Oculometer focus monitoring

Claim 2

In an oculometer comprising a source of radiant energy, light-responsive means, means directing energy from said source to fall upon the eye of an observer for reflection thereby as a diverging beam, lens means focusing energy reflected from said eye as a converging beam on said light-responsive means, and means for deriving from the output of the responsive means signals representative of the direction of regard of the observer, the improvement which comprises: an apertured member having an aperture of smaller effective diameter than the effective diameter of the lens means; means mounting said member near the lens means, with said aperture in said beam of reflected energy, for oscillation, in its own plane, transverse to the axis of the lens means; means for causing said oscillation of said member at a selected frequency, the excursion of said oscillation being no greater than the difference between the effective diameters of said aperture and said lens so that, when the eye moves out of focus with respect to the lens and the light-responsive means, a component of said selected frequency appears in said signal, while no such component is present where the eye is at the infocus portion; and synchronous demodulating means connected to derive from said component a further signal representative of the defocusing displacement of the eye.

Claim 3

Apparatus according to claim 1 in which said member is located between the observer''s eye and said lens means.

Claim 4

An oculometer comprising in combination: an image dissector tube including a photocathode, a photomultiplier, an aperture plate therebetween and a pair of orthogonal deflection coils for effectively scanning the aperture with respect to the photocathode; lens means for projecting on said photocathode the substantially circular image of a source of radiation reflected as a diverging beam from the cornea of an observer, said image being in focus for a particular position of the cornea with respect to the lens means, and moving from a particular position on said photocathode as the observer changes his direction of regard from a predetermined direction; means including an alternating voltage source of a first frequency for energizing said coils to cause said aperture to perform a circular scan of substantially the same diameter as said image, so that when the center of said scan coincides with the center of said image the output of said photomultiplier remains constant, and when said centers do not coincide said output includes an alternating voltage of the frequency of said source; synchronous switch means, energized from said source, for deriving from said output a pair of components representative of the displacement between said centers in two orthogonal directions aligned with the directions of action of said deflection coils; integrating means connecting said switch means to said coils for causing the center of said scan to follow the center of said image as the direction of regard of the observer changes; apertured means mounted in said beam of radiation near said lens means, the diameter of the aperture being substantially less than that of the lens, so that said beam is in part blocked thereby and in part passes through the aperture therein; means causing substantially rectilinear transverse oscillation of said apertured means in its own plane, in a direction aligned with one of said orthogonal directions, at a second frequency, the excursion of said vibration being no greater than the difference between said diameters, so that upon defocusing of said image by reason of axial movement of the cornea from said particular position the radiometric centroid of the image undergoes motion which has the frequency of said oscillation and which reverses in phase with reversal in the sense of said defocusing; and further synchronous switch means energized with said second frequency, for deriving from said output a component representative in sense and magnitude of said defocusing.

Claim 5

An oculometer comprising in combination: an image dissector tube including a photocathode, a photomultiplier, an aperture plate therebetween and a pair of orthogonal deflection coils for effectively scanning the aperture with respect to the photocathode; lens means for projecting on said photocathode the substantially circular image of a source of radiation reflected as a diverging beam from the cornea of an observer, said image being in focus for a particular position of the cornea with respect to the lens means, and moving from a particular position on said photocathode as the observer changes his direction of regard from a predetermined direction; means including an alternating voltage source of a first frequency for energizing said coils to cause said aperture to perform a circular scan of substantially the same diameter as said image, so that when the center of said scan coincides with the center of said image the output of said photomultiplier remains constant, and when said centers do not coincide said output includes an alternating voltage of the frequency of said source; synchronous switch means, energized from said source, for deriving from said output a pair of components representative of the displacement between said centers in two orthogonal directions aligned with the directions of action of said deflection coils; integrating means connecting said switch means to said coils for causing the center of said scan to follow the center of said image as the direction of regard of the observer changes; apertured means mounted in said beam of radiation near said lens means, the diameter of the aperture being substantially less than that of the lens, so that said beam is in part blocked thereby and in part passes through the aperture therein; means causing substantially rectilinear transverse oscillation of said apertured means in its own plane, in a direction aligned with one of said orthogonal directions, at a second frequency, the excursion of said vibration being no greater than the difference between said diameters, so that upon defocusing of said image by reason of axial movement of the cornea from said particular position the radiometric centroid of the image undergoes motion which has the frequency of said oscillation and which reverses in phase with reversal in the sense of said defocusing; and further synchronous switch means energized with said second frequency, for deriving from said output a component representative in sense and magnitude of said defocusing.