Note: Descriptions are shown in the official language in which they were submitted.
~ W092/037~ 2 ~ ~ 5 6 ~/2 PCT/NL9l/00~4g
Title: Combined daY viewinq and niqht viewinq telesco~e
The invention relates to a combined day viewing and
night viewing telescope, comprising a housing with an
entrance aperture and an exit aperture, first light guide
means for guiding light received through the entrance
aperture and intended for night viewing to an input of an
image converter; and second light guide means for guiding
light produced by the image converter at an output
thereof to the exit aperture.
Such a combined day viewing and night viewing
telescope, hereinafter described by the term "day/night
viewing telescope", is known from US Patent Specification
4,629,295.
: A disadvantage of this known day/night viewing
telescope is that a separate second entrance aperture is
. 15 required for receiving light for day viewir~. This known
- day/night viewing telescope is thus essentially composed
of two telescope parts situated adjacent to or above one
another, and the light produced by the image converter at
.~ the exit of the part designed for night viewing has to be
20 coupled by means of the second guide means into the
` telescope part designed for day viewing. The above-
mentioned US Patent Specification 4,629,295 describes,
;
for example, a partially transmissive mirror 12 for that
purpose.
The object of the invention is to improve the known
; day/night viewing telescope. In particular, the object of
the invention is to provide a day/night viewing telescope
of reduced dimensions and a reduced weight. More par-
ticularly, the object of the invention is to provide a
30 day/night viewing telescope with a combined entrance a-
~; perture for day viewing and night viewing.
i~ To this end, according to the invention the
` day/night viewing telescope of the above-mentioned type
.' is designed to receive light intended for day viewing
35 also through the entrance aperture intended for night
viewing, and the telescope is provided with light
separating means for separating said light for day
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W O 92/037~4 2 0 g ~ 6 0 2 PC~r/NL91/00149
;~ viewing received through the entrance aperture from the
`~ light intended fori night viewing and directing said day
viewing to the exit aperture via an optical path running
outside the image converter.
In a first embodiment, the light separating means
are designed for spatially separating the light intended
for day viewing and the light intended for night viewing,
and thereto comprise a first optical system with
positive strength positioned in the optical path between
the entrance aperture and the input of the image
converter, the surface area of which system is smaller
than the surface area of the entrance aperture.
In a second embodiment, the light separating means
are designed for separating in time the light intended
for day viewing and the light intended for night viewing,
and thereto comprise a displaceable first reflective
element which in a night viewing position is active for
transmitting the light received through the entrance
apertùre, and in a day viewing position is active for
reflecting the light received through the entrance a-
~ perture.
- In a third embodiment, the light separating means
are designed for separating according to wavelength the
` ~ light intended for day viewing and the light intended for
~ 25 night viewing, and thereto comprise a first wavelength-
;~ discriminating element which is fitted to be at least
!i`` substantially transmissive for light within a first
wavelength range which at least substantially corresponds
- ~ to the sensitivity range of the image converter, and to
be at least substantially reflective for light within a
; second wavelength range which at least essentially
. .
corresponds to the visible wavelength range.
In a further embodiment, the output of the image
converter faces the entrance aperture, and between the
entrance aperture and the image converter a second
wavelength-discriminating element is situated, which is
designed to function as a positive reflection lens for
light within a narrow third wavelength range
substantially coinciding with the emisslon peak A of the
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image converter and to be at least substantially light-
transmissive for light within at least a fourth
wavelength range which at least substantially corresponds
to the combination of the visible wavelength range and
the sensitivity range of the image converter, with the
exclusion of the said third wavelength range, and a
focusing reflective element is disposed opposite the
input of the image converter.
; The invention will be explained in greater detail
10 below by a description of preferred embodiments of the
day/night viewing telescope according to the invention
with reference to the drawing, in which the same or
comparable parts are indicated by the same reference
numerals, and in which:
-~ 15 Figure 1 schematically shows a first embodiment of
the day/night viewing telescope according to the inven-
` tion;
Figure 2A schematically shows a second embodiment of
the day/night viewing telescope ac~rding to the inven-
~-; 20 tion;
;~ Figure 2B schematically shows a third embodiment of
~; ~ the day/night viewing telescope according to the inven-
tion; and
Figure 3 schematically shows a further embodiment of
, ~ 25 the day/night viewing telescope according to the inven-
,~ tion.
