Optical alignment method for binocular displays

This is a continuation of application Ser. No. 441,815, filed Nov. 11, 1982.

The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.

This invention relates generally to the field of optical alignment systems and more particularly to a novel optical device for detecting misalignment in a binocular display by superimposition of the two binocular display images.

The present invention provides a simple and easy-to-use device for determining the disparity between the images transmitted along the optical axes of a binocular display system. The invention finds particular utility for the alignment, adjustment or calibration of binocular helmet mounted displays and other optical devices employing wide field of view binocular displays.

The invention comprises a pair of objective lenses for receiving the images transmitted along the two optical axes of the binocular display and focusing the images on an imaging plane for viewing. The images transmitted by the objective lenses are folded onto a single optical axis, using folding mirrors, right angle prisms, or the like, inserted along each optical axis of the binocular system, and displayed on a reticle mounted in the imaging plane as a single superimposed image. Means may be included to provide equal optical path lengths along each binocular optical axis from the lenses to the reticle. For a properly aligned binocular display system, the two images transmitted along the two binocular optical axes and superimposed using the optics of the present invention will appear as a single, well-defined image on the imaging plane. Disparity in alignment of the binocular display between the two optical axes is detected by the device of the present invention as a diffuse or double image.

It is therefore an object of the present invention to provide an improved optical alignment device.

It is a further object of the present invention to provide a device for detecting misalignment of a binocular optical display system.

It is yet another object of the present invention to provide a device for checking the alignment of helmet mounted binocular displays.

These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.

In accordance with the foregoing principles and objects of the present invention, an optical alignment device for binocular displays is provided, which comprises a pair of objective lenses and adjacent lens apertures for receiving the images transmitted along the two optical axes of the binocular display and optical folding means in the form of folding mirrors, right angle prisms, or the like, disposed along each said optical axis for optically folding said images along a single optical axis, whereby the said images may be focused as a single composite image on an imaging plane.

The present invention will be more clearly understood from the following detailed description of certain representative embodiments thereof read in conjunction with the accompanying drawing FIGURE which is a schematic plan view of a representative arrangement of optical components which the invention comprises.

Referring now to the accompanying drawing, shown therein is a schematic plan view of a novel binocular alignment/measurement device of the present invention. As shown therein, a pair of objective lens apertures 11a and 11b and objective lenses 12a and 12b are configured to be supported near the exit pupils 3a and 3b of the binocular optical display device 2 requring adjustment, alignment or calibration, and along the optical axes A and B of device 2 substantially as shown. The apertures 11a and 11b are selected to have openings of about the diameter of the pupil of the eye (about 2 mm to about 8 mm) in order to closely approximate in the alignment device the image conception of an observor O using the binocular optical display device 2 under operational conditions. Apertures 11a and 11b, lenses 12a and 12b, along with the remaining optical components hereinafter described which the invention herein includes may be supported in conventional fashion within a housing or other support structure 13.

Objective lenses 12a and 12b and apertures 11a and 11b are aligned to receive the images 4a and 4b of an object under observation as transmitted through display device 2 and represented by light rays 5a and 5b. The focal lengths of each lens 12a and 12b are selected in order to focus the images 4a and 4b on an imaging plane I, on which a calibrated reticle 14 may be mounted, at the focal plane of eyepiece 15 as seen by observer O.

Optical folding means in the form of a pair of folding mirrors or a pair of right-angle prisms 16 and 17 are provided in order to fold image 4a, as transmitted by lens 12a, along a single optical axis C and through beamsplitter 18 onto the imaging plane of reticle 14 for viewing through eyepiece 15. Image 4b, as transmitted by lens 12b is folded onto optical axis C using folding means in the form of a folding mirror or right-angle prism 19 and the reflective plane of beamsplitter 18 substantially as showing in the drawing. A glass compensating block 20 of appropriate thickness may be inserted between lens 12b and prism 19 to ensure identical optical path lengths for light rays 5a and 5b.

The images 4a and 4b are therefore combined by beamsplitter 18 to form a single image 4a, 4b on the imaging plane of reticle 14 as observed by observer O.

If optical display device 2 is in proper optical alignment, then images 4a and 4b will superimpose on each other at reticle 14 and appear to observer O as a single, well-defined image 4a, 4b. Misalignment of display device 2 may be easily detected since the image produced at reticle 14 would appear as a double or diffuse image consistent with the degree of misalignment. Alignment of display device 2 using the alignment device of this invention may then be perfected by suitably adjusting display device 2 until a distinct, single image 4a, 4b is observed on reticle 14.

The supporting structure 13 may desirably include means, shown schematically in the accompanying drawing as adjustable connector 21 interconnecting apertures 11a, b, lenses 12a, b, and prisms 16 and 19, to adjust the spacing between lenses 12a, b and apertures 11a, b to accommodate a wide range of exit pupils 3a, 3b spacings of various binocular display devices 2.

It is instructive to note that the system of the present invention could be configured so that the entire optical system can be inverted, such that an alignment determination for display device 2 first made with lenses 12a and 12b near, respectively, exit pupils 3a and 3b, may be checked by inverting the alignment device so that aperture 11a confronts exit pupil 3b and aperture 11b confronts exit pupil 3a, and then rechecking the alignment of display device 2.

The optical alignment device of the present invention may also be used to assess the divergence or convergence of a single exit pupil display designed to be observed by both eyes of an observer simultaneously, such as a head-up display. For this application, a determination of the degree of disparity is made from the image on the reticle comprising the two images of the display as transmitted through the device.

The present invention, as hereinabove described, therefore provides a novel optical device for detecting misalignment in binocular displays. It is understood that certain modifications to the invention as described may be made, as might occur to one with skill in the applicable field, within the intended scope of the appended claims. Therefore, all optical component arrangements contemplated hereunder which achieve the objects of the present invention have not been shown in complete detail. Other embodiments may be developed without departing from the spirit of this invention or from the scope of the appended claims.