Why has Philips made a flat spot in the middle of the film gate of the Norelco AA projector.
For me and some other technicians it was a mystery why there was a flat spot in the film gate exactly on a place where we expect maximum stability of the image during projection.
The flat spot gives the impression that the opposite is accomplished.
A very nice conversation I had this summer with mr. Cas Kessler, a former employee of Philips and fellow worker of mr. Kotte gave me an explanation for the mystery. Mr. Kessler has reached the age of 92 years but still in very good health and because he was also a friend of mr. Kotte he knows a lot from that period.
When Philips got in the mid fifty’s the order to design a projector for 70 MM projection the first thoughts of the designers was an expansion of the existing FP5 35mm projector which was produced for many years with great succes.
But also for them the 70mm format was a unknown territory. And of course the handling of the print material was in principle the same as for 35mm except that it was twice as wide. This size revealed a till then unknown problem: “heat flutter”.
At that time every cinema used carbon arc light source and cold light mirrors were not availeble in the fifty’s.
Especially in the US, were some screens were tremendous and therefor the heat-radiation on the print was that high, so deformation of the image made it impossible to focus.
This was a very big problem. They have tried with extreem ventilation but the time was to short to get any effect and besides that the heat energie came from radiation. More excessive pressure on the print made the problem even worse.
At the end the designers discovers that if they give the film more space to deform, the problem got smaller. So to reduce the pressure on the film in the gate, where all the radiation takes place, the “heat flutter” is less when the film gets more space instead of less.