A number of terms used will now be further
explained.
~,~ Day viewing is understood to mean the observation of
. 30 a s~ene with the aid of light coming directly from the
scene and visible to the human eye.
Night viewing is understood to mean the observation
of a scene in those circumstances in which it is desir-
able to intensify the visible light coming from the scene
and/or to supplement it by converting non-visible light
coming from the scene, generally infrared light, into -
visible light.
For the sake of clarity, only axial beams are shown
` in the figures.
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W092/03754 2 0~ 0i2 ~ PCT/NLgl/0~149 ~
In Figure 1 a first embodiment of the day/night
` viewing telescope according to the invention is indicated
by reference number 1. The day/night viewing telescope 1
comprises a housing 2 with an entrance aperture 3 for
receiving light 100 from a scene not shown. In or before
the entrance aperture 3 an objective system (not shown)
can be fitted for focusing on the scene. In that case the
beams 103, 109 and 116 shown in Figures 1, 2 and 3 will
not run parallel to the axis 5. Although the invention is
not limited thereto, such a day/night viewing telescope
1 can be, for example, a telescopic viewing for a gun.
The daytnight viewing telescope 1 is provided with
an image converter 10 with an input 11 and an output 12,
which image converter 10 can be of a standard type.
;;~ 15 The operation of the image converter 10 is assumed
~- to be known and does not form part of the invention, for
which reason a more extensive description of the image
converter 10 is omitted. It is merely pointed out that
the input sensitivity of the image converter 10 may
~ 20 extend over a wavelength window ranging from visible
- light until into the near infrared, or even into the far
, infrared. In a practical example the image converter 10
is sensitive to light with wavelengths between 600 nm and
^; 1000 nm. The light produced at the output 12 may also
:.,.
; 25 come about through the lighting up of a phosphorescent
layer which has at least one sharp emission peak at a
wavelength A . By way of example, the phosphorescent
layer may contain a phosphor, with a sharp emission peak
at 1 = 543 nm. It is pointed out that the emission peak
in practice is always of a certain width, and that one or
` more subsidiary peaks may occur in the spectrum of the
phosphorescent layer.
The day/night viewing telescope 1 is also provided
with first light guide means 20 disposed opposite the
input 11 of the image converter 10, in order to guide the
light received through the entrance aperture 3, and
- intended for night viewing, to an input of an image
,.. .
converter. In this first embodiment, the first light
guide means 20 comprise a first optical system 21 with
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positive strength positioned between the entrance
aperture 3 and the input 11 of the image converter 10,
the surface area of which system is smaller than the
surface area of the cross-section of the entrance
aperture 3. The part lO1 of the light 100 entering
through the entrance aperture 3 which reaches the first
optical system 21 is imaged (102) by the first optical
system 21 on the input 11 of the image converter 10, and
is thus used for night viewing, while the part 103 of the
. 10 light 100 entering through the entrance aperture 3 which
passes around the first optical system 21 is used for day
~ viewing. The first optical system 21 thus acts as a light
;; separating means.
The day/night viewing telescope 1 is also provided
`:~ 15 with second light guide means 30, in order to guide (105,
107) the light 104 produced by the image converter 10 at
the output 12 thereof to an exit aperture 4 of the
day/night viewing telescope 1. The second light guide
means 30 comprise a second optical system 31 wlth
positive strength which is designed to give the image
produced at the output 12 of the image converter 10 an
object plane which coincides with the object plane of the
scene 100 as observed with the day viewing light 103. In
the example shown, the second optical system 31 is
designed to make the light rays 105 coming from the same
image point run parallel.
Furthermore, the second light guide means 30
comprise a third optical system 32 with positive strength
which is designed to make the light 103 intended for day
viewing and the light 105 produced by the image converter
10, and deflected by the second optical system 31,
~, converge (106, 107) towards the exit aperture 4.
The output image of the day/night viewing telescope
1 observed at the exit aperture 4, for example by means
of an eyepiece system, is a superposition of the day
viewing image and the night viewing image. If the magni-
fication in the optical path of the first optical system
21 up to and including the second optical system 31 is
equal to 1, the day viewing image and the night viewing
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W092t03754 2 0 g ~ 6 ~ ~ PCT/NL91/00149 ~
image match each other exactly, so that, for example,
"during twilight the two pictures can be observed
simultaneously without a disturbing difference in size.
