Fujica P300 Single-8 Cine Camera Manual Exposure Mod

The late 1960s/early 1970's Fujica P300 Single-8 cine film camera has a fully automatic exposure system that relies on a light dependent resistor (LDR). It has no manual override, which was a problem for the one I have that had a failed LDR. The camera was otherwise in very good condition, and I want to be able to shoot some film with it.

After some testing I found that I could make the camera fully manually controlled by replacing the LDR with a potentiometer. 

A small 9mm 50K pot with a long plastic shaft (like this one) fits nicely in the space taken by the LDR. Some resistors have to be removed from the meter circuit. The aperture can be controlled with the camera held up to the eye. Power is still required for the aperture to function, but it is not necessary to have the exact 2.7V provided by the PX14, so modern 2x 1.5V work fine.

I designed a mount for the potentiometer based on the dimensions of the LDR holder, and a battery holder for the light-meter circuit to allow use of modern LR44 cells in place of the mercury PX14 battery. 

The mount was printed in ABS on the Prusa MK4 at 0.1mm layer height as the print incorporates a screw thread for the original metal retaining ring. The potentiometer clips into the mount after soldering it to the LDR wires. Some glue was used to hold it in place.

Full details and teardown instructions are in the PDF file. It does mean dismantling the camera significantly - so proceed with caution at your own risk if you decide to attempt this mod!