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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of telescopes which can be used both
in the day time to obtain a magnified view of a distant scene, and which
can also be used at night or under other low-light conditions to obtain a
view of the distant scene which is both magnified and intensified or
amplified to provide a visible image of a scene too dark to be viewed with
natural vision. The present invention also relates to such telescopes
which are equipped with a reticle for use in sighting a weapon in both
day-light and low-light conditions.
2. Related Technology
A conventional day/night telescopic sight is known in accord with U.S. Pat.
No. 5,084,780, issued Jan. 18, 1992 to E. A. Phillips. The Phillips patent
appears to teach a telescopic day/night sight which has several
alternative embodiments. According to one embodiment set out in the
Phillips patent, such a telescopic sight includes an objective lens behind
which is disposed an angulated dichroic mirror. This mirror divides light
coming into the sight via the objective lens into two frequency bands.
Light of longer wavelengths (lower frequencies) is allowed to pass through
the dichroic mirror to an image intensifier tube. This image intensifier
tube operates in the conventional way familiar to those ordinarily
knowledgeable about night vision devices. That is, the image intensifier
tube provides a visible image which replicates a dim image or an image
formed by invisible infrared light. Thus, the longer wavelength band which
passed through the dichroic mirror includes the infrared portion of the
spectrum, and provides to the image intensifier tube the frequencies of
light to which the tube is most responsive. The visible portion of the
light entering the sight via the objective lens is reflected by the
dichroic mirror into an optical system leading to a combiner and to an
eyepiece. At the combiner, the image provided by the image intensifier
tube is superimposed on the image from the visible-light channel of the
sight, and the resulting combined image is presented to a user of the
sight via the eyepiece.
A possible disadvantage of the Phillips sight as described above is that
the angulated dichroic mirror can introduce both parallax, astigmatism,
and color aberrations into the image provided to the user. Thus, slight
movements of the sight may cause the user to experience some shifting of
the image along a line parallel with the angulation of the mirror, while
the image does not shift along a line perpendicular to this angulation. In
other words such an angulated dichroic mirror may result it the slight
jiggling inherent in a hang-held telescope or weapon sight amplifying the
apparent movement of the image in at least one direction. This effect can
be disconcerting for the user of the device.
Other versions of the Phillips sight use a separate objective lens for both
the day channel and the night channel of the sight. These versions would
not appear to suffer from the same possible parallax problem described
above with respect to the versions using the dichroic mirror. However, the
versions of Phillips sight with two objective lenses suffer from an
increased size, weight, and expense because of the additional optics and
larger housing required to mount and protect these optics.
In each case with the sight of Phillips, the optical channels for the night
sight and the day sight are laterally offset relative to one another.
These two offset optical channels are parallel, and the image from these
channels is combined for presentation at the eyepiece. However, in each
case, the sight taught by Phillips requires separate laterally offset
optical channels, and presents the problem of correctly and precisely
superimposing the image from these two channels for the user of the sight.
SUMMARY OF THE INVENTION
In view of the deficiencies of the conventional day/night sights, it is an
object for this invention to avoid one or more of these deficiencies.
Further to the above, it is an object for this invention to provide a
day/night telescopic sight which has a day channel and a night channel
which are everywhere coaxial.
An additional object for this invention is to provide such a day/night
telescopic sight which provides for the use of a sensor other than an
image intensifier tube for the longer wavelengths of light, such as the
infrared wavelengths.
Still further to the above, such a sight according to an object of this
invention is provided with an image source such as a liquid crystal
display, which provides an image for combination with a day channel image
of the sight.
Additionally, an object for this invention is to provide such a sight
having a long wavelength sensor other than an image intensifier tube, and
a day channel with a separate objective lens so that the day channel does
not suffer color aberrations which might result from a dichroic mirror or
lens.
