The international photographer (Jan-Dec 1939)

(1) PART I THE BASE CONSTRUCTION (Basic) The base shall be so designed that it provides: (1) A rock-like stability during operation, when locked off, and facilities for panning and tilting with absolute smoothness and precision; and (2), sufficient portability so that the whole equipment may be easily moved about on its special carrier or dolly on the recording stage by not more than two men. CONSTRUCTION (Auxiliary): It has been suggested that this portability be accomplished by the use of a special carrier or dolly of the four-wheel type (on which the base will be mounted), equipped with solid rubber tires to insure safety and stability during movement of the equipment. The wheels should have the ability, free from any side play or sway, to swivel and lock off in any direction for possible dolly shots. To increase stability, suitable jacks should be provided to lift the equipment off the wheels for stationary shots. Adequate bubble levels should be provided for leveling up the equipment. (2i PAN AND TILT MECHANISM (Basic) In the design of the base, provision shall be made for a free-moving and easily operated tilt and pan mechanism, giving a smooth movement when in operation, but including a positive locking device, giving locked-off stability equal to the stability obtained were this pan and tilt mechanism not i provided. There should be no backlash or 'play whatsoever in the pan and tilt meehan!ism and means for adjustment should be provided to keep all working parts tight at all limes. (See "Rotation of the Projector Head," page 18.) PAN AND TILT MECHANISM (Accessory): The design of the base should also provide for the addition, when required, of a variable speed motor control of the pan and tilt mechanism, operating remotely from the camera position. The design of this remote control mechanism should provide for a gear ratio in the order of 900 to 1 between the drive motor speed and the speed of operation of the tilt and pan mechanism (to minimize over-control) as well as a gear box providing ttvo lower gear ratios, making available all the necessary different speeds of operation. PAN AND TILT MECHANISM (Accessory) MINIMUM DEGREE PAN AND TILT (Basic) The base shall be designed to provide an angle of pan of at least 15° to both right and left of the center line between the projector and the screen, making a total minimum horizontal coverage of 30° and to provide an angle of tilt of at least 10° above and below the horizon, making a total minimum vertical coverage of 20°. INTERCHANGEABILITY (Basic) The base shall be so designed as to allow for free, quick interchange of projection heads and lamphouses, registered with dowel pins or other positive means so that a minimum of adjustment is required for lining up when a change in head or lamphouse is made. INTERCHANGEABILITY ( Accessory ) : In the event that devices other than the regular base mentioned above are provided to hold , the projection head and lamphouse, the base on j which the projection head and lamphouse rests should be designed so that projection heads and lamphouse are easily and quickly interchange! able to such devices. ! SOUND INSULATION (Basic) The base shall include sound insulation [ to eliminate the transmission of noise. (It has been observed that sufficient sound insulation has been provided by insulating the setting jacks of the dolly with hard rubber. However, it must be remembered that any material so used must not. in any way, detract from the absolute steadiness of the whole equipment.) (See "Maximum Noise Level," page 21.) (3) HEIGHT OF OPTICAL AXIS (Basic) The base and special carrier shall be so designed that the equipment's optical axis, when parallel to the stage floor, shall be 5' 6" from the stage floor. PART II THE LIGHT SOURCE EFFICIENCY OF THE CARBON LIGHT SOURCE (Basic) The type and size of carbon shall be carefully chosen for maximum efficiency in relation to the selected type of optical system and lamphouse. EFFICIENCY OF THE CARBON LIGHT SOURCE (Auxiliary): It is recommended that all motion picture producing companies and commercial organizations using process projection equipment follow the manufacturers' rated burning conditions under which the maximum efficiency and minimum flutter and flicker are obtained from the carbon light source. (See "Light Control," Page 14.) It is further recommended, to insure freedom from moisture or dampness, that carbons be kept for 48 hours before use in an electric heating oven operating at not to exceed 125 °F. TOLERANCES IN THE STRAIGHTNESS OF CARBONS (Basic) Carbons for process projection shall be so selected by the manufacturer for straightness and concentricity of the core, that when