Such a magnification can be achieved by a suitable
combination of the first optical system 2l, the image
converter lO, and the second opticàl system 3l, while the
image converter lO-may be provided with an inverter
("twister") if desired, as will be clear to an expert.
` In the day/night viewing telescope l the light
entering through the entrance aperture 3 is spatially
separated by the first optical system 2l into a part
intended for day viewing and a part intended for night
. viewing, the division ratio being defined by the ratio
between the surface area of the entrance aperture 3 and
~ ~,
the surface area of first optical system 2l. A
consequence of this is that information suitable for
.night viewing is present in the light part intended for
day viewing, but is not used for the former, while
information suitable for day viewing is present in the
light part intended for night viewing, but is not used
for the former. An improvement of the light intensity of
the night viewing image through enlarging the first
optical system 21 results in a reduction of the light
i intensity of the day viewing image, and vice versa.
~i 25Figure 2A shows a second embodiment 40 of the
day/night viewing telescope according to the invention,
having an improved light intensity over the day/night
viewing telescope l, both for the day viewing image and
`~ for the night viewing image. For this purpose, the first
30optical system 21 and the entrance aperture 3 have such
dimensions that all the light entering through the
entrance aperture 3 can strike the first optical system
21. For this purpose, a beam-impander 41 can be fitted,
for example at or near the entrance aperture 3, and/or
35the surface area of the first optical system 21 can be
increased.
. Furthermore, the day/night viewing telescope 40
comprises, in the optical path between the entrance
aperture 3 or the beam-impander 41 and the input ll of
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~ W09Z/03754 2085607~ PCI/NI91il~
the image converter 10, light separating means 50 whicn
. are designed to separate the light intended for day
viewing and the light intended f-or night viewing. For the
` sake of clarity, the ray path for day viewing is shown in
the top half of Figure 2A, and the ray path for night
viewing is shown in the bottom half of Figure 2A.
~:: In the example shown in Figure 2A the light
~- separating means 50 comprise a displaceable first
` reflective element 51. When using the day/night viewing
.:-. 10 telescope 40 the user opts for a night viewing mode or a
day viewing mode by selecting a position of the first
, reflective element S1.
In the day viewing mode the first reflective element
; 51 is positioned in the opti_al path between the entrance
. 15 aperture 3 or the beam-impander 41 and the input 11 o-f
.' the image converter 10, as shown in Figure 2. All the
~,:; light 100 entering through the entrance aperture 3 is
.~ reflected (108) by the first reflective element 51 to a
second reflective element 52, and from there is reilected
(109) to the third optical system 32 for use for day
: viewing in a manner such as described above with
~- reference to Figure 1. In the example shown, the first
:. reflective element 51 and the second reflective element
52 cooperate in order to reflect (109) light rays
incident on the first reflective element 51 from the
:.~ second reflective element 52 past the image converter 10
.. . .
~ to the third optical system 32, f~-- the purpose of being
;~ focused thereby in an intermedi~Le image. The second
. reflective element 52 is preferably a mangin mirror with
: 30 a central recess which is aligned with the entrance
aperture 3.
.~ In Ihe night viewing mode the first reflective
: element 51 is removed from the optical path between the
entrance aperture 3 or the beam-impander 4 and the inlet
: 35 11 of the image converter 10. All the light entering
:. through the entrance aperture 3 then strikes the first
optical system 21 and is used for night viewing in a
:~. manner such as described above with reference to Figure
:. 1.
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:` W O 92/03754 2 0 ~ S ~ O ~ ` PC~r/NL91/00149 ~
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For displacing of the first reflective element 51
and for controlling such displacement, any desired
- suitable means can be used, as will be clear to an
. .
expert. Since the design of said means does not form part
` 5 of the present invention, these means are not described
further here, and for the sake of~ simplicity are not
shown in Figure 2. It is merely pointed out that
switching over from the night viewing mode t~ the day
` viewing mode and back can ta~e place automatically,
'~ 10 without specific action by the user if said means
comprise a control device such as a motor and a light
intensity detector for controlling the control device.