Accordingly, the present invention provides a telescopic day/night sight
including an objective lens through which light from a scene to be viewed
is received under both day-time and night-time (or other low-light)
conditions, a dichroic element aft of the objective lens and dividing the
received light into a visible-light frequency band and an infrared
invisible-light frequency band, a first optical path extending from the
dichroic element to an eyepiece for providing a visible-light image of the
scene to a user of the sight, a second optical path optically coaxial with
the first optical path and extending from the dichroic element to means
for receiving the invisible light and providing in response thereto a
visible image replicating the scene, a third optical path optically
coaxial with the first optical path and extending from the means for
receiving the invisible light and providing a visible image in response
thereto to provide the visible image from the means to the eyepiece
superimposed with the visible-light image and via the eyepiece to a user
of the sight.
According to another aspect, the present invention provides a telescopic
day/night sight including a single objective lens through which light from
a scene to be viewed is received, a dual-function dichroic lens/mirror
element aft of the objective lens and both dividing the received light
into a visible-light frequency band and an infrared invisible-light
frequency band, as well as refracting one of the frequency bands of light,
a first optical path extending from the dichroic element to an eyepiece
for providing a visible-light image of the scene to a user of the sight, a
second optical path extending from the dichroic element to the eyepiece
for providing a visible image replicating the scene in response to the
infrared invisible-light frequency band, the second optical path including
means for receiving the invisible light and providing in response thereto
a visible image replicating the scene.
Still additionally, the present invention provides according to another
aspect a hybrid electro-optical telescopic day/night sight comprising a
single objective lens through which light from a scene to be viewed is
received, a dual-function dichroic lens/mirror element aft of the
objective lens and both dividing the received light into a visible-light
frequency band and an infrared invisible-light frequency band, as well as
refracting one of the frequency bands of light, a first visible-light
optical path extending from the dichroic element to an eyepiece for
providing a visible-light image of the scene to a user of the sight, a
second invisible-light hybrid electro-optical path extending from the
dichroic element to the eyepiece for providing a visible image replicating
the scene in response to receipt of the infrared invisible-light frequency
band, the second optical path including electro-optical means for
receiving the invisible infrared light and providing in response thereto
an electronic image signal, image signal processing means for receiving
the electronic image signal and selectively adding indicia thereto
including an aiming reticle for the sight to provide a processed
electronic image signal, and means for providing a visible image
replicating the scene and including the added indicia in response to the
processed electronic image signal.
Additional objects and advantages of the present invention will be apparent
from a reading of the following detailed description of several
alternative preferred exemplary embodiments of the invention, taken in
conjunction with the appended drawing Figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 provides an exterior view of a telescopic day/night sight embodying
the present invention;
FIG. 2 provides a diagrammatic representation of the internal optical
structure of the sight seen in the. preceding drawing Figure;
FIG. 3 provides an exterior view of an alternative telescopic day/night
sight embodying the present invention;
FIG. 4 provides a diagrammatic representation of the internal optical
structure of the sight seen in the preceding drawing Figure;
FIG. 5 provides an exterior view of still another alternative telescopic
day/night sight embodying the present invention; and
FIG. 6 provides a diagrammatic representation of the internal optical
structure of the sight seen in the preceding drawing Figure.
DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS OF THE
INVENTION
Viewing FIG. 1, a telescopic day/night sight 10 includes a housing 12 of
stepped outer diameter, and which at a forward end includes an objective
lens 14. The term "forward" as used herein has reference to the direction
toward an object or scene to be viewed by use of the telescopic sight,
while the terms "rear" or "rearward" refer to the opposite direction
toward a user of the sight. At its rear end, the housing 12 includes an
eyepiece 16 into which the user 18 peers to obtain a magnified telescopic
view of the object or scene toward which the sight 10 is directed. The
housing 12 also provides a battery housing portion 20 having a removable
cap 22 allowing replacement of a battery (not shown) housed in the portion
20. A power switch 24 allows the user 18 to turn on and off a night vision
facility of the sight 10, as will be further described. Along the body 12
are located a pair of adjustment screw housings 26 and 28, each also
having a removable cap portion beneath which is located a respective
elevation and azimuth adjustment screw (not visible in the drawing
Figures) for an aiming reticle of the sight 10, as also will be further
explained. The sight 10 may be mounted to a weapon (not shown) so that the
sight 10 is used in directing the weapon at a target viewed through the
sight. Alternatively, sight 10 may be mounted on a tripod for surveillance
use, for example.
