Pilkington Pe Limited

Philip J Rogers

Michael Roberts

Duncan R Campbell

A two-stage multi-spectral imaging system comprising a reflective objective and a reflective relay aligned on a common optical axis, the objective being arranged to form an intermediate image and the relay being arranged to deliver image-forming radiation emanating from the intermediate image to a focal plane, wherein the objective is formed by a large concave primary mirror which is apertured on-axis and a small secondary mirror generally disposed in the form of a &ldquo;Cassegrain&rdquo; objective, the relay is formed by a pair of confronting mirrors each being apertured on-axis to enable passage of radiation into and out of the relay, and the relay being positioned to provide space between the relay and the focal plane to accommodate waveband selective splitting optics if so desired.

Optical imaging system

A switchable dual field of view objective system 20 comprises a front lens A and a rear lens C with an intermediate lens B switchable between in-use and out-of-use positions. Lens A is positively powered and lens C is negatively or positively powered but has little power in comparison to lens A. Lens C has two lens components 24, 25 of which component 24 is negatively powered and is located proximal to intermediate lens B. Lens B and component 24 are carried in common by a carrier 28 which is movable along the axis to provide distance focussing in both fields of view.

Optical systems

A two-stage optical imaging system which is capable of operating in the infra red and which is compact, the system comprising an objective generally in the form of a Cassegrain system with primary and secondary mirrors A, B together with a relay C which may be reflective, refractive or refractive and diffractive, the relay C being located co-axially between the primary and secondary mirrors A, B.

Head-up displays

This invention is concerned with display apparatus of the Head-Up-Display (H.U.D.) type which finds utility in e.g. fighter aircraft. The invention is concerned with providing an H.U.D. which has a profile depth which is substantially and preferably much less than the diameter of the exit lens. The arrangements of the H.U.D. include a cathode ray tube (C.R.T.) display source, a collimating optical means having a plurality of lenses with at least an entrance lens and an exit lens together with a prism and combining means for combining displayed visual information with the view of the scene or object. The prism is so arranged in relationship to the display source that internal reflection of light from the display source within the prism and transmission of light towards the combining means is such as to enable the modular unit profile depth to be between 40% and 60% less than the exit lens diameter. Embodiments are shown which incorporate compensating means to compensate for CRT mechanical axis tilt at an angle with respect to e.g. the aircraft horizontal.

Optical apparatus for superimposing displayed visual information

Optical viewing apparatus has an obective lens for focussing radiation from a scene or object to form an image on a detector and means for producing a visible display of the image which is viewed through an eye-piece lens. The objective lens is designed to impose a substantial level of barrel distortion on the image and the eye-piece lens imposes a substantial level of pincushion distortion on the observer's view to give improved central resolution. The radiation focussed by the objective lens may be visible or invisible, e.g. infra-red.

Optical apparatus

An 'eye-piece' system for an infra-red afocal telescope comprises a back element of positive power having a convex front surface and a curved back surface, and a pair of elements closely spaced to define a gas lens therebetween, the front element of the pair having a concave front surface whose radius of curvature is equal to or greater than that of the convex back surface of the back element of the pair, the pair of elements in combination with the gas lens therebetween being of positive power. The 'eye-piece' system can be used in combination with an objective lens system, which may be catadioptric or all refractive, to provide a collimated magnified view of a scene or object, from which infra-red radiation is received, at a real exit pupil where a scanner operates.

Infra-red optical systems

Optical apparatus for biocular viewing of relatively low cost and light weight comprises a solid Cassegrain configuration in a solid meniscus element having a negative lens element cemented to its convex face and an associated corrector lens element which provide a magnified collimated image of an object for viewing by a pair of telescopes having light folding means to provide an exit pupil separation suitable for two eye viewing. At least some of the lens elements may be of plastics material and aspheric surfaces may be employed. The apparatus is particularly useful for night vision goggles having a single image intensifier tube.

An 'eye-piece' system for an infra-red afocal telescope comprises a positive back element having a concave or convex back surface and a convex front surface, and a pair of elements closely spaced to define a gas lens therebetween, the back element of the pair having a convex back surface and the front element of the pair having a concave front surface, the pair of elements in combination with the gas lens therebetween being of positive power. The 'eye-piece' system can be used in combination with an objective lens system to provide a collimated magnified view of a scene or object, from which infra-red radiation is received, at a real exit pupil where a scanner operates, and can provide a wide field of view of around 70 degrees or more in the scanner space.

A transfer lens comprises a first field-flattening component of negative power, a second component of positive power providing overcorrect astigmatism, a third component of positive power consisting of a plurality of positive members providing most of the power of the overall lens and whose undercorrect astigmatism is corrected by the overcorrect astigmatism of the second component, and a fourth component of negative power which increases the field angle. The lens is particularly useful in a head-down display having two primary displays from which light travels to a combiner so that the transfer lens produces a combined image. A Fresnel field lens is preferably located at the image position.

Transfer lens and head-down display using the same

The invention provides an objective lens with a front lens group and a rear lens group spaced apart from the front group. The front group comprises at least two doublet components one of which is a crown positive element cemented to a flint negative element which has a higher refractive index and dispersion values than those of the crown glass. The other doublet component of the front group is a crown positive element and a flint negative element in which the flint and crown glasses have similar refractive indices but dissimilar dispersions with the flint glass having a positive red relative partial dispersion deviant.

Objective lenses

The 'eye-piece' for a non-Gallilean afocal infra-red telescope comprises a front element which is meniscus with a convex back surface of greater radius of curvature than its concave front surface but which has a thickness such that it is of positive power, and a back element of positive power with a convex front surface and a convex or concave back surface. Such an 'eye-piece' can be used in combination with a variety of objective lens systems.

A biocular magnifying lens suitable for use as an eyepiece in a night vision device comprises from front to back a positive element which is bi-convex or meniscus convex towards the front, a negative meniscus element concave towards the front, a positive singlet or doublet element which is convex towards the front, a positive element which is bi-convex or meniscus convex towards the front, and a positive meniscus element convex towards the front.

Lenses

The invention provides a telephoto lens with a positive front group of lens elements, a negative middle group of lens elements and a rear positive part comprising a lens element or group of lens elements. The front group of elements includes at least one positive doublet consisting of a positive element of a crown glass type in front of a negative element of a flint glass type having a positive red relative partial dispersion coefficient deviation. The middle group of elements includes a positive lens element of a crown glass type and a negative lens element of a flint glass type having a positive red relative partial dispersion coefficient deviation. The rear element or group of elements may consist of a doublet component comprising a negative bi-concave element and a positive bi-convex element, the rear part of the telephoto lens being well separated from the negative middle part.

An objective lens particularly for use in a low light level or night vision system designed to introduce a controlled amount of barrel distortion at the edges of its field of view to permit use with a flat input faced imaging tube.

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Clwyd, United Kingdom

Philip J Rogers