Image intensifier attachment for attachment to the front lens of a television camera

In order to increase the sensitivity of television cameras so as to allow the cameras to operate in low level light, an image transformer attachment, in the form of an ancillary image intensifier, is provided for attachment to the objective lens opening of the camera. The attachment includes a cylindrical housing containing one or more proximity-focus image converters or intensifiers which are optically connected to the pick-up tube of the camera by a fiber optics cylindrical block. The housing includes an annular disk screwed into its input end, which disk has an opening for the objective lens of the camera and which disk urges a resilient ring against the image transformers to bias the intensifier and fiber optics block against the pick-up tube of the camera. At its output end, the camera has another annular disc with a threaded projection thereon, which projection is received in the threaded opening normally holding the objective lens of the camera to retain the attachment housing in fixed relation with respect to the camera while the first disk is screwed into the housing.

BACKGROUND OF THE INVENTION 
To date, it has been the custom in low light level television cameras to 
provide an image intensifier which is coupled through fiber optics and 
located in front of the television camera pick-up tube. This configuration 
necessitates special modification of standard television camera housings 
to accomodate the attachments. Moreover, these modifications require 
considerable effort in order to convert standard cameras into low light 
level cameras. Accordingly, there is a need for an image intensifier front 
lens attachment which can optionally be attached to normal television 
cameras in order to expand the sensitivity thereof without modifying the 
camera structure. 
In utilizing image intensifiers with television cameras, or any type of 
camera in which photoelectric effects are a consideration, the 
intensifiers should be shielded and electrically isolated. This is because 
the intensifiers generally utilize voltages in the range of 1500 . . . 
4500 volts which can adversely affect other equipment if allowed to leak. 
While these considerations are especially pertinent to television cameras 
they also apply to other types of cameras and photoelectric devices. 
SUMMARY OF THE INVENTION 
In view of the foregoing considerations, it is an object of the instant 
invention to provide a new and improved means for converting television 
cameras to low light level cameras. 
In view of this object, and other objects, the instant invention 
contemplates an image transfer attachment for television cameras wherein 
the attachment is positioned between an objective lens exterior of the 
housing for the television camera and a pick-up tube within the housing of 
the television camera. The attachment includes an image intensifier 
mounted in an attachment housing wherein the attachment housing has an 
input and an output end, the input end having an opening therethrough for 
receiving the objective lens and the output end having an opening for 
alignment with the pick-up tube. The attachment is rigidly attached to the 
television housing and a resilent member is disposed between the input end 
of the attachment housing and the image intensifier. A cylindrical fiber 
optics block projects through the opening in the output end of the 
attachment housing and between the image intensifier and pick-up tube. The 
resilent member biases the image intensifier and cylindrical fiber optics 
block toward the pick-up tube so as to hold the cylinderical fiber optics 
block against the pick-up tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 of the drawing, an image intensifying, front-lens 
attachment 1 is shown screwed into an opening 2 through a front face 3 of 
a housing or casing for an image processing apparatus, which in the 
preferred embodiment is a television camera. The opening 2 normally 
supports the objective lens of the television camera. The attachment 1 
includes a cylindrical attachment housing having an annular disk 4 at the 
output thereof and an annular disk 6 at the input end thereof. A 
cylindrical mantel 7 connects the two disks 6 and 7 to form the housing. 
Two proximity-focus image transformers, in the form of cascaded input and 
output image intensifiers elements 8 and 9, respectively, are disposed 
within the attachment housing and are optically coupled with a front plate 
12 of a pick-up tube 13. This optical coupling is effected by a 
cylindrical glass fiber optics block 11. The fiber optics block 11 is 
preferably adhered or otherwise secured to the output image intensifier 
element 9 to form a unit therewith. 
The glass fiber optics block 11 is fiber coupled with the output fiber 
window of the image intensifier 9 and preferably forms a single unit with 
the image intensifier 9. The glass fiber optics block 11, does not 
increase the target capacity of the pick-up tube 12, consequently, 
signal-to-noise ratio deterioration does not occur due to the coupling 
therebetween. 
The structure of each of the elements 8 and 9 is shown in the schematic 
prior art illustration of FIG. 2, wherein a pair of plates A and B are 
separated by a spacer C to form an evacuated space D. Photoelectric 
coatings E and F are deposited on both plates A and B and a potential of 
up to 21,000 VDC is applied across the gap therebetween. Cascaded image 
intensifier tubes consist of a clear input window, bearing the first 
photocathode; all other windows are of fiber plates for coupling from 
stage to stage and to the fiber block at the output. Since the vacuum in 
space D is on the order of 10.sup.-8 torr, when photons strike coating E 
electrons will be emitted therefrom and accelerated by the electric 
potential toward the coating F. When the electrons strike the coating F, 
numerous photons are emitted from the coating F thereby intensifying 
emitted light by increasing the number of photons emitted from the element 
for each photon striking the element. 
The disk 4 has an external thread on an annular projection or collar 14 
which projection is screwed into a complementary thread in the opening 2 
of the television camera housing 3. Normally, the opening 2 accomodates 
the objective lens of the television camera, which lens is removed when 
the attachment 1 is mounted to convert the camera to a low light level 
camera. The input end annular disk 6 has an opening 16 with an inside 
thread 17 into which a recording objective lens (not shown) is screwed. 