Viewing now FIG. 2, it is seen that the sight 10 includes objective lens
14, behind which is located an annular dual-purpose modified Magnin-type
of lens/mirror 30. The lens/mirror 30 includes a concave forward surface
upon which is carried a dichroic reflective filter coating 32. This
dichroic filter coating 32 is essentially transparent to visible light,
and is essentially reflective to invisible light in the infrared and near
infrared wavelengths. Accordingly, light from an object of scene to be
viewed by use of the sight 10, which is represented by arrows 34 on FIG.
2, is directed by objective lens 14 to the mirror lens 30. The dichroic
filter coating 32 divides this light into two frequency bands, one
including the shorter visible wavelengths and the other including the
longer invisible infrared wavelengths.
As is seen on FIG. 2, the invisible wavelengths of light, indicated with
arrow 34.sub.i reflect from the coating 32 to a secondary mirror 36, which
is centrally disposed on or adjacent to the rear surface of the objective
lens 14. So far as the invisible light 34.sub.i is concerned, the
lens/mirror 30 serves as a concentrating concave mirror. The secondary
mirror 36 is configured to correct astigmatism and flatten the visual
field of light reflected from this mirror to an image intensifier tube 38.
The image intensifier tube 38 is located within the central aperture 30'
of the lens/mirror 30. This image intensifier tube 38 includes an entrance
window 40 through which infrared light may be received. When the
intensifier tube 38 is provided with electrical power via conductors
indicated with the numeral 38', the tube provides at an image window 42 an
intensified visible image replicating the image carried by the invisible
infrared light (i.e., by the light represented with arrows 34.sub.i).
Those ordinarily skilled in the night vision art will recognize that the
image intensifier tube 38 is supplied with electrical power of appropriate
voltage and current levels by a power supply circuit (not shown) drawing
its electrical power from a battery stowed in the battery housing portion
20, and under control of the on/off switch 24. Accordingly, under
night-time or other conditions of low lighting level, the user 18 turns on
the night vision portion of the sight 10 which is provided with the image
intensifier tube 38 to obtain an intensified visible image of an invisible
night time or dimly illuminated scene. The image provided at image window
42 of the image intensifier tube 38 is transmitted via a pair of field
lenses 44 to an invertor lens 46. From the invertor lens 46, this
intensified image is projected onto a reticle/diffuser 48. As will be
explained, the user 18 can view the image on reticle/diffuser 48 via the
eyepiece lenses, indicated on FIG. 2 with the numeral 16'.
However, during day time or other conditions of adequate illumination, the
user 18 may view a visible light image through the sight 10. That is,
viewing FIG. 2, the visible light passing through lens/mirror 30 (as is
indicated with arrows 34.sub.v) passes to an annular second lens element
50. With respect to this visible light 34.sub.v, the lens/mirror 30 serves
as a concave-convex magnifying lens, which concentrates the visible light
toward the second lens element 50. This second lens element 50 projects
the visible light 34.sub.v to the same invertor lens 46 described above.
As before, the invertor lens 46 projects this light to the
reticle/diffuser 48. This reticle/diffuser 48 provides the dual functions
of providing an aiming reticle (such as a cross hairs) for use in aiming a
weapon with the sight 10, and eliminates a central obscuration or dark
spot resulting from the central secondary reflector and the annular
configuration of the elements 30, 50. That is, it is apparent that the
optical system depicted in FIG. 2 manipulates an annulus of light received
via lens 14 around the perimeter of secondary reflector 36. This annulus
of light contains a complete image of the distant scene to be viewed
through the sight 10, but provides the possibility that the user may
position the eye so that the dark spot is visible.