In the day/night viewing telescope 40 the light lOo
entering through the entrance aperture 3 is separated in
time by the light separating means 50 into a part
.
intended for day viewing and a part intended for night
viewing, the separation ratio being defined by the ratio
between the time during which the first reflective
;~ element 51 is in the position associated with the day
viewing mode and the time during which the first
reflective element 51 is in the position associated with
the night viewing mode. Although it is possible for the
first reflective element 51 to be moved to and fro with
a relatively high repetition frequency between these two
positions, in practice the first reflecting element 51
; will be held stationary in one of the two positions. A
- consequence thereof is that in the night viewing mode no
day viewing image is available, and vice versa.
~-; In a third embodiment 60 of the day/night viewing
; 30 telescope according to the invention shown in Figure 2B,
` the advantages of the day/night viewing telescopes 1 and
40 have been combined. For this purpose, the light
' ~ separating means 50 comprise a first wavelength-
discriminating element 53 which is designed to be at
least substantially light-transmissive within a first
wavelength range which at least substantially corresponds
to the sensitivity range of the image converter 10, and
:; to be at least substantially light-reflective within a
second wavelength range corresponding at least
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substantially to the visible wavelength range. An example
of such a wavelength-discriminating element S3 is an edge
filter.
;The operation of the day/night viewing telescope 60
works can be compared to that of the day/night viewing
telescope 40. For light wi'hin the second wavelength
range the first wavelength-discriminating element 53
fulfils the function of the first reflecti~e element 51
. .
in the position associated with the day viewing mode,
while for light within the first wavelength range the
~;~ first wavelength-discriminating element 53 is apparently
not present and is therefore comparable to the reflective
element 51 situated in the position associated with the
~ night viewing mode.
-~ 15In this embodiment of the day/night viewing tele-
scope 60, the first wavelength-discriminating element 53
separates the light 100 entering through the entrance
aperture 3 according to wavelength into a part intended
for day viewing and a part intended for night viewing. In
this case all information suitable for night viewing can
be used for forming a night viewing image, while at the
same time all information suitable for day viewing can be
used for forming a day viewing image.
-~ It is pointed out that the first wavelength range
does not have to coincide exactly with the sensitivity
range of the image converter 10. If the first wavelength
range is less extended relative to the sensitivity range
;~ of the image converter 10, this is, however, accompanied
`~ by a reduced light intensity for night viewing. The same
applies if the transmissivity of the wavelength-
discriminating element 53 within the first wavele~th
range is less than 100~.
:;~ If the first wavelength range relative to the
sensitivity range of the image converter 10 is more
extended towards the visible wavelength range, this is at
the expense of the light intensity for day viewing,
without, however, the light intensity being improved for
- night viewing. It has, however, been found that a loss of
light the wavelength of which is near the upper limit of
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the visible wavelength range, means hardly any loss of
` image and/or colour information for the human eye. A
suitable wavelength-discriminating limit of the
` wavelength-discriminating element 53 is approximately 620
.~ 5 nm.
~ Figure 3 shows a further embodiment of the day/night
- viewing telescope according to the invention which has
-~ the advantages of the day/night viewing telescope 60,
without a beam-impander being necessary, while the
spatial dimensions of the housing can be retained. This
- makes possible a saving in weight and costs. The centre
of gravity of the day/night viewing telescope can also be
placed closer to the exit aperture 4, and thereby closer
to the user. For the sake of clarity, the ray path for
- 15 day viewing is shown in the top half of Figure 3, and the
ray path for night viewing is shown in the bottom half of
Figure 3.
In the day/night viewing telescope 70 the input 11
of the image converter 10 faces away from the entrance
aperture 3. For directing the light 113 received through
the entrance aperture 3, and intended for night viewing,
towards the input 11 of the image converter 10, the first
light guide means 20 comprise at least one focusing
reflective element 71 which is set up opposite the input
11 of the image converter 10, and of which the surface
~ ~ area at least substantially corresponds to the surface
r~ ' area of the entrance aperture 3. The focusing reflective
element 71 is preferably a Mangin mirror with a central
recess which is aligned with the exit aperture 4.
Situated in the optical path between the focusing
reflective element 71 and the input 11 of the image
converter 10 are light separating means 72, comprising a
first wavelength-discriminating element 73 of which the
- wavelength-discriminating action corresponds to that of
.. . .
the first wavelength-discriminating element 53 described
above. The combination of the focusing reflecting element
;
: 71 and the light separating means 72 is configured in
, .
such a way that the light intended for night viewing
forms a focused image on, or at least near, the input 11
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W0 92/037~4 2 0 ~ 5 6 0 ~ pcr/NL9~ e~
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; !~ of the image converter 10.
