Transactions of the Society of Motion Picture Engineers (1922)

The Illumination with Small and Large Condensers By W. E. Story, Jr. THE present paper is the outgrowth of the discussion in connection with the paper on condensers at the last meeting of this society. The method previously described has been applied to measuring the efficacy of small condensers as compared with the standard 4.5 inch, for sources and projection lenses of a variety of sizes. A graph showing the relation between brilliancy of incandescent filaments and lamp life has been added. The apparatus used was essentially that previously described in these transactions (^), except that the use of a more sensitive cell permitted the return {^) to an opal glass (O, Fig. 1), instead of a condenser beyond the dummy projection lens (P). The cell (C) was placed 6 inches from O and the inside of the cell box painted w^hite to insure a deflection depending on the quantity of light falling upon the opal glass, and not on the particular part of it illuminated. This substitution allows of a simpler unit of deflection, as will appear later. Fig. 1 — Diagram Showing Arrangement of Apparatus Used in the Investigation. As before 5.5 inches was selected as the distance (dg) between the Standard aperture plate (A) and projection lens opening (P). The openings used were 2.5 inches, 2 inches and 1.5 inches. In the case of the Safety Standard aperture, dg was chosen as 3.75 inches and openings of 2 inches, 1.75 inches, 1.5 inches, 1.25 inches and 1 inch were employed. As before, these openings were simply holes cut in thin brass plates, and accordingly all the measurements of illumination, referring as they do to that light passing thru these holes, must be interpreted as light delivered to the projection lens. Accordingly, to find the light on the screen, these values must in each 19