Preferably, the sight 10 provides an entrance pupil at objective lens 14 of
100 mm. diameter, and a magnification of 7 powers. This combination will
provide an exit pupil at eyepiece 16 of about 14 mm. Of this 14 mm. exit
pupil, a central 40 to 50 percent of the diameter may be dark. In other
words, the secondary reflector 36 has a diameter of 40 to 50 mm., and
blocks the corresponding proportionate area of the exit pupil as well. In
all locations within the exit pupil of the sight 10 and outside of this
central obscuration or dark spot, the light delivered to an eye contains
the entire image. An eye placed in this annular area will receive the full
view of the scene being observed. However, under various lighting
conditions, the human eye has a pupil diameter of from about 2.5 mm. to
about 7 mm., with an average diameter of about 5 mm. Thus, dependent upon
ambient lighting conditions, the user 18 might place the pupil of the eye
directly in the central obscuration or dark spot, and see no image.
Accordingly, the reticle/diffuser serves somewhat as a rear projection
screen to average the light over the plane of this reticle/diffuser, and
substantially eliminate the central obscuration or dark spot.
The applicant believes that either one of two alternative optical elements
will function satisfactorily for use as the reticle/diffuser element. The
first of these elements is a thin plate formed as a coherent bundle of
optical fibers. This optical fiber bundle serves to provide a relatively
thin transparent plate-like structure having a great multitude of
fine-dimension optical glass fibers which are mutually interbonded and
which extend between the opposite faces of the plate. Each of the optical
fibers outside of the central obscuration receives at its forward end
light from the scene viewed with the sight 10. At its aft end, each of the
illuminated optical fibers provides an end from which the light radiates
in a cone, effectively filling in the central obscuration with light
carrying the entire image. The reticle pattern can be etched directly on
this thin transparent optical fiber glass plate. An actual test of this
type of reticle/diffuser in test apparatus closely replicating the optical
system of the sight 10 so far as the dark spot and reticle/diffuser is
concerned provided essentially complete uniformity of image availability
across the entire exit pupil of the test apparatus.
Alternatively, the applicant has determined that a holographic diffuser
could be used to form the reticle/diffuser 48. Such holographic diffusers
provide a light diffusion angle which can be tailored across the dimension
of the diffuser so that filling in of the central obscuration is most
effective and causes the least diminution or loss of brightness of the
image in other areas of the exit pupil of the sight 10. For example, with
a holographic diffuser, light from the periphery of the image may be used
to fill in the dark spot so that the periphery of the image becomes
somewhat dimmer, but the important central area of the viewed scene
remains its greatest possible brightness. As with the optical fiber
reticle/diffuser, the holographic diffuser may be provided directly with
the desired reticle pattern. Alternatively, a separate reticle plate may
be used along with either the fiber optic diffuser or the holographic
diffuser to provide the desired reticle pattern in the sight 10.
Considering further FIGS. 1 and 2, it is seen that the visible-light image
and the visible image provided from the image intensifier tube 38 are
superimposed with one another at the reticle/diffuser 48. Accordingly, the
user 18 may use the sight in day time to see a visible light image, at
night time to see a visible image provided by the image intensifier tube
38, and under dawn or dusk conditions, for example, when both a dim
visible-light image and the visible image produced by the image
intensifier tube 38 are presented together and superimposed for viewing by
the user. Also, it will be appreciated that the sight 10 is optically
everywhere coaxial. That is, the visible light which will form the
visible-light image and the invisible light which will be directed to the
image intensifier tube 38 are everywhere coaxial. Further, the visible
image from the image intensifier tube 38 is also everywhere coaxial with
the visible light path of the sight so that a compact arrangement of the
elements for the sight is obtained.
