International projectionist (Jan-Dec 1958)

cuits, Associated British Cinemas, that most such complaints relate to poor locus. Very seldom are complaints made of poor screen illumination or sound. Undoubtedly an important factor is the use of old lenses which are not capable of the results expected today, particularly in regard to the coverage of the large CinemaScope frame. Misting of the glasses was stated to be due to the lens "breathing" in the greater heat caused by a more powerful arc and color films, and so sucking in dirt and dust from the atmosphere. Leu Rider, of Twentieth Century-Fox, mentioned that he had noticed an image of the mirror frame and front positive jaw imprinted in the bloom, he believed caused by an electrostatic effect. Mechanical faults such as the gate not being perpendicular with the optical axis, and gate skates not flat, are also causes of uneven focus. On the other hand, he was of the opinion that the curved screen might even improve focus, because the lens rarely has a perfectly flat field. Mass-Producing Optical Glass In Hollywood's studios, many of the camera lenses are, we are told, made by the English firm of Taylor, Taylor & Hobson, Ltd. Their quality owes much to the high grades of glass used in their manufacture, most of which is made by the old-established firm of Chance Bros., who a century ago supplied glass to the German lens makers. Until recently optical glass was made in the traditional manner: the ingredients were melted in a clay pot, and after cooling and annealing the pot was broken up, and suitable chunks of glass were selected for re-melting, moulding, grinding and polishing. But glass blanks for lenses are now being made by mass production. At St. Asaph, in North Wales — the uppermost of the three prongs that on the map stick out to the left-hand side of England — the firm of Chance-Pilkington has built a 21/2-rnillion-dollar ultramodern factory in which the ingredients are put in at one end of the machine, and the finished mouldings come out at the other. The output of the factory will shortly be 60 million blanks a year. The new plant operates under license from the Corning Glass Works and under the agreement we were not permitted to see all of it. But we saw enough to realize the brilliant way in which the many problems have been overcome. First, the special sand is mixed in a roller mill with various chemicals, according to the type of glass needed. The "frit," as it is now called, is transported to the furnaces, where it is melted into glass. Obviously a major factor in the success of the process is the exceedingly close control of this operation. Although we were not permitted to see the furnaces, we saw the control rooms where were dozens of meters recording and maintaining the temperature at various points. The temperatures indicated ranged from 1210°C to 1570°C. From the furnaces the molten glass passes down a chute to the moulding machine. This consists of a number of gas-heated moulds on a rotating table; as the mould moves underneath the chute, shears cut off a "gob" of glass, which drops into the mould, where it is pressed into shape and allowed to cool. To ensure the gob being of correct weight, a control of temperature to within 2°C is necessary. When the moulding has cooled slightly, it is picked up by a vacuum suction, and dropped on to a belt which carries it into a lehr, or continuous annealing oven. From the other end emerge the glass mouldings ready for despatch to opticians throughout the world, for making into lenses of all sorts. Projectionist License Exam Questions THIS DEPARTMENT has been running for some time now, and surprisingly, we haven't run out of questions. Which only goes to prove that the projectionist's job is not exactly uncomplicated. On the official exam, 75 per cent is passing. You should do better, and to make sure you will find correct (we hope) answers on page 19. 1. The AWG (American Wire gauge) wire table gives copper wire sizes in: (a) square mils; (b) square inches; (c) circular millimeters; (d) circular mils; (e) circular inches. 2. Copper wire is measured by the: (a) diameter over insulation; (b) cross-sectional area of the insulation; (c) cross-sectional area of the copper; (d) type of braid on the wire; (e) type of insulation used. 3. An economizer is a: (a) variable rheostat; (b) step down transformer; (c) circuit protector; (d) convenient means for reducing light; (e) a discount on electrical equipment. 4. Designate by letter the piece of electrical apparatus that doesn't belong with the group: (a) generator; (b) transformer; (c) (c) copper oxide discs; (d) transverter; (e) tungar bulb. 5. An Edison 3-wire system provides: fa) fluorescent lighting; (b) a raw DC source of power; (c) a raw AC source of power; (d) auxiliary current for the amplifier; (e) a special line for operating AC motors. 6. A transformer that raises the voltage above the level of the input voltage is a: (a) step-by-step transformer; (b) step-out transformer; (c) step-down transformer; (d) step-off transformer; (e) step-up transformer. 7. An optical train consists of: (a) arc and aperture; (b) projected light and screen; (c) a series of lenses; (d) a ground glass mirror; (e) a metallic mirror. 8. When a ray of light strikes a polished surface obliquely, the angle of the reflected ray is equal to the: (a) angle of refraction; (b) refractive index of the surface; (c) critical angle; (d) angular motion; (e) angle of incidence. 9. Refraction of a light beam occurs when a ray of light: (a) strikes a reflecting surface at an angle (b) is interrupted by a sound wave; (c) is absorbed by a translucent medium; (d) passes at an angle from one medium to a medium of different density; (e) strikes a metal surface. 10. Glass mirror reflectors in lamp houses are capable of intercepting light beams over an area of: (a) 70°; (b) 90°; (c) 100°; (d) 120°; (e) 180°. 11. The image formed by motion picture projection is: (a) a virtual image; (b) an imaginary image; (c) a real image; (d) a demagnified image (e) a reproduction of an image formed at the condenser lens. 12. Lens are effectively cleaned with: (a) soft cloth, grain alcohol and water; (b) soft cloth, denatured alcohol and water; (c) hard cloth, grain alcohol and water; (d) hard cloth, denatured alcohol and water; (e) an acetone solution 10 INTERNATIONAL PROJECTIONIST JANUARY 1958