This camera provides a highly adaptable "platform",
which can be used with almost any ordinary SLR camera lens. There will be
many different ways to arrive at a similar result, depending on your own
particular requirements. For example, you could chose a plastic box to
save weight.
The internal construction of the camera is extremely
simple. The XX1332 intensifier tube possesses flat input and output
windows. Formed from a high resolution fibre-optic bunch, these windows
provide a focal plane which lies at the tube surface, making application very
simple.
The housing
Our camera is built into a 215 x 115 x 75mm diecast aluminium
box. This is rigid, light-tight, and easy to work with, but certainly
weighs more than a plastic box.
The MK2 intensified camera, with a 135mm F2.5 Pentax
lens.
Power connections are via a pair of colour-coded 4mm
binding posts at the rear. Video output is via a standard BNC
connector. The robust aluminium case also has a tripod mounting
fitted underneath.
The lens mounting shown in detail below can accept Canon
EOS lenses, or with an adaptor (as here) Pentax screw-threaded
lenses. The lens mounting is one of the design options that should
be considered early on. We would not recommend the use of
"c-mount" lenses because they produce an image that is too small
for use with the XX1332.
The lens
At the input side of the intensifier, the image produced by the
main objective lens should land on the input window of the tube. If you are using an
ordinary camera lens (highly recommended), the surface of the tube will lie
where the photographic film would normally have been. Thus the ideal
distance from the lens mounting to the intensifier window can be determined by
examination of the camera which donated the lens!
We wanted our camera to use the bayonet-fit Canon EOS
lenses. This poses an interesting mechanical problem. How do you
attach the lens to the box?
The solution is remarkably simple. There is a camera
accessory available known as an "extension tube", which is designed to
fit between the SLR lens and camera body. The purpose of this device is to
extend the close-up capabilities of the lens, but this is not why we are
interested. We are interested because the extension tube is a small
aluminium barrel, with a lens mounting on one side and a camera mounting on the
other side. If you chose carefully, you should be able to get one where
these mountings are screwed on, and hence can be removed. We found the EOS
extension tubes supplied by Jessops are ideal for this purpose.
The MK2 intensified camera, front view (lens adaptor).
This photograph shows the Jessops EOS extension tube
fitted to the front of the camera housing. The rear part of the
extension tube has been removed, and in it's place is an aluminium plate,
which is itself screwed to the front of the housing.
This very simple arrangement provides a stable and
secure mounting for the lens, and also allows rapid lens swaps!
This arrangement, as-is, will accept lenses from the EOS
15mm fish-eye to 500mm mirror lenses. Of course you can use almost
any zoom lens too.
The CCD
At the output side of the intensifier, an image is produced
which is approximately 40mm in diameter. Manufacturers of
"professional" intensified cameras would lead you to believe that
coupling the intensifier to a CCD is a difficult thing to do. Some very
exotic techniques have been developed for doing this, including the use of fibre-optic
plates. But don't worry, it's really simple with the XX1332!
Our camera was built using a completely ordinary PCB camera
module, with integral 4mm lens. Adjustment of the lens can bring objects
into focus that are only a few millimeters from the lens. After a few
simple experiments focusing the lens onto a ruler, it is a simple matter to
adjust the PCB camera so that the whole (video) image is filled by the output
window of the intensifier tube. Further experimentation clearly
demonstrates that a better image is produced if the PCB lens is changed to a
longer focal length of 8 or even 12mm. This reduces the effect known as
pin-cushion distortion, and helps to keep the whole image correctly in focus. We would recommend the use of a 12mm
lens, which is readily available from good CCTV suppliers.
The MK2 intensified camera, CCD (PCB camera).
This photograph shows the PCB camera mounting bracket
and the relative position of the intensifier tube output window.
This arrangement currently uses a 4mm lens, but tests
have demonstrated that significant benefits result from the use of longer
lenses. A 12mm lens is our recommendation.
The mounting of the PCB should place the lens in the center
of the intensifier window (center-axis), and at a distance which
results in the entire video image from the CCD being filled by the output
window of the intensifier tube.
There is a school of thought which says that the coupling of the
CCD to the intensifier window must be highly "efficient". Our
own tests with the XX1332 have proven conclusively that this is not a problem,
since even moderately sensitive PCB cameras are able to detect the "sparklies"
which are produced by the intensifier under conditions of zero
illumination. If your finished camera can do this, there is no further
improvement to be had. The XX1332 intensifier tube has a very high gain,
which is the reason why a little inefficiency at the output end is unlikely to
affect the overall performance.
We recommend the use of a good quality "HAD" or
"Super HAD" PCB camera, which are now commonplace and
inexpensive. You can choose PAL format or NTSC, the XX1332 intensifier
will work equally well with both formats. It makes sense to use the
highest available resolution, because the XX1332 is capable of extremely high
resolution. The CCD will usually be the limiting factor which determines
the overall resolution of the finished camera.
Most PCB cameras are designed to operate from a 12V power
source.
The XX1332 image intensifier
The image intensifier tube must be mounted securely, and must
certainly not be free to move around. This is important, because the stability of
the focusing arrangements is critical to the image quality and resolution of the
completed camera. Our camera uses a combination of fixed supports, springs
and foam. It is important that the mounting of the intensifier tube does
not put undue stress on the tube housing, and must not make physical contact
with the tube windows.
The MK2 intensified camera, overview.
This photograph gives an overall view of the XX1332
mounting, and relative positions of lens mount and CCD.
The XX1332 intensifier tube requires a power supply of
6.5V. Our camera incorporates a voltage regulator such that the
complete camera can be operated from standard 12V power sources.
Results
The MK2 camera as shown above provides superb results.
Fitted with a wide-angle lens it can easily capture meteors down
to ~magnitude 7, or if your interest is surveillance, it gives a crystal clear
view in conditions where the unaided eye struggles to cope.
Fitted with larger lenses, the results are absolutely stunning.
We have also tried 28-200mm zoom lenses, with predictably beneficial results.
