Inventor of Auto Focus Ed Todoroff

Nov 15, 2010 -- Fifty year anniversary of autofocus for slide projectors

I am writing on the day of the 50th anniversary of autofocus, invented by my father Edward Todoroff (1921-2004). He told the story to friends and family of coming up with a method to autofocus a projector when he worked for Sawyer's, the company that made Viewmaster in Beaverton, Oregon. I recently discovered his log book that documented his invention.

Before World War II Ed Todoroff graduated in Engineering from Benson Polytechnic in Portland, Oregon. The war started before he could continue studies, and he worked most of his tour in the technical aspects of photogrammetry. Based with the China Burma India Theater in Dehradun, India, he converted aerial photographs to maps for many areas of the world that had never been mapped before.

By 1960 Todoroff was working at Sawyer's as a design engineer on their model 500 slide projector. He went to the chief engineer at Sawyer's with a novel way of achieving projector autofocus. The invention was immediately deemed too expensive, even though the parts were a pilot project to prove the concept, not to achieve production efficiencies.

At Sawyers my dad's boss, who was more of an accountant than an engineer, rejected the invention. Dad had an actual working prototype, and the cost of the parts were too much for the boss, who did not seem to understand that a production version would be way cheaper than the prototype. Todoroff was told to forget about auto-focus. It was one of many encounters that left my dad forever disappointed as an engineer about company accountants like this one, who stopped the invention of auto-focus from being used or patented by Sawyer's.

A few years later, Sawyer's had to pay large amounts of money to Kodak for the license to use Kodak's autofocus invention and patent.

If anyone knows of an earlier invention of autofocus, please let me know. Here are the exact notes from my father's log book.

Nov 15, 1960

This is to disclose an invention relating to slide projectors and the like and explain a method of automatically focusing the projector to compensate for inaccuracies due to the position of the transparency not being identical from slide to slide in relation to the projection lens system.

It is known that the film plane of the transparency should be identical, in the slide projector, in relation to the lens system, when the projecting distance is fixed for the showing of a number of slides. Any device that could measure the distance from the film plane and projecting lens and compensate, that is, either move the film plane or projecting lens to maintain a fixed distance, as predetermined by the projecting distance, that is from projector to the screen, would accomplish this automatic focus.

However, it is easily seen that any device mechanical in nature would not suffice since basically the film is not perfectly flat in the case of sandwich mounted film transparencies in frame type mounts, and in all probability could not sense the film plane position without getting into the optical path of the light source and cast shadows.

Also the device must be compensating, in effect, to measure the average distance due to waviness in the film itself. With this in thought, I propose a means of measuring this distance and compensating for the film position by the use of high frequency sound (above the audible range).

As seen in drawing no 1, the lens supporting barrel would have a clear glass face fastened to the end nearest the film transparency. On the either side of the optical axis and out of the way of the project image would be a sound transmitter and receiver arranged in such a manner that sound waves would be deflected back and forth between the film plane and the end of the lens barrel. By focusing this beam of sound from the transmitter so that it will meet with the receiver a null point could be obtained.

Should this distance change from the end of the lens and film plane, the resultant focused beam would not fall on the receiver but would face to either side. By either signal strength or the use of two concentric receivers, this distance could e corrected by moving the lens barrel until the null point was obtained; thus correcting to its original distance between film plane and projecting lens. By varying the position of the receiver or transmitter, projected distance can be set up as determined by the projection distance from lens to the screen. All movement of the lens system (or film plane) could be done by a servo circuit tied into the transmitter and receiver apparatus so that a motor (electric) would be activated to correct and maintain the preselected distance, by moving the film plane of projecting lens.

Edward J Todoroff    Nov 15, 1960   Witnessed: Robert E Lock Nov 16, 1960

I have read the above and understood the invention and it application.

11-16-1960 Frank (signature illegible)

Original pages from the 1960 engineering log book are listed below:

Articles and photographs copyright Gary Todoroff. For licensed use, call (707) 445-8425 or contact him by email.