Britain Leads In Optical Lens Design

Press, Volume CVIII, Issue 31736, 20 July 1968, Page 5

Britain Leads In Optical Lens Design

<B|/

ROBERT C. COWEN.

natural science editor of the

“Christian Science Monitor”)

LONDON. When it comes to designing fine optical equipment, Britain has quietly become a world leader.

Over the last seven years, scientists at the University of London’s Imperial College have given British industry the design knowhow to turn out advanced lens systems.

At the same time, they have been helping foreign laboratories and observatories solve tough instrumental problems. This includes drawing the blueprints for correction lenses to improve the “vision” of the famed 200-inch telescope on Mount Palomar.

It started in 1960 when Dr C. G. Wynne left industry for Imperial College to see what he could do to take the drudgery out of designing lenses.

Any optical engineer can rough out a lens system fairly quickly. Then comes the battle to make it a good one. He may have to juggle more than 100 different factors to cut the distortions of that system to an acceptable minimum.

Doing these calculations by hand made a burdensome job of even simple lens design. It put many theoretical refinements out of practical reach.

Yet an electronic computer can handle this kind of “dog work” superbly. So Dr Wynne and his new optical design group got the assignment of programming a computer for the job. The Government, through what was then the Department of Scientific and Industrial Research (D.5.1.R.), agreed to put money into the project for seven years. The Ministry of Aviation also helped with funds. It was one of the first Government programmes to nourish the seed of a new technology. A Typical Project A job Dr Wynne did recently for American physicists at the Brookhaven National Laboratory in Upton, Long Island, typifies the success of that programme. At Brookhaven, physicists track interactions of subatomic particles with a device called a bubble chamber. Trails of bubbles in liquid hydrogen mark the passage of the particles. The research demands extensive, highspeed photography to record the tracks.

And this requires a complicated lens system to keep the action everywhere in the chamber within view.

Designing that kind of lens system by hand would have taken an engineer a life time. Dr Wynne went to Brookhaven and did the job in three weeks. Optical laboratories and manufacturers in many countries use computers now. But, thanks to the intensive research Dr Wynne’s group has been able to carry out since 1960, his technique and computer programmes are out in front. That's why several leading observatories have asked him to help with telescope design. ’ Instruments like the 200inch telescope at Mount

Palomar, of Britain’s 98-lnch at Herstmonceux, have distortions that limit their usefulness. For example, an effect called coma stretches out star images so that they look like comet tails. The farther an image is from the centre of the telescope’s field of view, the worse is the distortion. Corrector lenses in front of the telescope mirror can cut down these annoying distortions. They are complicated to design. But, here again, Dr Wynne’s computerised techniques make easy work of it.

Besides the instruments at Mount Palomar and Herstmonceux, he has given design help for the 108-inch telescope of the McDonald Observatory in Texas; the 150-inch being installed at Kitt Peak in Arizona; Canada’s 150-inch Queen Elizabeth II telescope; and another 150inch telescope to be built by an Anglo-Australia project in Australia. Commenting recently on his project’s success, Dr Wynne explained, “When computers came in after the war, it was clear that optical design was a field where they would pay off quite well, although it turned out to be more tricky that we had imagined. “It Made Sense” “I suppose it was this and the general growth of interest in optical design that prompted this department to put the case to the Government for setting up a longterm research project. “I think it has paid off. It made sense, of course. Britain’s optical industry is in moderate-size units, developing big computer programmes involving more money than individual firms wanted to spend on it. “Over the years, we have got a very advanced design effort going here. Industry now uses us freely. We work with firms in different ways. “In getting on with this development work, I’ve been lucky. Opposition to technical work doesn’t arise here as it does at some universities where practical work is considered beneath academic people. “Also, what I’m offering firms is not something speculative. It solves problems they are working on right now.”

And that final point may be the strongest reason of all that Dr Wynne got the support he needed. Commenting on this practical outcome, the Science Research Council, which succeeded D.S.I.R. in research support, observed recently that Dr Wynne’s group “now leads the world in experience in lens design for some types of optical systems.” It seems well pleased with the return on the seven-year research investment.