GB2099171A - Variable-direction field optical radiation directing apparatus - Google Patents

Abstract

An optical system for receiving radiation from within a variable direction field and passing it to a detector (1) or for projecting a variable direction radiation beam comprises lens mounting means a convergent lens (8) and a divergent lens (10) rotatable together about a point (14) on the axis of an intermediate fixed divergent lens (9). <IMAGE>

Description

SPECIFICATION Optical radiation directing apparatus This invention relates to radiation directing apparatus wherein an optical system transfers opti cai radiation between a fixed position, at which there may reside a radiation-sensitive detector element or a radiation source, and a spatial field, i.e. a field-ofview from which radiation is to be received or a field into which a radiation beam is to be directed, the direction ofthe field being controllabiy variable.

Optical systems for varying the axial direction of the field-of-view of a radiation detector without actually moving the detector are known but tend to be somewhat complex, i.e. to include a relatively large number of optical elements with consequent increased power loss and aberrations.

According to the invention, there is provided optical radiation directing apparatus comprising an optical system wherein relatively movable optical elements are operable for transferring optical radiation between a position at one of an input side and an output side of the system and a variable-direction field at the other of said input side and said output side, characterised in that said optical system comprises lens mounting means, a convergent lens, and first and second divergent lenses, the lenses being supported by said mounting means with the first divergent lens between the convergent lens and the second divergent lens and fixed in relation to said position, the second divergent lens between the first divergent lens and said position, and the second divergent lens and the convergent lens being fixed relative to one another but being together able to turn about a pivot point between the first and second divergent lenses to vary the direction of said field.

Said mounting means may comprise gymbal mounting means supporting said convergent lens and the second divergent lens for turning movement about said pivot point with two degrees of freedom.

Advantageously each divergent lens comprises at least one concave-convex lens element, the or each element of each lens being positioned with its concave surface facing generaily towards the other lens and the said pivot point is the point of intersection between the optical axes of the lenses.

Preferably, said optical system includes a further convergent lens between said second divergent lens and said position and in fixed relationship to said position.

Advantageously, either divergent lens is operable for receiving a beam of radiation converging towards a point at least near the other divergent lens and for causing that beam to become substantially parallel.

The apparatus may include a radiation sensitive detector element at said position, the apparatus then being operable for imaging radiation received from within a variable-direction field-of-view onto said detector element, or it may have an optical radiation source at said position in which case the apparatus becomes operable for projecting a beam of radiation into said field.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings in which: figure 1. is a sectional view of infra-red radiation detector apparatus, and figure 2 is a diagrammatic view of a modification of the figure 1 apparatus.

The apparatus shown in figure 1 comprises an infra-red radiation detecting device 1 and an optical system which is operable for directing onto the sensitive surface ofthe device 1 radiation received from within a field-of-view 2 symmetrical about an axis 3, the direction of the field-of-view 2 being variable within a conical overall field-of-view4which is symmetrical about an optical axis 5. The device 1 is fixed with its sensitive surface aligned with an image plane 6 which is perpendicularto axis 5 and intersects that axis at a point 7, the centre of the sensitive surface of device 1 being positioned at this intersection point.

The optical system consists of a series of lenses namely, in the order in which they appear two radiation entering the apparatus, a convergent objective lens 8, a first and then a second divergent lens 9 and 10 respectively, and a convergent focussing lens 11.

The lenses 9 and 11 are fixed in position with the optical axes thereof aligned along axis 5. Meanwhile, lenses 8 and 10 are fixed relative to one another with their optical axes aligned along axis 4 but are supported by a gymbal mounting arrangement comprising frame members 12 and pivot couplings 13 whereby these lenses can be moved so that axis 4 turns about a point 14 lying on axis 6 between the lenses 9 and 10 with two degrees of freedom, i.e.

within the plane ofthe drawing figure and in a plane perpendicularthereto. Each of the lenses 9 and 10 is a doublet lensi.e. comprising two closely spaced elements. Each element has one convex and one concave surface, the elements of lens 9 having their convex surfaces nearer the objective lens 8 and the elements of lens 10 having their convex surfaces nearer the focussing lens 11. Although it is not essential, in the illustrated case, the lenses 9 and 10 are substantially identical, apart from facing in opposite direction. The concave and convex surfaces of all the lens elements are part-spherical with respective centres on the axis 6.

A beam of infra-red radiation 15 received by lens 8 from a distant point source (not shown) and symmetrical about the optical axis 3 is converged by the lens 8 towards the point 16 where the axis 3 intersects the concave surface of the inner element of lens 10. The lens 9 is such that the central ray 17 of beam 15, i.e. the part of the beam which is travelling along the optical axis 3 directly towards point 16, is so deflected that its angle of incidence e on the axes 5 is one half of what it would have been if the lens 9 were not present, i.e. if the ray had carried on along the axis 3 to the point where this axis crosses axis 5.

As a result, ray 17 becomes incident upon the con cave inner element surface of lens 10 at the position of coincidence of this surface with axis 5. Consideration of the system geometry will show that, at this position of incidenece, the deflection applied by lens 10 corresponds to that applied by lens 9 at the point where the central ray 17 passed therethrough.

