaged signal being proportional to the area of said pattern of illumination formed on said photosensitive surface.

Claim 12

The apparatus of claim 9 wherein said first stated means recited in claim 7 comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 13

The apparatus of claim 10 wherein said DC voltmeter is selected to have a frequency response that is slower than said predetermined rate at which said television camera tube photosensitive surface is scanned and said predetermined scanning rate is selected to be faster than the rate at which the lens is adjusted.

Claim 16

The method of claim 12 wherein the size of the area of illumination formed by the lens is measured by means for receiving said analog electrical signal and in response thereto providing an output response proportional to the area of the pattern of illumination formed on said photosensitive surface.

Claim 17

The method of claim 12 wherein said means for defining said photosensitive surface and providing said analog electrical signal comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 18

The method of claim 14 wherein said area measuring and output response providing means comprises: (a) clipping circuit means for receiving said electrical signal as an input and providing an output signal whose instantaneous value is limited to a predetermined level; and (b) a DC voltmeter arranged to receive said clipping circuit means output signal, said DC voltmeter being operative to time average said clipping circuit means output signal and display said value of said time averaged signal, said displayed value of said time averaged signal being proportional to the area of said pattern of illumination formed on said photosensitive surface.

Claim 19

The method of claim 15 wherein said means for defining said photosensitive surface and providing said analog electrical signal comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 20

The method of claim 16 wherein said DC voltmeter is selected to have a frequency response that is slower than said predetermined rate at which said television camera tube photosensitive surface is scanned and said predetermined scanning rate is selected to be faster than the rate at which the lens focus is adjusted.

Claim 21

The method of claim 12 wherein said illumination source directed at the lens comprises a collimated point surce.

Claim 24

The method of claim 19 wherein the size of the area of illumination formed by the lens is measured by means for receiving said analog electrical signal and in response thereto providing an output response proportional to the area of the pattern of illumination formed on said photosensitive surface.

Claim 25

The method of claim 19 wherein said means for defining said photosensitive surface and providing said analog electrical signal comprises a television camera tube which includes said photosensitive surface on which light emerging from the lens impinges to form thereon said pattern of illumination and electronic circuit means for scanning said photosensitive surface in a predetermined pattern and rate to provide said electrical signal.

Claim 26

The method of claim 21 wherein said area measuring and ouput response providing means comprises: (a) clipping circuit means for receiving said electrical signal as an input and providing an output signal whose instantaneous value is limited to a predetermined level; and (b) a DC voltmeter arranged to receive said clipping circuit means output signal, said DC voltmeter being operative to time average said clipping circuit means output signal and display said value of said time averaged signal, said displayed value of said time averaged signal being proportional to the area of said pattern of illumination formed on said photosensitive surface.