Build complex toys and simple tools
by Tony Karp
Doing the impossible - Part 3 - The solutions
printed circuit #1 - - Doing the impossible - Part 3 - The solutions -  - The Godfather - computer controlled zoom lens - - Tony Karp, design, art, photography, techno-impressionist, techno-impressionism, aerial photography , drone , drones , dji , mavic pro , video , 3D printing - Books -
Here's that actual computer from the zoom lens control. It's an analog computer, with twelve operational amplifiers, precision resistors (.001% accuracy), and assorted capacitors, all mounted on a card measuring two and a half by four inches and weighing less than two ounces. When used for its specific role, it will outperform a standard computer many times its size.
Here are some of the solutions to the puzzles that were involved in the design and building of the computer-controlled zoom lens used to shoot the opening scene of The Godfather.

Grokking the system - There is an ancient story of the butcher whose knife never got dull. As he cut, he sensed how to move the blade so that it would cut through the meat, avoiding the bones and cutting without resistance. In the Zen aspect, this happens unconsciously, driven by a deeper, inner understanding.

This is how you have to think if you are going to solve impossible, intractable problems -- you have to "grok" the system you are working on, until you become as one with it. You have to study the problem, understand it, then let go and allow your subconscious to seek the solution. Designing and building the zoom lens was an exercise in the Zen of design.

Designing the computer - Let's start at the beginning. In moving the zoom from point A to point B, there are two things to consider. You can control the speed the lens is moving, or you can control its position. The zoom control would have to do both. You have to be able to set the start and end points and how long it will take to get between them.

While it is relatively easy to control the position of the lens, measuring its speed accurately, especially at very low speeds, is quite difficult. Suppose there was a way to control the speed of the lens without actually measuring its speed? Sounds very Zen.

As a start, let's say that you move an object at a constant speed. When you do this, its position also changes at a constant rate. If you draw a graph of this, it's a straight line, showing the position at each point. If we turn the problem around and look at it from 90 degrees, you can control the speed of the lens by just moving it to the correct position as it changes with time.

Now we can throw out the requirement for measuring the speed and replace it with measuring the position, which we needed in any case. All we have to do is calculate where the lens should be at any point in time.

This breakthrough greatly simplified the problem and increased its do-ability. It's an example of how to solve an impossible problem by deepening your understanding to the point where you can restate the puzzle in a solvable form.

Now all I needed was a computer that would generate the information needed to control the position of the lens

There are two basic types of computers. Digital computers are what's used today. They're general purpose, equally adept at calculating inventory or handling airlines reservations. As mentioned earlier, the digital computers in 1968 were giant, power-hungry beasts, difficult to program and difficult to interface with things like a zoom lens. But maybe there was another way.

The other type of computer is called an analog computer, very popular in the early days of computing, but little known today. The main use of this type of computer is to generate mathematical functions and curves that express mathematical formulas. The earliest analog computers used gears and other mechanical elements. Later models used sophisticated electronic components. While digital computers expressed their output in discrete steps, the analog computer produces its output as a smooth, continuous line or curve with no breaks or jumps.

Another breakthrough. Another piece of the puzzle falls into place.

Just what I was looking for to calculate the path for the zoom lens to follow. What the zoom lens computer would compute, in terms of calculus, was "the integral of the speed of the lens, between the start and stop point, with respect to time."

In other words, given the start and end points, and told how long it should take to get between them, the computer would figure out the correct position for the zoom lens at every point in time during the length of the zoom. Triggering the computer would begin the zoom, directing its path at every point along the way, all the way to the end. All that remained was to design and build the computer.

Easier said than done. While generating the functions required by the zoom lens were theoretically possible, it took months of design, experimenting, and tweaking to get the precision that this task required. The final result is the miniature computer shown at the top of the page.
printed circuit #2- - Doing the impossible - Part 3 - The solutions -  - The Godfather - computer controlled zoom lens - - Tony Karp, design, art, photography, techno-impressionist, techno-impressionism, aerial photography , drone , drones , dji , mavic pro , video , 3D printing - Books -
This is the motor control circuit board. Power transistors, more operational amplifiers, and assorted components combine to give an ordinary DC servomotor an infinite speed range.
Controlling the motor - The next insoluble problem was how to give the motor in the zoom control an infinite speed range. This would be necessary if a director wanted to do a zoom that lasted for minutes instead of just a few seconds. Motors that had enough torque to drive the lens had very limited speed ranges and that's what you found in the zoom controls that were available at the time. But I needed to use the same sort of motor in order to get enough torque to drive the lens.

