GB2063501A - Night Vision Apparatus - Google Patents

Abstract

The invention relates to night vision apparatus and particularly to apparatus which employs image intensifiers and which are used by aircraft pilots for piloting, for surveillance or target acquisition. The night vision apparatus includes an optical channel having an eyepiece (2) and an objective lens (10), an annular, red filter (5) associated with the objective lens, a correction lens (4) for viewing near scenes mounted in the centre of the annulus of the filter, and preferably an image intensifier (3) mounted between the eyepiece (2) and the filter (5). <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Night Vision Apparatus The invention relates to night vision apparatus and particularly, though not exclusively, relates to apparatus which employ image intensifiers and which are for use by pilots for piloting, for surveillance or target acquisition.

A typical image intensifying system for use by helicopter pilots, includes an image intensifier tube mounted in lightweight, head-mounted binoculars. One disadvantage of the binoculars is that they require refocussing when, for example, a change from instrument scanning to surveillance of a distance scene is made.

One solution which has been proposed to overcome problems raised by refocussing whilst performing flying or other tasks is to use modified binoculars of which the monocular parts each have an objective lens filter.

The objective lens filters of the modified binoculars each comprise a plane, red filter having a small, approximately 1.5 mm diameter, hole at its centre. The small hole gives a large depth of field and enables near scenes such as instrument panels to be viewed by the pilot. A disadvantage associated with this solution is that a high level of blue illumination is required for the instrument panels or other near scene items. A further disadvantage is that diffraction through the hole limits the resolution level which is obtainable.

The present invention provides night vision apparatus which may be satisfactorily used with a lower level of near scene illumination, and which enables both far scene images, and near scene images to be in-focus.

According to the present invention night vision apparatus includes an optical channel having an eyepiece and an objective lens, an annular, red filter associated with the objective lens, a correction lens for viewing near scenes mounted in the centre of the annuius of the filter, and an image intensifier mounted between the eyepiece and the filter.

Preferably the red filter cut is 550 nm.

The near scene correction lens may have a focal length of between 300 mm and 900 mm. In a preferred embodiment of the invention the focal length of the lens is 600 mm.

The correction lens may be associated with a blue and/or green filter or may be composed of blue and/or green filter material.

The optical channel may have a stop at its objective aperture which may comprise an annular stop which reduces the aperture by 80% for viewing moonlit scenes.

An embodiment of the invention will now be described by way of example only and with reference to the drawing which shows an optical arm of a binocular night vision apparatus.

A scene (not shown) is viewed by an eye 1 of an observer along an optical path 8 via an eyepiece lens 2, an image intensifier 3, and an objective lens 10 and lens and filter pair 9 mounted in a tube 7 which forms the optical arm of the binocular apparatus. The lens and filter pair 9 includes an annular red filter 5 and a convex correction lens 4 coaxially mounted in the annulus of the filter 5. The red filter 5 is composed of filter glass having 50% transmission at 585 nm and 95% transmission beyond 620 nm, and having a diameter of 30 mm. The lens 4 has a focal length of 600 mm and a diameter of 6 mm. The tube 3 carries a removable annular stop having an aperture area which is 20% of the lens and filter pair 9 area.

In use, in an aircraft cockpit which is illuminated by a lamp having a filter which passes light up to 550 nm, a scene ahead of the aircraft is viewed using the above described binocular night vision apparatus. Aircraft instruments will be viewed only through the lens 4 which is at a less extreme focal ratio than full aperture and gives high resolution and a large depth of field.

Light from the cockpit, which will be predominantly green and blue, will not be passed by the red filter 5 which only passes light from the exterior scene. The stop 6 is employed in moonlit conditions to retain a suitable contrast between cockpit images and the image of the scene. If the stop 6 is dispensed with it will be necessary to increase the cockpit illumination until a satisfactory contrast is achieved.

In a modification of the above embodiment the convex lens is composed of filter glass, or is associated with an adjacent filter, the filter passing light up to 550 nm.

Claims

1. Night vision apparatus including an optical channel having an eyepiece and an objective lens, an annular, red filter associated with the objective lens, a correction lens for viewing near scenes mounted in the centre of the annulus of the filter, and an image intensifier mounted between the eyepiece and the filter.

2. Night vision apparatus as claimed in claim 1 wherein the red filter has a cut off point of 550 nm.

3. Night vision apparatus as claimed in claim 1 or claim 2 wherein the correction lens has a focal length of between 300 mm and 900 mm.

4. Night vision apparatus as claimed in any of the above claims further including a blue and/or green filter associated with the correction lens.

5. Night vision apparatus as claimed in any of claims 1 to 4 wherein the correction lens is composed of blue and/or green filter material.