The opening 16 is preferably large enough to accept high-power objective 
lenses. The cylindrical mantel 7 has threads for fastening the disk 6 
therein and an opening 18 therethrough for passage of operating voltage 
cables 19 for the image intensifiers 8 and 9. The disk 6 is retained in 
the mantel 7 by screw threads 20 while the disk 4 is fastened to the 
mantel by machine screws (not shown) to form a rigid structure therewith. 
In order to provide good optical contact between the block 11 and the 
fiber disk 12, a resilent annular element 22 which may be, for example, a 
foam rubber gasket or perhaps individual foam rubber components, is 
positioned between the front annular disk 6 and a potting casing 21 within 
which the image intensifiers 8 and 9 are contained. 
In securing the image intensifiers front lens attachment 1, in accordance 
with this invention, to a television camera, the disk 4 is first screwed 
into the opening 2 until a portion abuts the camera housing in order to 
rigidly position the disk 4 with respect to the camera housing. The image 
intensifier component units (consisting of image intensifiers 8 and 9 and 
the potting casing 21, plus the fiber optics block 11) is then inserted 
through the opening in the center of annular disk 4 so that the fiber 
optics block 11 abuts the fiber input window 12 of the pick-up tube 13. 
The cylinderical mantel 7 is then aligned with the annular disk 4, slipped 
thereover and secured thereto with machine screws. Annular disk 6 is then 
screwed into the cylindrical mantel 7. Consequently, the image intensifier 
components 8, 9, 21, and 11 are supported in alignment with the disk 12, 
on the pick-up tube 13. In order to keep the fiber block 11 in radial 
position, the diameter of the fiber optics block 11 is slightly less than 
the opening through the annular disk 4. Moreover, there is a slight space 
between the potting housing 21, and the annular disk 4 when the block 11 
is against the disk 12. All axial contact between the various image 
intensifier components 8, 9, 11, and 21 and the annular disk 4 is 
therefore avoided, and the image intensifier components are suspended 
between the resilient ring 22 and pick-up tube 13. 
In order to prevent twisting of the image intensifier unit (components 8, 
9, 11, and 21) during assembly as the annular disk 6 is rotated, a pin 23 
is provided which extends between the image intensifier unit and a short 
slot 24 in the mantel 7. If it is desired to insert an intermediate disk, 
the intermediate disk can also be configured in such a manner that it is 
prevented from twisting both with respect to the image intensifier unit 
(components 8, 9, 11, and 21) and the disk 6. 
If it is desired that the image intensifier unit contain only one of the 
image intensifiers 8 or 9, the front lens attachment housing can be made 
shorter. If needed, to produce a high voltage out of a low battery voltage 
a free swinging oscillator and high voltage multiplier (not shown), which 
produces the high voltage for the operation of the image intensifiers 8 
and 9 can be accomodated in the space between the disk 6 and the amplifier 
unit. Because the housing of the front lens attachment 1 consists of metal 
or metalized plastic, there is no danger that a moire pattern interface 
will develop in the image of the camera monitor if an oscillator is 
included. 
It would be within the scope of this invention for each individual image 
intensifier to be cast into a voltage multiplier ring. For the purpose of 
further shielding the entire outer surface of the image intensifier unit 
(consisting of elements 8, 9, 11, and 21), the entire unit is coated, if 
desired, with an electrically conductive coating. The coating is connected 
to ground and is optically transparent in required zones at axial ends of 
the elements where light transmission is necessary between components of 
the image intensifier unit and the television camera. 
Preferably, but not necessarily, the casing 21 includes a transformer 30 
sealed therein with potting material. While the transformer 30 is 
illustrated as a toroidal transformer, it may have any convenient 
configuration. As is seen in FIG. 2, the transformer 30 is preferably used 
to step-up voltage from a battery 31, which may have an output of for 
example 1.0-2.6 volts, to a voltage level which may be as high as 
approximately 21,000/or 42,000 volts D.C. if necessary or desired. 
The attachment of the aforedescribed proximity-focus image intensifier, 
according to the instant invention, is advantageous because in coupling 
the image intensifier to the pick-up tube, a precise coincidence of two 
optical axises need not be taken into consideration due to the fact that a 
proximity focus image intensifier has absolutely no shading (normal 
inverter image intensifier have pronounced edge shading due to plane 
concave fiber window). Moreover, the front lens attachment, according to 
the instant invention, is not restricted to one image intensifier but may 
be equipped with two or more image intensifiers. Consequently, the 
sensitivity of the camera can be increased to the point where the camera 
can be used as a low light level camera. In practice, intensification 
values in the range of 1 to 35,000 fl/fc (gain of 14 aperture stops) is 
attainable. Through the use of a quartz or saphire disk as the input 
window of the image intensifier, a spectral range from ultra-violet 
wavelengths to near infra-red wavelengths is possible. 
While the attachment 1 is disclosed in combination with a television 
pick-up tube 13, the attachment may be used with other optical, 
photographic or photoelectric devices, systems or image receptors. For 
example, the attachment 1 or the intensifier unit (components 8, 9, 11, 
and 21) by itself could be used with astronomical instruments and cameras 
to intensify the weak light arriving from stars, planets, comets and the 
like. 
While the aforedescribed embodiment is illustrative of the instant 
invention, the invention is to be limited only by the following claims.