Hence, lens 10 deflects ray 17 so that it emerges from lens 10 along the axis 5. Meanwhile, the remainderofthe radiation within beam 15 is so deflected by lens 9 that it passes between the lens 9 and lens 10 in directions parallel to ray 17, i.e. the original parallel beam received and converged by lens 8 is in effect re-collimated by lens 9, and this recollimated beam is diverged by lens 10 so that it emerges symmetrically about the ray 17 and axis 5 as if diverging from the point 18 where axis 5 intersects the concave surface of the inner element of lens 9. This divergent beam is focussed by lens 11 on to the detector element 1. Further consideration of the figure will show that the above occurs when the angle between the axes 3 and 5 is other than that shown, including when they are in alignment.

Also, ifthe original radiation is received from a received scene, an image thereof is formed at the image plane 7 and, provided the lens parameters are correctly chosen, this image will not suffer significant rotation as the angle between axes 3 and 5 is varied.

The limits of possible variation of the angle between axes 3 and 5, and hence the size of the overall field-of-view 4 within which the instant field-of-view 2 (defined by the size of detector device 1) may be moved are determined by the particular construction of the illustrated apparatus. Clearly, however, not all the features of this particular construction are essential. For example, it is not essential that the lenses 9 and 10 be identical whether in size, shape or optical power. As a consequence of this, of course, it is also not essential that the beam 15 should be parallel as it passes between lens 9 and 10.For example, the lens 8 and/or the lens 9 may be such that the beam is divergent or convergent as it reaches lens 10 and the lens 10 and/or the lens 11 may be appropriateiy designed to achieve the desired focussing onto detector 1 (assuming, of course, that such focussing is desired - it may not be. For example, possibly the original parallel beam is required to emerge from lens 11 and, of course, the power of lens 11 could be chosen to provide this).

One possibly advantageous modification of what is shown would be to make one of the lenses 9 and 10 of such dimensions that the two can overlap or become partly nested one within another at the limits of the rotation of lenses 8 and 10 about point 14. This may remove a structural limitation on the maximum angle between axes 3 and 5, i.e. it may increase the size of the overall field-of-view 4. Any or all the lenses could be spherical or aspherical lenses and either of the lenses 8 and 11 could be a multielement lens, for example a doubiet. Meanwhile, the lenses 9 and 10 are not necessarily doublets as shown but could instead each comprise more than two elements or only one.For example, in the modification shown in figure 2 there are again objective and focussing lenses 20 and 21 respectively and a radiation detector 24 arranged as in the figure 1 embodiment but the lenses 9 and 10 of that embodiment are replaced by respective single concavoconvex element lenses 22 and 23. These two lenses are arranged with the concave surfaces thereof facing each other. The two lenses are again identical and have part-spherical convex surfaces, the lenses being spaced so that the centres of curvature of these convex surfaces both lie at the point 25 about which the movable optical axis 26 turns. Meanwhile, the concave surfaces of the lenses may also be partspherical, the centres of curvature thereof lying at respective points 27 and 28 on the fixed central axis 29.The power of the lens 22 is such that a ray of radiation 30 arriving along the axis 26 is diverted so as to become incident on the concave surface of the lens 23 at the point at which this surface is intersected by the axis 29 whereby, lens 23 being identical to lens 22, the ray becomes deflected along axis 29.

Instead of apparatus for receiving radiation, the optical systems described could form part of apparatus for projecting radiation to a controllable portion of an overall conical volume of space. For this, of course, the detector device 1 or 24 can be simply can be simply replaced by a suitable radiation source.

Whether the apparatus is for receiving or projecting radiation, this can be any kind of optical radiation including say the visible band as well as the infrared radiation already mentioned.

As mentioned earlier, the particularly illustrated form of the lenses 8 to 11 or 20 to 23 is not essential.

It is possible also that the focussing lens 11 or 21 is not needed at all. For example, where the optical system is for use in association with some separate optical apparatus, it may be that the function of the focussing lens 11 or 22 can be performed by a suitable lens arrangement already provided in that separate apparatus.

Claims (7)

1. Optical radiation directing apparatus comprising an optical system wherein relatively movable optical elements are operable for transferring optical radiation between a position at one of an input side and an output side of the system and a variabledirection field at the other of said input side and said output side, characterised in that said optical system comprises lens mounting means, a convergent lens, and first and second divergent lenses, the lenses being supported by said mounting means with the first divergent lens between the convergent lens and the second divergent lens and fixed in relation to said position, the second divergent lens between the first divergent lens and said position, and the second divergent lens and the convergent lens being fixed relative to one another but being together able to turn about a pivot point between the first and second divergent lenses to vary the direction of said field.

2. Apparatus according to claim 1, wherein said mounting means comprises gymbal mounting means supporting said convergent lens and said second divergentlensforturning movement about said pivot point with two degrees of freedom.

3. Apparatus according to claim 1, wherein each divergent lens comprises at least one concavoconvex lens element, the or each element of each lens being positioned with its concave surface facing generally towards the other lens and wherein the said pivot point is the point of intersection between the optical axes of the lenses.

4. Apparatus according to claim 1, wherein said optical system includes a further convergent lens between said second divergent lens and said position and in fixed relationship to said position.

5. Apparatus according to claim 1, wherein either divergent lens is operable for receiving a beam of radiation converging towards a point at least near the other divergent lens and for causing that beam to become substantially parallel.

6. Apparatus according to claim 1, including a radiation sensitive detector element at said position, the apparatus being operable for imaging radiation received from within field-of-view onto said detector element.

7. Optical radiation directing apparatus substantially as hereinbefore described with reference to the accompanying drawings.