The international photographer (Jan-Dec 1940)

PROFESSIONAL TypE EXpOSURE METERS Photometer expert presents practical suggestions for design of instrument that, will meet needs of cameramen; features of available models analyzed. Bv SIDNEY ZIPSER This concludes Mr. Zipser's discussion of exposure meters, which nets started with a general review of the instrument in the December. 1939. issue of "'International Photographer." The author has had extensive laboratory and practical experience with photometers and is a member of Local 659. IATSE—Ed Note. In a previous article ice considered the difference between the direct or foot-candle type of meter, which appeared most useful on interiors, and the more popular reflection type of meter which seemed better on exteriors. Now, we will consider features desired in professional instruments of each of these types. Foot-Candle Meters The Weston Model 603. encased in an oak box about nine inches square, has more or less set the standard for foot-candle meters, being accurate, rugged, portable and calibrated in almost any desired group of ranges. However, on actual production, it is somewhat cumbersome and slow, usually requiring a third or fourth assistant who can come running with the magic box when the cameraman whistles and thereafter trot after him as various readings are made, taking care not to tangle the cable running between the cell and the meter in the leading lady's hair or in the actor's soup. Then there is the Weston Model 614 in a black bakelite case which is still a little cumbersome and awkward to use on interiors but which some color photographers like on booster light exteriors when it is calibrated to a triple range of 0-500200-10,000 f.c. The General Electric light meter is the utmost in simplicity and compactness and quite handy to use. However, it should be made available in other ranges, preferably it should incorporate a filter to cut down the high ultra-violet sensitivity, and then possibly be modified along the lines discussed below. A foot-candle meter used for photographic exposure should preferably be pocket sized so that the first cameraman can drape it about his person like a viewing glass as an appropriate and useful decoration. Then it should be flexible so that the meter may be read in various positions, for experience has shown that frequently the cameraman gets down on his hands and knees, or balances himself on one toe, or dangles the thing downward as if he were fishing. In these awkward positions, the cell has to point one way and the meter another. If the cell and the meter face the same direction, or face directly opposite each other in a fixed relationship, both cases are limited in their use. The General Electric light meter having the cell at right angles to the meter calibration is much more useful. Still handier, is the cell mounted in a 360° swivel above the meter such as the writer promoted for the Technicolor cameramen. This particular model used the Weston cell and the General Electric microammeter which were readily adapted to each other. However, either manufacturer should be able to work out a more compact, more efficient and less expensive design as the instrument could be built as a unit. Such a meter should read accurately when tipped at any angle. The cameraman should be able to read the intensity of lights facing him, at right angles to him. and also the intensity of light falling on a wall. The pocket foot-candle meter should have an accuracy of at least plus or minus 10', l.V, preferable I allowing for reasonable temperature variations within a studio. Then means should be provided at the individual studios or a centralized Hollywood laboratory for checking and if necessary recalibrating the instruments against a reputable standard within 24 hours. Ranges should be provided so that the intensity of the key light normally used falls around the middle of the calibration. Figures should be large and easily read in glaring lights. Added ranges using the same divisions of the scale should preferably vary by a factor of 5 (or 10), as a lower ratio makes it easv to confuse the two scales, and usually difficult to divide the scale into simple reading divisions for both ranges. A combination range of 0150-170 or possibly 0-200-100 foot-candles at the present time should take care of both color and black-and-white photography. Means should be provided for calibrating special scales to order: single, double or triple, and the cell and movement should have a reserve sensitivity if convenient lor at extra expense) down to about 30 f.c. full scale in case more sensitivity is desired in a later recalibration. Low ranges will be helpful in process work, altho here the Model 603 Weston is verj practical. There may be some demand for an added scale up to around 10.000 f.c. for exteriors. The multipliers, whether electrical or physical, should be accurate over the full range, and also be fairly accurate to direct and angled light sources up to about 45° or better. Switches or range changers in most cases should be positive locking and labeled in any desired position. Linear responding movements and cells are, I believe, preferable for foot-candle meters. A single range would probably be adequate for most cameramen and the double and triple ranges could be worked out at an added expense. The cell should not be overly sensitive to ultra-violet and blue light as discrepancies in film densities will be noticed between arc and inky lights. If the cell is unstable in infra-red light, as some of them are, a heart absorbing filtering is advisable ( already incorporated in some Weston instruments I . Reflection Photometers Reflection meters furnish a most fertile field for disagreement, as so many designs are possible. Many cameramen are well satisfied with the available models, which have been improved considerably. Others have suggested to me a photometer that could be read directly through the photographing lens or finder; still others have suggested fastening it directly to the camera or blimp with interchangeable lenses to conform to the photographed field. In the first place, what with directors, art directors, set designers, producers, and everybody's assistant looking through the finder, it is difficult enough for the operator to see anything through the camera, let alone the first cameraman. Seriously, though, I believe an exposure meter divorced from the camera is more flexible and practical. You could read exactly the amount of light reflected into the aperture, and still be at sea as far as the correct exposure is concerned. Selective readings of critical portions of the scene are most effective in determining exposure by the reflection method. This (alls for a narrow emergence angle in the meter, so that it embraces a smaller field than the one to two-inch focal length lenses, and can still be read from near the camera position. Changeable lenses and emergence angles would only complicate a relit ct ion photometer and make its use more confusing. I have designed and used reflection meters having an emergence angle of 18 .3