Disposed opposite the output 12 of the image
converter 10 is a second wavelength-discriminating
element 74 which is designed to act as a positive
~`~ 5 reflection lens for light within a narrow third wave-
length range substantially coinciding with the emission
peak A of the image converter 10, and designed to at
least substantially transmissive to light within at least
a fourth wavelength range at least substantially
corresponding to the combination of the visible
wavelength range and the sensitivity range of the image
converter 10, leaving out the above-mentioned third
wavelength range. The second wavelength-discriminating
element 74 is preferably disposed in such a way that the
ob~ect plane thereof coincides substantially with the
output 12 of the image converter 10, in which the object
. . .
plane is the plane of which the rays after reflection by
the element 74 run in the same way as the rays 116.
In practice, it can be acceptable for the third
wavelength range to differ slightly from the emission
peak wavelength. As will be clear from the description
;- which follows, a greater e~ nsion of the third
wavelength range results, howev~r, in a reduced light
intensity for day viewing, while a smaller extension of
the third wavelength range results in a reduced light
: intensity for night viewing.
`; The day/night viewing telescope 70 operates as
follows: Light 100 received through the entrance
aperture 3 passes (111) the second wavelength-
discriminating element 74 essentially without refraction
and/or loss, with the exception of the light within the
third wavelength range, which is - ~flected (not shown) in
` ~ a diverging man r. The light 111 is then reflected (112)
in a converging ~nner by the focusing reflecting element
` 35 71 to the second light separating means 72.
Light the wavelength of which is greater than the
separation wavelength of the first wavelength-discrimi-
nating element 73, in other words the light 113 intended
` for night viewing, is imaged in focus on the input 11 of
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~ W092/0375~ 2 0 ~ 5 6 0 2 PCT/NI.91/00~49 ~
12
the image converter 10. Light the wavelength of which is
-. smaller than the separation wavelength of the first
- wavelength-discriminating element 73, in other words
light 114 intended for day viewing, is focused by the
light separating means 72 into a real intermediate image
which can be viewed through the exit apèrture 4 with an
eyepiece. `
Light rays 115 of wavelength A emitted by the
: output 12 of the image converter 10, since they are in
the third wavelength range, are reflected (116) by the
second wavelength-discriminating element 74, so that they
:: run in the same manner as the input rays 111 associated
therewith, and are reflected (117) also in a converging
manner by the focusing reflective element 71 to the
second light separating means 72. Since the wavelength
A* is smaller than the separating wavelength of the first
;: wavelength-discriminating element 73, these night viewing
rays are reflected (118) by the light separating means 72
to the exit aperture 4, parallel to the day viewing rays
114 associated therewith, so that at the exit aperture 4
'~ a night viewing image is produced coinciding with the day
viewing image. The combination of the focusing reflective
~ element 71 and the light separating means 72 can in this
; case be configured in such a way that at the exit
. . 25 aperture 4 a real intermediate image is produced which
;:~;. can be viewed with an eyepiece.
. In an alternative embodiment the focusing reflective
-:. element 71 is designed to form on, or at least in the
. ~ immediate vicinity of, the input 11 of the image
.`:. 30 converter 10 a focused image of the light 111 received
through the entrance aperture 3 and the light 116
emanating from the output 12 of the image converter 10
and reflected by the second wavelength-discriminating
element 74 . The first wavelength-discriminating element
73 is designed to be at least substantially diffusely
reflective for light within the second wavelength range,
and can also be flat shaped. For the rest, the way in
. which this alternative embodiment of the day/night
; viewing telescope according to the invention operates is
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~ W092/037~4 2 0 8 ~ 6 0 2; ~ `; PCT/NL91/00149
13
comparable to the day/night viewing telescope 70. A real
night viewing image and a real day viewing image are thus
projected coincidingly on the first wavelength-
~:. discriminating element 73, which real images can be
viewed through the exit aperture 4 by means of an
.~ eyepiece.
The second wavelength-discriminating element 74 is
preferably formed by a holographic optical element. Such
an element can be made with a relatively small transverse
- lO dimension and therefore with a relatively small weight,
: whereby the total weight of the day/night viewing tele-
scope 70 can be reduced, while at the same time the
centre of gravity of the day/night viewing telescope 70
.. : can be shifted in the direction of the exit aperture 4.
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