FIGS. 3 and 4 provide exterior and diagrammatic views similar to FIGS. 1
and 2, but showing a more detailed alternative embodiment of the present
telescopic day/night sight. In order to obtain reference numerals for use
in describing the structure seen in FIGS. 3 and 4, features which are
analogous in structure or function to those introduced above are
referenced with the same numerals used above and increased by 100. Viewing
now FIGS. 3 and 4 in conjunction with one another, it is seen that the
sight telescopic day/night sight 110 of FIG. 3 similarly includes a
housing 112 of stepped outer diameter. The housing 112, is "cranked", or
off set between its forward and aft end so that the eyepiece 116 is not
coaxial with the objective lens 114. The housing 112 includes a battery
housing portion 120 having a removable cap 122, and a power switch 124
allowing the user 118 to turn on and off the night vision facility of the
sight 110. Housing 112 also includes a pair of adjustment screw housings
126 and 128, for respective elevation and azimuth adjustment screws.
Viewing now FIG. 4, it is seen that the lens mirror element 130 includes a
pair of annular optical lens elements 52 and 54. The first of these lens
elements (element 52) is a concave-convex lens having its forward concave
surface disposed toward the objective lens 114. The second lens element 54
is similar to a Mangin reflector element, and carries the reflective
filter coating 132 on its forward concave surface. Because of the
positioning of the first lens element 52 in front of the reflective filter
coating 132, light in the longer wavelength frequency band (i.e., the
invisible infrared light) benefits from two refractive passages through
the element 52. That is, the longer infrared light admitted via objective
lens 114 passes first rearwardly through the lens element 52 to the filter
coating 132 on the forward surface of lens element 54 where it is
reflected. This reflected infrared light passes again through the lens
element 52 on its way to the secondary reflector 136.
In this embodiment of the invention, in part because of the dual refractive
effect obtained from the first lens element 52, the secondary reflector
136 is much less concave than was required by the first embodiment of the
invention set forth in FIGS. 1 and 2. The secondary reflector 136 is
nearly flat, with some aplanarity for purposes of correcting astigmatism
and flattening the visual field of the image provided to the image
intensifier tube 138. An additional simple meniscus lens element 56 at the
entrance window 140 of the intensifier tube 138 serves to further correct
residual astigmatism and flatten the image field. A concave-convex lens
element 58 disposed behind the image window 142 of the image tube 138
serves to project the intensified image from this tube to a set of
invertor lenses, generally referenced with the numeral 146. In this case,
the invertor lenses 146 are a triplet set of lenses similar to a Cooke
triplet invertor. The lenses 146 project the intensified image from image
tube 138 to a reticle/diffuser 148.
As was the case also with the lens/mirror 30 of the first embodiment of the
invention described above, the lens/mirror 130 includes a refractive lens
element. The second lens element 54, which at its forward surface carries
the reflective filter coating 132, serves to also refract the visible
light frequency band passing through the coating 132 and also through this
lens element 54. Behind the lens element 54, the second lens element 150
is composed of a pair of lenses 60 and 62. An additional set of annular
field lenses 64 and 66 are located rearwardly of the lenses 60 and 62 in
order to project the visible light image onto the reticle/diffuser 148. It
will be recognized that the objective lens system described for this
embodiment is similar to a Petzval objective design, with the added
feature that the lenses are all annular. The annular lenses of the present
telescopic sight are seen to accommodate the image intensifier tube 38 (or
138) in a desirable location for purposes of receiving and amplifying
light in the invisible infrared frequency band. At the reticle/diffuser
148, either the visible light image, the intensified image from the image
intensifier tube 138, or both superimposed together, is visible to the
user via eyepiece 116'.
