MK3 Intensified Camera

The MK3 intensified camera is not, as you may have expected, an advance on the MK2.  It is just different, and in fact not so useful because the lens is of fixed focal length.  This description will make much more sense if you read the description of MK2  first.

The original sight

The MK3 was an attempt to produce an intensified camera with the absolute minimum of effort, and to this end, it is built using the body and main lens of a military night vision periscope.  The principal advantage of doing this is that the intensifier tube is robustly mounted, and the main objective lens (which incorporates an adjustable iris) is also present and already in the correct place relative to the intensifier tube.  So no effort required at that end!

This photograph shows a side-view of the original military night-sight, which is actually a periscope system for armored vehicles.

At the top you find the objective lens, a prism, and an adjustable iris.  Underneath this, in the main body of the device, the XX1332 image intensifier tube is mounted vertically.  There is also an iris control and power switch lever, a voltage regulator and fuses.  Under this, in the base of the unit, is the panoramic eyepiece assembly.

The eyepiece is large, and provides both eyes with a simultaneous view of the intensifier tube output window.

  

The modifications

The night sight shown above was partially dismantled by removing the face cushion and entire eyepiece assembly.  This was necessary because the CCD (PCB camera) is to be mounted where the eyepiece is normally fitted.

This photograph shows the night sight with face cushion and eyepiece assembly removed.

The output window of the XX1332 image intensifier is exposed and clearly visible in the base of the unit.

The objective lens was also removed for this picture, but later re-fitted.

Once the unit is dismantled, a standard diecast aluminium box is fitted to the base of the unit where the eyepiece assembly was removed from.  It is possible to attach the box securely using the existing eyepiece screw positions.

The lid for the diecast box has the power connections (standard 4mm posts), video connector (BNC), and the PCB camera attached.

This photograph shows the diecast box in position, and the PCB camera mounted to the lid of the box.

The position of the camera must be central to the output window of the intensifier tube.

Please see the description of MK2 for a discussion of PCB cameras and lenses.

Once the components are mounted and the PCB lens has been adjusted, the box lid can be fitted and the camera is complete.  Our camera has the power for the intensifier routed through from the newly fitted box.  It is entirely possible to do this the other war round, and supply the PCB camera from the main sight power connector.

The completed camera

This photograph shows the completed camera, resting on it's side.

The whole init is powered by 12V via the colour-coded 4mm posts mounted at the base.  The original iris control lever is retained, and provides a useful range of adjustment.

Results

The results are excellent, with clear views in almost any lighting condition.  Easy capture of meteor trails down to magnitude ~7.0, and excellent night scene views.  However, there are two problems.

The fixed length lens (actually 66mm) is a serious limitation when compared to the flexibility of the MK2 camera with it's interchangeable lenses.  For some applications this doesn't matter, but if you would like the flexibility this could be a problem.  There is no simple way to provide an adjustable focal length on this unit.  If you need this feature, look again at the MK2!

The second problem is that the image is mirrored.  This occurs because there is a prism at the objective end which reverses the image, but there isn't one at the other end to reverse it back again.  This can be corrected in two ways.  Firstly, you could fit a prism between the PCB camera and the intensifier output window.  The mechanics of this could be awkward.  The second way is to obtain a PCB camera that has selectable mirroring, they ARE available, because some security applications make use of cameras that view via a mirror (it's sometimes an anti-vandalism feature).

We have looked into the idea of removing the prism at the objective lens end, and this is not a straightforward task, in either the mechanical or optical sense.

Conclusions?

Well this was a fun idea, but the mirrored image was irritating.  This was why we tried the MK4 concept.  Much better.