Sight-for the Services

Cue (NZERS), Issue 16, 31 January 1945, Page 13

Sight-for the Services

In the past the opinion seemed to be general that German optical equipment was superior to that of the Allies. Since the beginning of the war, British craftsmen have proved that in lens-making they have equalled if not surpassed Germany's best. Hand in hand with this improvement has been the steady progress made in the allied craft of glassmaking. The high' quality of British lenses is making a valuable contribution to the final defeat of Germany and Japan'. Telescopes, range-finders, gun-sights, aerial cameras, tank and submarine periscopes, binoculars, and numerous other equally vital instruments for the Army, Navy; and Air Force are being supplied in everincreasing numbers and of . a steadily improving standard of workmanship. Not only are British firms producing these articles for the whole of the Commonwealth; they are making essential optical instruments for the United States and Russia. .'..Even before the war British glassmakers,. encouraged by the State to carry out intensive research into the making, of optical glass, had reached a standard at least comparable with the es t pre-war German products, raftsmen, whose . ancestors had been making glass for centuries, placed their mow ledge and skill at the disposal of e . research workers,? and a happy en of age-old tradition and modern ecnnique produced the desired results. • difficulties were swept aside, nc u mg that caused by the cutting off supplies of the special sand required , r making lens glass. This was Previously imported from Germany, but as Th* < that Was found to be as good in e J? erman deposits was discovered Kco and a discovery which saved

the industry and enabled it to expand on a scale vast enough to meet wartime' needs. -

Just how important are these allied industries can be gauged from considering two aspects of the warthe Battle of the Atlantic and aerial bombing and reconnaissance. Without the compasses, sextants, telescopes and range-finders made by British optical firms, the Royal Navy could not have defeated the attempts of Hitler’s U-boats to cut the life-line between America and Britain. • -

British camera, lenses which. made possible the taking of aerial photographs showing minute details and detecting Nazi camouflage > paved the way for the effective bombing by the RAF and the American Bth and gth Air Forces. Aerial photography was likewise of great importance in the planning of the D-day landings, and it will continue to play its part in the battles that lie ahead. '■ ■ (

Like few war industries, machinery plays little part in glass-making for optical work. / The ’ craftsman . with his own hands , rules supreme, for in this industry no machine has yet been found to equal the work of man hand. Even the dome-shaped, fire-clay pots, in which the r lens glass is . made, are fashioned by the craftsman without the

/ aid of machinery. In fact, he puddles the clay with his feet, much as the Romans did in centuries gone by. The pots are left to dry gradually for several weeks, until they are ready for their role in life— to provide the houses for the lens glass.

The clay - pots are prepared 'for the main furnace by heating to about 800 ‘degrees Centigrade, a temperature that is reached in gradual stages over a period of, roughly, one week. Then they are transferred to a large furnace in which the .temperature is increased to about 1400 degrees Centigrade before the •’frit” or glass-making ingredient is put into the pot. Once this is done, the furnace is closed up and the process of making glass is really commenced. To make up for the escape of gas from the frit, the pot is topped up. It is then left for approximately 48 hours by which time the glass should have melted and become reasonably free of bubbles. Now the pot is opened and the glass mixture is allowed to cool to about 1000 degrees Centigrade, special apparatus keeping it stirred for five hours of the cooling time.

The pot ■ has all but served its purpose. It is now removed from the furnace and cooled off very gradually over a period of a week, at the end of which . the glass should be ready for processing. The clay is smashed, and the ton of optical glass it contains is broken up into target lumps,' like glittering blocks of ice.

The pieces are sorted, tested for flaws, and graded. Then • they are placed on a slow-moving platform which conveys them through a tunnellike chamber, cold at one end but gradually ; working up to 900 degrees Centigrade at the _ other. At this temperature the glass is soft enough to be pressed into shape, and these shaped pieces are placed in a gas-fired muffle and left to cool for three or four "'days; The process is all but over. The glass is next polished and re-examined for flaws. This polishing takes six hours. After final testing, the glass is either sent out to the instrumentmakers in the form of slabs ready to be sawn into shape, or is moulded by a further heating and. pressing process into the approximate shapes of the lenses or prisms required. In both cases, the glass has to be annealed to guard against internal strain. . Then begins the intricate work of making lenses that are as near perfection as it seems possible to attain.

That British lens-makers are achieving, that high degree of workmanship has been proved by the Services. In postwar trade, it .seems likely that t iey will oust the products of Zeiss and Goertz and establish themselves as the best lens-makers in the world.