. Transactions of the Society of Motion Picture Engineers (1921) . sers By W. E. Story, Jr. THE present paper is the outgrowth of the discussion in connec-tion with the paper on condensers at the last meeting of thissociety. The method previously described has been applied to meas-uring the efficacy of small condensers as compared with the inch, for sources and projection lenses of a variety of sizes. Agraph showing the relation between brilliancy of incandescent fila-ments and lamp life has been added. The apparatus used was essentially that previously describedin these transactio
. Transactions of the Society of Motion Picture Engineers (1921) . sers By W. E. Story, Jr. THE present paper is the outgrowth of the discussion in connec-tion with the paper on condensers at the last meeting of thissociety. The method previously described has been applied to meas-uring the efficacy of small condensers as compared with the inch, for sources and projection lenses of a variety of sizes. Agraph showing the relation between brilliancy of incandescent fila-ments and lamp life has been added. The apparatus used was essentially that previously describedin these transactions (^), except that the use of a more sensitivecell permitted the return {^) to an opal glass (O, Fig. 1), insteadof a condenser beyond the dummy projection lens (P). The cell(C) was placed 6 inches from O and the inside of the cell boxpainted w^hite to insure a deflection depending on the quantity oflight falling upon the opal glass, and not on the particular part of itilluminated. This substitution allows of a simpler unit of deflec-tion, as will appear Fig. 1—Diagram Showing Arrangement of Apparatus Used in the Investigation. As before inches was selected as the distance (dg) betweenthe Standard aperture plate (A) and projection lens opening (P).The openings used were inches, 2 inches and inches. Inthe case of the Safety Standard aperture, dg was chosen as and openings of 2 inches, inches, inches, inchesand 1 inch were employed. As before, these openings were simplyholes cut in thin brass plates, and accordingly all the measurementsof illumination, referring as they do to that light passing thru theseholes, must be interpreted as light delivered to the projection , to find the light on the screen, these values must in each 19 case be multiplied by the efBciency of the projecticn lens used—that is by the prcportion of the light it brings to a focus, to that fall-ing upon it from the aperture. Three small condens
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