From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Working instructions for the SEI Exposure Photometer for estimating camera exposures.
| Identifier | ExFiles\Box 168a\3\ img521 | |
| Date | 1st May 1950 guessed | |
| SEI Exposure Photometer Fig. 1 KEY TO ILLUSTRATIONS 1. Operating ring 2. Setting ring for shadow or key-tone methods 3. Daylight or artificial light setting 4. Adjustable telescope eyepiece 5. Microammeter for standardising comparison lamp intensity 6. Telescope objective 7. Brightness range selector 8. Exposure time scales 9. Lens aperture scale 10. Film speed scale 11. Push button switch 12. Rheostat control 6 Working instructions for estimating camera exposures Note: The instrument is supplied without a battery. Instructions for making it ready for use are given on page 13 under General Instructions. TO DETERMINE CAMERA EXPOSURES FOR MAKING NEGATIVES IN GENERAL PHOTOGRAPHY.—See Fig. 1 1. Set the speed scale. For ordinary black and white negative-making set the black index mark on the narrow knurled ring (2) opposite the appropriate number on the Speed Scale (10). The meter is graduated in British Standard Logarithmic Exposure Indices. An appropriate allowance must be made for any factor known to reduce the effective film speed; e.g. the use of certain fine grain developers, a shorter develop-ment time than that nominally recommended, stale film, etc. The follow-ing conversion table will enable the appropriate exposure index to be approximately derived from other speed systems:— Speed Conversion Table. The values given are for daylight use and allowance for other light sources must be made in accordance with the film or plate manufacturers' instructions. 16 19 22 25 28 31 34 S.E.I. Exposure Photometer (British Std. Log. Exposure Index*) .. 16 19 22 25 28 31 34 Scheiner Degrees (British and Continental) .. 17 20 23 26 29 32 35 D.I.N./10° .. 7 10 13 16 19 22 25 Approx. H.{Arthur M. Hanbury - Head Complaints} & D.{John DeLooze - Company Secretary} (British) .. 100 200 500 800 1600 3200 6400 Weston (Daylight) .. 2.5 5 10 20 40 80 160 Johnson—“Wellcome” etc. (Column 1) .. 1/4 1/2 1 1 1/2 2 3 4 Ilford Group .. A B C D E F G A.S.A. Speed Number (American Standards Assoc.) .. 3 6 12 25 50 100 200 British Standard Arithmetical Exposure Index .. 3 6 12 25 50 100 200 American Scheiner Degrees .. 12 15 18 21 24 27 30 2. Standardise the lamp intensity. Press the black switch button (11) in the broad knurled ring (1) at the bottom of the instrument. Note the position taken by the pointer of the microammeter (5) at the top. Make the pointer coincide with the standard mark by turning the recessed rheostat control (12), which will be found at the lower end of the barrel of the instrument. Release the switch button after standardising. It should be noted that for ordinary purposes the “standard brightness” setting accuracy need not be too great. A setting above the red mark by one tenth of an inch causes an increased exposure equivalent to about 7 | ||