Journal of the Society of Motion Picture Engineers (1930-1949)

2. Optical Characteristics In mapping out this Miltar series, some limitations were imposed on diameters to permit mounting lenses on existing camera turrets. The type of lens was then chosen to provide maximum performance. The 1-in. through 4-in. are 6-element construction of the Speed Panchro or Biotar form, with apertures of //2, or T2.2. The size restrictions limited the 6-in. to//3.5, or T3.7, permitting the use of a well corrected triplet. The 10-in. is limited to //4.5, or T4.9, and is a 4element telephoto of standard form. In each case a special effort was made to use readily available domestic glass. This glass, however, is held to closer than normal commercial index and dispersion tolerances. The performance of all focal lengths is substantially increased over lenses previously supplied and is comparable to the best studio lenses. The aberrations have been corrected to give a crisp, high contrast image over the full frame. The curves showing the aberration corrections are given in Figs. 4, 5, 6, 7, and 8. Part of the information is from the design data, part from actual measurements of production lenses. No attempt is made here to quote resolution values, as the performance requirements of these lenses are based on results in specific cameras. Tests on spectroscopic plates do not give complete information, and tend to give a false appraisal of the practical values because of contrast differences. Vignetting has been reduced on all focal lengths. This has required especially careful balancing of the oblique aberrations to obtain the improved contrast and resolution in the outer portions of the frame. All air-glass surfaces are coated. Cemented elements will withstand the full temperature range and thermal shock requirements of the specifications. 3. Mechanical Characteristics In the styling and general design, care was taken to give the lenses a matched series appearance. The diameters and physical lengths are in steps to correspond with the focal lengths and apertures. Special attention has been given the mounts and glass to obtain rugged con-, struction for meeting thermal shock, temperature range, humidity, vibration and mechanical shock tests. In designing this series to meet the drastic vibration requirements, every part is locked into its respective assembly with special antivibration sealing compounds and deep-set pilot screws, which again are locked into place so securely that they can only be removed by drilling. The lenses are completely operable over the temperature range of — 65 F to +160 F. All tolerances have been computed to offset the size changes for expansion and contraction through the temperature ranges. A special noncorrosive lubricant is used which is not affected by these changes. This lubricant has a vapor pressure so low at 160° that no deposit on the glass is detectable after sustained operation at that temperature. The diaphragm blades are lubricated with an unusual type of material, guaranteeing perfect operation over the full temperature range, with a long operating life. It has the properties of being anti-icing and noncongealing, at extremely low temperatures. Globules of condensed moisture will not freeze to the leaves, and the lubricant itself will not allow any of the leaves to bind together. All metal parts, internal and external, are finished for high corrosion resistance. All aluminum parts are black anodized. Antireflection scoring and a durable optical black are used on all surfaces where required, internally and externally. A high-quality baked synthetic enamel is bonded to exterior Foote and Miesse: Military-Type Lenses 221