American cinematographer (Jan-Dec 1940)

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Practical Amateur to Begiiijiers: Lens Equipmeiiit Characteristics By JAMES A. SHERLOCK, Vice President Australian Amateur Cine Society PART I THIS is not a story of the Laws of Optics or the production of cine lenses, but rather an attempt by a practical amateur cinesmith to explain to beginners and other amateurs who are striving for better pictorial quality in home movies why they won't go far if they don't know the characteristics and limitations of their lens equipment. The cine lens is an exquisitely de 1 1 f/'\9 25 m m lens ^/3 5 2 IN signed precision instrument which has made practical home movies possible, and is the most important single part of a cine camera. Therefore, it should be of the highest quality in design and workmanship. Its price is not as good a guide to its quality as the well-known names of several manufacturers who produce cine lenses capable of recording brilliant theatre-quality pictures having 1/^7 15mm lens (WIDE-ANGLE) LENS sharp definition and a flat field extending over the full surface of the picture. These people have a world-wide reputation, and even their sometimes undervalued f.3.5 fixed focus lenses are of all round excellence, and owing to the simple operation of these len.ses they can be thoroughly recommended to beginners. Cine photographic objectives are never made of a single piece of glass. They require a combination of several different types of glasses all ground to special shapes and sizes. High class cine lenses cannot be produced cheaply due to the incredible accuracy required in their design and manufacture. It is essential that the amateur realize this fact before money is wasted on cheap inferior lenses which to the uninitiated are similar in appearance to the modem precision made cine lens that has reached such a remarkably high standard of perfection. Years of research by optical scientists have resulted in them reaching the pinnacle of accuracy humanly possible when they produce a cine lens containing several separate glasses each ground and polished to an accuracy of half a millionth of an inch. Herewith are diagrams showing elements of several Cine Kodak lenses which are made from the finest optical glass of exceptional transparency. The exact curvature for these elements, the refractive index and thickness of each glass, together with the exact air space between each element, has to be calculated to an infinitesimal tolerance by lens designers before their computations can be executed in metal and vaious types of glass. Cine lenses are classified by three factors: focal length, speed rating and lens mount. FOCAL LENGTH Technically the focal length of a lens is the distance from the optical centre :X: of a lens to the film, but is generally accepted as the distance from the centre of the lens to the film. Actually it defines the boundary and perspective of a scene. *Technically, the optical centre of a lens is the point where light rays converge and pass through the glass without being bent or affected. Most cine cameras are so designed that lenses of various focal lengths are interchangeable, while the best designed camera for serious workers is one with a turret holding several lenses that can be interchanged in a fraction of a second, but, of course, this extra equipment adds to the cost and weight of a camera. Since the ratio of focal length to size of film is about the same in each case, the results of a half-inch lens on 8mm. cameras is comparable with a one-inch lens on a 16mm. camera or a two-inch lens on a 35mm. professional camera. All these lenses are recognized as standard and give more pleasing perspective :X: than normal lenses supplied vnth still cameras. Scenes photographed (Continued to Page 272) */21 2-5 IN. LENS f/2 7 4 IN. LENS 16 MM CINE-KODAK LENS TYPES 260 June, 1940 AmĀ£1rican Cinematographer