|Marconi MkIII camera 45° view|
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The Marconi MkIII Image Orthicon camera
was available with either 3" or 4.5" tubes. The tube was installed
from the front of the camera, the complete turret assembly could be
removed by slackening the 4 large bolts in each corner of the turret
housing. In operation the irises on the lenses were preset to the same
value, say f5.6, this gave the same depth of field for each lens and
the exposure was controlled by means of a motor driven graduated neutral
density filter. The turret was operated by a crank handle at the rear
of the camera and the "beer pump" handle moved the tube and
its yoke for focusing. It was possible to move the focus control to
the other side of the camera, but I have only seen this done once.
First the large black knob in the dead centre of the turret, releases the turret plate with the 4 lens positions and lens fixing clamps. This is all that needs to be undone to remove the turret plate, It may be stuck in due to corrosion of the alloy. If you remove this it will expose the filter wheel and behind it the rotating variable density filter. Be extra careful with this as it breaks easily and is utterly un-replaceable. It is not necessary to remove the the turret plate to remove the complete turret assembly.
Make sure that the turret plate is either secure or removed. Undo the 4 large chrome bolts in each corner and it should just pull forward. The rubber gasket is fixed to the camera body so you may have to run a sharp thin knife around between the rubber and the turret assembly. There is a 18 pin (I think) Plainton connector that should just separate, I have never known that to stick and there is a mechanical linkage that should just separate (Turret Drive). Lever carefully if you have to and try jiggling it up and down.
Good luck and be careful with the ND filter.