However, the embodiment of FIGS. 3 and 4 is seen to also include a pair of
folding mirrors or prisms 68 and 70 for the purpose of moving the eyepiece
116 off axis with respect to the large objective lens 114. An advantage of
having the eyepiece 116 offset with respect to the objective lens is
recognized to reside in the possibility of placing the eyepiece 116 closer
to the sighting line established by the conventional "iron sights" of a
weapon such as a rifle. Thus, the user of the rifle upon which the sight
110 is mounted with be able to use the sight 10 with a hold on the weapon
the same as or similar to that to which the user is accustomed. It will be
noted that the image provided by the visible light portions of the sight
10 form an inverted image at reticle/diffuser 148. Thus, an invertor Cooke
triplet lens set 72 is provided to re-invert the image and provide an
erect image to the user 118 via the eyepiece lenses 116'. Also, it should
be noted that the offset of the optical pathway of the sight 130 (i.e.,
the "cranking"of the housing 112), does not alter the coaxial nature of
the sight. That is, the optical pathways remain everywhere coaxial. The
offset of the optical pathway at reflectors 66, 68 to allow eyepiece 116
to be offset relative to the objective lens 114 is after the
reticle/diffuser where the visible-light image and the visible image
produced from the invisible infrared light are superimposed on one another
and are coaxial. Accordingly the advantages of a compact arrangement for
the sight 110 is preserved.
FIGS. 5 and 6 present yet another alternative embodiment of the invention,
in which the image in the invisible frequency band (i.e., in the infrared
wavelengths) is converted by a sensor into an electrical signal (either
with or without frequency shifting and amplification as are provided by an
image intensifier tube), is electronically manipulated to provide a
reticle as well as other desired indicia on the image, and is then
reconverted back to a visible image by a display device such as a liquid
crystal display (LCD) screen. In order to obtain reference numerals for
use in describing the structure seen in FIGS. 5 and 6, features which are
analogous in structure or function to those introduced above are
referenced with the same numerals first used above and increased by 200.
Viewing more particularly FIGS. 5 and 6 in conjunction with one another,
it is seen that the sight telescopic day/night sight 210 of FIG. 5
includes a housing 212 of stepped outer diameter. The housing 212 carries
a forward objective lens 214, and includes a battery housing portion 220
having a removable cap 222. A power switch 224 allows the user 218 to turn
on and off the night vision facility of the sight 210. Housing 212 also
includes a pair of adjustment screw housings 226 and 228 with removable
cap portions for protecting respective elevation and azimuth adjustment
screws.
FIG. 6 shows that the sight 210 includes a lens/mirror element 230
including a pair of annular optical lens elements 252 and 254. The first
of these lens elements (element 252) is a concave-convex lens having its
forward concave surface disposed toward the objective lens 214. The second
lens element 254 is similar to the lens element 54 introduced above, and
is similarly a dual-function optical element in the sight 210. The lens
element 254 carries the reflective filter coating 232 on its forward
concave surface. Because of the positioning of the first lens element 252
in front of the reflective filter coating 232, light in the invisible
infrared wavelength frequency band makes two refractive passages through
the element 252. The secondary reflector 236 is again nearly flat, with
some aplanarity for purposes of correcting astigmatism and flattening the
visual field of the image provided to an image detector 74. The image
detector 74 may include an image intensifier tube 238. However, disposed
at the image window of the intensifier tube 238 is a charge coupled device
(CCD) 76. This CCD is similar to the image detector in a video camera so
that the visible image provided by the image intensifier tube 238 is
converted to an electrical signal by the CCD 76. An electrical cable 78
connects to the CCD 76, and carries the electrical image signal from this
CCD to an image signal processing circuit, schematically depicted and
indicated with the numeral 80. Alternatively, the image detector 74 may
include a cooled or uncooled infrared detector for converting the infrared
light energy delivered by the optical elements depicted and described
directly to an electrical signal. In this case also, the cable 78 would be
used to carry the electrical image signal to the processing circuit 80.
As was the case also with the lens/mirror 30 and 130 of the embodiments
described above, the lens/mirror 230 performs a dual function by including
a refractive lens element. The second lens element 254, which at its
forward surface carries the reflective filter coating 232, serves to also
refract the visible light frequency band passing through the coating 232
and also through this lens element 254. Again, behind the lens element
254, the second lens element 250 is composed of a pair of lenses 260 and
262. An additional set of annular field lenses 264 and 266 are located
rearwardly of the lenses 260 and 262 in order to project the visible light
image onto the reticle/diffuser 248. However, it will be noted that in
this embodiment of the invention, the | | |
