Build complex toys and simple tools
by Tony Karp
Doing the impossible - Part 2 - The challenges
zoom lens - Doing the impossible - Part 2 - The challenges -  - The Godfather - computer controlled zoom lens - - - art  - photography - by Tony Karp
This is what the Angenieux 25 - 250mm zoom lens looks like in its unmotorized form. It's quite large and quite heavy, weighing over ten pounds. The two rods are attached to the camera and run underneath the lens to support its weight. This is the bare lens with no zoom control attached.
Here are some of the design and philosophy issues that were involved in the design and building of the computer-controlled zoom lens used to shoot the opening scene of The Godfather.

Where no man has gone before - It would have been nice if someone else had already built a computer-controlled zoom lens. Then I would have had some guidance, and could have just worked on building a better model. But no one had. I would be the first. In fact, my zoom control was probably the first piece of computer-controlled equipment ever built for motion picture use. So, Like Captain Kirk, I ventured forth.

Artistry - There were some controls for zoom lenses available at the time, but they were very simple. A typical one was fitted to a small handheld box with a little lever that did the actual controlling. Push the lever a little bit and the lens zoomed forward slowly. Push the lever a little bit further and the lens zoomed faster. Push the lever in the opposite direction and the lens zoomed in the opposite direction. That was it.

So it's no surprise that anyone who could produce exactly the zoom that the director or the cinematographer wanted was highly sought after. Zoom lens operators might be booked several pictures in advance. They were considered as artists for this ability. But even with all of this skill, the best that could be hoped for was just an approximation of the desired zoom. The use of the zoom lens in motion pictures was limited because of these problems.

Repeatability - It's one thing to do a zoom, but it's something else entirely to be able to repeat exactly the same zoom again and again, take after take, until the director is satisfied with the result. The characteristics of an ideal zoom would be to hit the start and end points accurately, and to make sure the zoom would take exactly the right number of seconds, every time.

With the old zoom controls, you would fiddle with the little lever until the starting point for the zoom looked pretty good, then mark that on a piece of tape around the lens. Then repeat the process for the framing at the end of the zoom, and make another mark on the tape. Then fiddle countless times until you got the right time for the zoom between the two points and make a mark on the zoom control showing how far to push the little lever. It was a long and complicated process to set up any but the simplest zoom.

Room at the top - This was always a sore point with both the director and the cinematographer. They wanted to be able to set up the zooms themselves. The framing at the beginning and the end of the zoom is critical, as is the time it takes to get between the two points. You would rehearse the actors multiple times and then measure the time with a stopwatch. This would tell you how long the zoom should take if it was going to match the speech.

Wouldn't it be nice if the director or cinematographer could just look through the camera, set the start and end points for the zoom, and then, somehow, set the time that the zoom should take? Wouldn't it be nice if the zoom could be repeated any number of times, producing exactly the same zoom at the touch of a button?

For this, you needed a computer, and this is where I was headed.

Infinite speed range - It would be nice if the zoom control could do a very fast zoom -- say half a second from end to end. And it would be nice if the same control could give a zoom that went on for minutes, as in the opening scene of The Godfather.

This is a problem I didn't even think about when I started. The existing zoom controls had a very limited speed range. You might have a range, for a full zoom, from several seconds to about thirty seconds. Zoom lenses required a lot of torque to turn them, and this required small, powerful motors. But motors of this type had a limited range of speeds.

I would be using a similar motor in the zoom control I was building, and I would have to find a way around this limitation.

Soft start and stop - This a little something extra. Instead of an abrupt start and end to the zoom, it would be nice to have a soft start and stop. If done properly, the start would be imperceptible, and the end of the zoom would be equally smooth. There should be an adjustment for this softness, from none to maximum.

Computer - In 1968, computers that could do the sort of real-time processing that would be needed to control a zoom lens were the size of a refrigerator, drew thousands of watts, and needed very complex assembly language programming. Obviously, I would be headed in another direction. In the end, I designed a computer to control the zoom lens. It weighed less than two ounces, measured less than 3 x 4 inches, and drew only a few thousandths of a watt of power.

Motor control - The motor control would have to be solid state, using minimum power for the longest battery life, and be capable of driving the zoom lens over an infinite speed range.

Portability - Easy to carry and easy to set up - The control unit that would program the computer would be handheld and should weigh about a pound. The power unit with the batteries and the motor control circuits should weigh less than ten pounds. On the movie set, the system should be easy to set up and easy to break down at the end of shooting. In addition, there would be cables hooking the system together. There should be no way to put things together incorrectly.

The lens with its attached motor, the computer unit, the power unit, and all cables should fit into a padded, easy-to-carry container that would be as rugged as any piece of movie equipment.

Interface - Here, in the twenty-first century, computer interfaces are very advanced, with touchscreens, mice, and computers that respond to human speech. When I built the zoom control, there were no computer interfaces, other than a primitive display terminal or a Teletype terminal. The interface for the zoom control would have to be easy to use and shouldn't require any special training. It would have to be intuitive, so a director or cinematographer could easily program even a complex zoom.

Quite a requirements list, and there would be many more hurdles along the way.

Part 3 will tell about some of the solutions to these problems.
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