It was quite a puzzle, so I did a lot of reading and watched the world around me for something that would yield a clue. The first hint that I got was from an obscure manuscript on servomechanisms, buried in a discussion of control systems for radio telescopes. The next clue came to me as I was watching how the machinist, building some of the parts for the system, accurately positioned a vise on the table of his drill press.

From there, it was a matter of figuring how to implement this idea in the system I was building. This one involved the use of an oscilloscope to tune the system until the desired result was achieved. The final result was a control system for DC servomotors that had no low-speed limit. The longest and slowest zooms were now possible. This is what made it possible to shoot the opening scene of The Godfather.

Working with the lens - Some modern zoom lenses come with a gear already mounted to the lens and that makes it easy to attach a motor to drive the zoom. The lens I was working with was meant to be turned by hand and that was it. So the first thing I needed was a way to put a gear on this lens so that I could couple the motor and the position sensor to it.

I searched the catalogs of precision gears and located a gear about half an inch bigger in diameter than the collar around the lens that I would attach it to. I had the machinist cut a hole through the center of the gear just slightly larger than the lens's collar. The gear was then split at one point and a screw went through at this point. The gear could be slipped over the lens's collar and the screw tightened to hold it firmly in place.

The motor and position sensor were both attached to this gear with gears of their own. The position sensor needed something called an anti-backlash gear that removed any play between the two gears for the highest accuracy.

Although the zoom collar on the lens turned easily, the grease in the lens had high viscosity, making it hard to turn at faster zooms. I took the lens to Marty Forscher of Professional Camera repair and he replaced the original grease with a thin silicone lubricant which allowed the lens to turn more easily. It had the additional benefit of maintaining this low torque requirement in cold weather that you would find in outdoor shooting.

This is the level of detail that you have to get into when you take a systems approach to design. Every part of the system has to be considered as a separate element and as part of the whole.

Packaging the system - The final zoom control had three main units.

First, there was the zoom lens itself, with its attached motor inside a soundproof enclosure.

Then, the motor control circuitry and the batteries were in a welded aluminum case occupying less than a cubic foot of space.

The most important piece was the handheld control unit that was used to program and control the operation of the zoom lens. This unit also held the analog computer described above. The control unit was built into a T-shaped handle that made it easy to grip. The main interface was a set of knobs and switches that made it easy to describe the required zoom. A set of four pushbuttons controlled the starting, stopping, pausing, and resetting of the zoom.

The three units were connected together with a set of cables, Each connector had a different number of pins, making it impossible to hook the system together incorrectly.

The interface - My motto is, "Build complex toys and simple tools." The zoom control would be useless if its interface was too complex and difficult to use. I needed an interface that could be used by anyone, after just a brief instruction. In addition the interface should be designed to mirror the way that the person using it understood their job. Its controls should exactly emulate the way that a director or cinematographer would think when setting up a zoom.

The best thing versus the right thing - This is a philosophical issue that helps to guide understanding and choices. For instance, the "best" computer was obviously some giant digital system that would provide a more general solution to this or any other problem. It's a seductive trap that many designers fall into. The solutions listed above were, in part, made possible by rejecting this sort of thinking.

Revolution versus evolution - Although there were breakthroughs that helped to set the path, the actual process, from beginning to end, was a set of tiny steps, at each point focused on improvements, tweaks, and tunings that would yield a small additional benefit. Every day, the system and its component parts were examined again as if for the first time, with an open mind, ready for some new insight. This examination never stopped during the years that it took from the very first steps to the finished design. And even today, I still think about the design and what sort of improvements remain to be made.

Once you understand this sort of Zen approach to solving problems, you will be like the butcher whose knife never got dull.

Part 4 will show what the finished system looked like.
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