Mastering a tough business


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I recently had a great day out, visiting a company which is enjoying a massive boom in business, has customers prepared to wait as much as a year for its products, and is trying to recruit dedicated staff to increase output. Yet its chairman says “manufacturing is a tough business to be in”.
In 1892 a remarkable picture was taken, on a 5” x 7” plate, of York Minster. It made use of a remarkable new three-element lens designed by T. Cooke & Sons, which held the focus right out to the edges of the frame. Yet despite this success, T. Cooke & Sons decided they wanted to stay in their core business of telescopes, so sold the lens design to another Leicester company, Taylor Hobson, with the only stipulation that any commercial products kept the Cooke name.
That name is still going strong, thanks to a remarkable devotion to quality which makes touring the factory a thrilling experience, at least if you are sad anorak like me.
Taylor Hobson continued to invest in lenses, particularly for the movie industry. In the silent era you could throw as much light as you wanted onto a scene using carbon arc lamps, but the make a noise which killed them as soon as talkies came in. The Cooke team designed the original Speed Panchro lenses – still revered in some circles – with an aperture of f2 which made them fast enough to use with much less lighting.
As the leader in the British movie industry, in the late 40s the Rank Organisation went on a spending spree, buying up a number of vaguely related businesses, including Taylor Hobson in 1947. Fifty years later Rank decided to focus on bingo and sold the businesses again. Cooke Optics was separated from the conglomerate by a wonderfully enthusiastic and slightly eccentric Californian, Les Zellan, who today is a very visible presence as chairman.
“This was once a movie lens company,” he said. “Now everyone wants to shoot large format digital. That means our market has gone up by orders of magnitude.” Which, you would have thought, was a nice position to be in. Until you look at the complexities of making lenses.
The process starts with mouldings in optical glass, provided by Schott in Germany and Ohara in Japan. These are made to Cooke’s specification, including the frequency response of the material as well as the size and shape. Cooke pays by the weight so getting the mouldings in the rough shape saves money, but even so each piece of glass can cost up to £1000 before any work is done on it.
Inside the factory there is a bizarre mix of high-tech CNC machines and some of the original belt-driven workbenches, using time and cerium dioxide slurry to polish the lenses to a tolerance of 0.01 microns. “Critical elements and tight tolerances are still done by hand,” Les said, adding “even the CNC machines need expert control.”
Once checked for perfection, each element is then coated to minimise light loss through reflections. Competitor multi-element lenses can lose as much as 20% of light through reflection: thanks to the Cooke coating, its lenses lose less than 4%.
But if getting each piece of glass perfect seems like a labour of love, it is nothing when you see the other half of the factory, where they are combined into the finished lens. No-one in the factory talks about “assembling” a lens. It is “fitting”, and the people who do this combine extraordinary skills with remarkable patience.
They are put together, tested, taken apart, adjusted, reassembled, tested again and on and on and on until it meets the tolerances for a Cooke lens. This can take days of work.
This is the bit that made me drop my jaw. It is only at this point that the focus ring is calibrated. No, the focus ring is not a standard manufactured part. It is made plain, and in the calibration stage the precise markings are added, by the fitter, using a large rig which itself it calibrated to millimetre accuracy every morning. Without this ridiculously fine attention to detail the focus puller could not trust the lens to be pin sharp every time, and that is what movie-makers pay for.
Since Les took over the workforce has already doubled, and he will take more if he can only find the right people. It is not a skill you can pick up in a couple of days. As he said, “to make a lens that is optically acceptable and mechanically acceptable to the industry is not trivial.” It was a privilege to see it done: long may it continue.

Tags: iss068 | cooke | lenses | glass | les zellan | optics | N/A
Contributing Author N/A

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