burned in a lamphouse developed and constructed to meet these Recommendations, the equipment shall be able to fulfill the Tolerances under "The Feeding Mechanism," page 9, as well as the recommended "Tolerances in Light Variation of the Light Output," page 4. MAGNETIC SHIELDING (Basic) The current to the arc shall be so conducted into the lamphouse that no magnetic fields disturbing to the arc are set up. (4) INCANDESCENT LIGHT SOURCE (Basic) It is recommended that further development work be conducted on incandescent and hi-pressure mercury vapor lamps for general and special application to background process projection. POWER SUPPLY (Auxiliary): It has been suggested that a separate power supply be provided for the light source, inasmuch as a constant line voltage to the arc is imperative to accomplish the results to be obtained from equipment meeting these recommendations. PART III MAXIMUM VARIATION IN LIGHT OUTPUT OF EQUIPMENT TOLERANCES IN LIGHT VARIATION OF THE LIGHT OUTPUT (Basic) The design of the whole equipment shall be such that the illumination from the carbon arc light source approaches as closely as possible the steadiness of an incandescent source. In any event, the amount of light variation during the projection of a scene shall be less than ±2% per minute but with a maximum of ±5% for any consecutive nine minute shooting period. This tolerance is to apply only after a proper crater has been formed in the arc. DEFINITION OF LIGHT VARIATION (Basic) There are two distinct types of variation in the light output of an arc lamp, which can be designated as "flicker," viz: a sudden sputter or brief increase or decrease in brightness, and as "fluctuation" (flicker may be caused by the core of the positive carbon having different consistency in var ous spots, causing the arc to momentarily sputter, or by sudden air drafts or misdirected magnetic flux, or by misalignment of the negative carbon with respect to the crater. Fluctuation is a mechanical or electrical problem and is caused by off-center rotation of the crater, the carbon feeding in an irregular manner, crooked carbon, or disturbances in the line voltage), viz, moving in a sloiv wave of increasing or decreasing brightness. (5) FLICKER — METHOD OF MEASUREMENT (Basic) Flickers are generally too fast to be measured by any presently known meters, but shall be measured by photographing a clear screen illuminated by the arc lamp source. Each frame of the exposed, developed negative, over given portions, can then be read on a densitometer. (It is recognized that this method of measuring flicker may not be the most accurate, due to variations in film development, but is one simple means available at present. The committee will welcome suggestions on more accurate methods which may be devised.) FLUCTUATION — METHOD OF MEASUREMENT (Basic) Fluctuation can be easily read and recorded with an accurate, sensitive lightrecording photometer. PART IV THE LAMPHOUSE General Recommendations Applying To Both Mirror and Condenser Type Lamphouses CAPACITY AND OPTICAL SPEED (Basic) Recommendations covering capacity and optical speed for each type of lamphouse are given in that Section of this Part of the Report specifically applying to each type of lamphouse. NOISE LEVEL (Basic) The noise level of the lamphouse in operation shall be 8db below the noise level specification given for the whole equipment in that Part ("Noise Level," page 21) of these Recommendations. This specification must be met without the use of booth or blimp on the lamphouse. NOISE LEVEL (Auxiliary): It has been suggested that acoustic treatment of the lamphouse might prove effective in meeting the above basic Noise Level Recommendations. (6) STRIKER MEANS (Basic) The lamphouse shall be provided with a striker, hand or motor, which produces no detrimental magnetic effects on the burning of the arc and which will not shatter the crater. VIEWING PORTS (Basic) Large adequate viewing ports shall be provided in both sides of the lamphouse, located at the most advantageous position. LAMPHOUSE DOORS (Basic) The lamphouse door shall open upward rather than outward (forward or backward) and shall be provided with a positive holding device when open. (It has been suggested that the lamphouse doors be of the type which fold or collapse into a smaller unit when opened.) CONTROL AND METER PANEL (Basic) Controls and meters shall be centrally located at one position on the operating side (the right side facing the screen) for ease of operation of the equipment (exeept for special purposes). OPERATING POSITION (Accessory): The lamphouse should be adaptable to operation from either the right or the left side for special purposes. International Photographer for March, 1939 23