6. Night vision apparatus as claimed in any of the above claims further including an annular stop in the optical channel for viewing night scenes.

7. Night vision apparatus as claimed iri claim 6 wherein the stop reduces the exit aperture by 80%.

8. Night vision apparatus substantially as described herein with reference to the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or Relating to Night Vision Apparatus The invention relates to night vision apparatus and particularly, though not exclusively, relates to apparatus which employ image intensifiers and which are for use by pilots for piloting, for surveillance or target acquisition. A typical image intensifying system for use by helicopter pilots, includes an image intensifier tube mounted in lightweight, head-mounted binoculars. One disadvantage of the binoculars is that they require refocussing when, for example, a change from instrument scanning to surveillance of a distance scene is made. One solution which has been proposed to overcome problems raised by refocussing whilst performing flying or other tasks is to use modified binoculars of which the monocular parts each have an objective lens filter. The objective lens filters of the modified binoculars each comprise a plane, red filter having a small, approximately 1.5 mm diameter, hole at its centre. The small hole gives a large depth of field and enables near scenes such as instrument panels to be viewed by the pilot. A disadvantage associated with this solution is that a high level of blue illumination is required for the instrument panels or other near scene items. A further disadvantage is that diffraction through the hole limits the resolution level which is obtainable. The present invention provides night vision apparatus which may be satisfactorily used with a lower level of near scene illumination, and which enables both far scene images, and near scene images to be in-focus. According to the present invention night vision apparatus includes an optical channel having an eyepiece and an objective lens, an annular, red filter associated with the objective lens, a correction lens for viewing near scenes mounted in the centre of the annuius of the filter, and an image intensifier mounted between the eyepiece and the filter. Preferably the red filter cut is 550 nm. The near scene correction lens may have a focal length of between 300 mm and 900 mm. In a preferred embodiment of the invention the focal length of the lens is 600 mm. The correction lens may be associated with a blue and/or green filter or may be composed of blue and/or green filter material. The optical channel may have a stop at its objective aperture which may comprise an annular stop which reduces the aperture by 80% for viewing moonlit scenes. An embodiment of the invention will now be described by way of example only and with reference to the drawing which shows an optical arm of a binocular night vision apparatus. A scene (not shown) is viewed by an eye 1 of an observer along an optical path 8 via an eyepiece lens 2, an image intensifier 3, and an objective lens 10 and lens and filter pair 9 mounted in a tube 7 which forms the optical arm of the binocular apparatus. The lens and filter pair 9 includes an annular red filter 5 and a convex correction lens 4 coaxially mounted in the annulus of the filter 5. The red filter 5 is composed of filter glass having 50% transmission at 585 nm and 95% transmission beyond 620 nm, and having a diameter of 30 mm. The lens 4 has a focal length of 600 mm and a diameter of 6 mm. The tube 3 carries a removable annular stop having an aperture area which is 20% of the lens and filter pair 9 area. In use, in an aircraft cockpit which is illuminated by a lamp having a filter which passes light up to 550 nm, a scene ahead of the aircraft is viewed using the above described binocular night vision apparatus. Aircraft instruments will be viewed only through the lens 4 which is at a less extreme focal ratio than full aperture and gives high resolution and a large depth of field. Light from the cockpit, which will be predominantly green and blue, will not be passed by the red filter 5 which only passes light from the exterior scene. The stop 6 is employed in moonlit conditions to retain a suitable contrast between cockpit images and the image of the scene. If the stop 6 is dispensed with it will be necessary to increase the cockpit illumination until a satisfactory contrast is achieved. In a modification of the above embodiment the convex lens is composed of filter glass, or is associated with an adjacent filter, the filter passing light up to 550 nm. Claims

1. Night vision apparatus including an optical channel having an eyepiece and an objective lens, an annular, red filter associated with the objective lens, a correction lens for viewing near scenes mounted in the centre of the annulus of the filter, and an image intensifier mounted between the eyepiece and the filter.

2. Night vision apparatus as claimed in claim 1 wherein the red filter has a cut off point of 550 nm.

3. Night vision apparatus as claimed in claim 1 or claim 2 wherein the correction lens has a focal length of between 300 mm and 900 mm.

4. Night vision apparatus as claimed in any of the above claims further including a blue and/or green filter associated with the correction lens.

5. Night vision apparatus as claimed in any of claims 1 to 4 wherein the correction lens is composed of blue and/or green filter material.

6. Night vision apparatus as claimed in any of the above claims further including an annular stop in the optical channel for viewing night scenes.

7. Night vision apparatus as claimed iri claim 6 wherein the stop reduces the exit aperture by 80%.

8. Night vision apparatus substantially as described herein with reference to the drawings.