One product of the design experiments did not make it to manufacture.
For many years, an experimental component for the FE, the size of a match head, has been lying in a drawer of my desk.
This component was an integrated circuit package intended for the FE, and known because of its shape as the "boomerang."
To describe the circumstances behind this, I had better start by talking about the photo sensors used for light metering.
Nippon Kogaku adopted a SPD (silicon photodiode) as the photodetector for the EL2 and the F2 Photomic SB, and a GPD (gallium arsenide phosphide photodiode) for the FM.
Compared with the CdS elements previously used, these have a much faster response, and good characteristics, but the output current is much smaller.
A slight imperfection in the circuit insulation, and the current can leak away, preventing accurate light metering.
Very special care had to be taken, therefore, in assembling the circuit to make sure that the connection between the photo sensor and the control chip's input terminals was properly insulated and protected from influence of external noise.
To prevent leakage currents and protect from influence of noise, we wanted to make the connection from the photo sensor to the control chip as short as possible, and seal it within the circuit board. "Well," we thought, "In that case why not put the photo sensor inside the control chip package ?"
Meanwhile, there had always been two (2) photo sensors, one on each side of the viewfinder eyepiece, but we had a plan to replace these by one element above the eyepiece.
The integrated circuit package mentioned above was an experimental result of this plan.
The boomerang-shaped package was arranged on the eyepiece side of the viewfinder pentaprism, extending to the side from over the eyepiece lens.
The leads from the photo sensor entered two (2) holes arranged vertically on the top of the package, and were soldered.
The integrated circuit chip was enclosed in the hollow underneath, with a metal covering seal.
The package had a multilayer construction, with internal interconnects between the photodetector and integrated circuit chip, and then the terminals of the chip were connected from the back of the package to the flexible printed circuit (FPC).
If implemented this would have been a revolutionary design.