International projectionist (Jan 1963-June 1965)

POWER SWITCH \ IMAGER SCREEN AUXILIARY REfLECTOR ADJUSTMENTS FIG. 4 — Convenient arrangement of the simple controls of the Strong K.-16 xenon lamp. The accompanying text explains the use of these controls. several layers of canvas or hem y cloth and smashed with a hammer before being deposited in the trash can. Simple Servicing, Cleaning Never open the lamphouse u licit the xenon hull) is in operation! U ait at least ten minutes for the bulb to cool before opening the door. The purpose >>t 1 1 1 i — precaution is to prevent cracking ami explosive destruction of the bulb from the chilling effects of drafts. For tin same reason, the ventilating system must be arranged so that down-drafts cannot force their \\a\ into the lamphouse. The ventilating requirements of the xenon lamp are modest, inasmuch as the xenon bulb, unlike a carbon arc. generates no gases to be expelled. Once a xenon lamp has been connected to a suitable rectifier, power-suppl) problem seldom arise. There are no electro-mechanical feed mechanisms to go wrong. The quench spark gap of the high-voltage igniter unit maj need adjustment or replacement after long periods of use, but there are no moving parts in the xenon lamp aside from the expected mirror-adjusting controls. No lubrication of the lamp is needed. There are no carbon-core ashes to soil the lamphouse. hence cleaning is an exceptional eas) chore. The large main reflector and the small auxiliary mirror ordinarily require no cleaning beyond a fortnightly wiping with a clean, soft, dry cloth. Adjustment of Mirrors Detailed instructions for "lining up" 900-, 160U-. and | 2500-watt xenon lamps are given in the Strong operating manuals for these lamps. Initial alignment of the xenon lamphouse is best accomplished with the aid of a special aligning tool supplied by the lamp manufacturer. The three control knobs for the main reflector are | located on the operating side of the lamphouse at the ' rear: the three for the auxiliary reflector are at the front of the lamphouse. So critical is the adjustment of the auxiliary mirror that its controls should be locked in place once the adjustment has been made. The large main reflector is adjusted first. To prevent the appearance of confusing patterns of light on the screen, the optical effect of the auxiliary mirror is eliminated bv mo\ ing this smaller mirror toward the front of the lamphouse. The xenon bulb is switched on and the light centered on the screen with the main-mirror horizontal and vertical adjusting knobs, then focused with the focus knob to obtain the smallest "V" pattern of light. After this is done, the auxiliary mirror is returned to its normal position, and its optical adjustment effected bv means of the horizontal, vertical, and focus knobs for this mirror, as described below. Optical adjustment of the auxiliar) mirror is very critical and must be performed with great care. The horizontal and vertical controls are adjusted until the bright "cathode spots" are aligned vertically, one above the other, on the imager screen in the side door of the lamphouse. The two bright spots should be about 1/8 inch apart on this little screen, and care should be taken not to focus the bright spot of the cathode directly upon the tip of the anode. To do so will overheat the anode and harm the xenon bulb. This done, further adjustments ol the auxiliary mirror are made bv observing the projected light on the theatre screen. After giving a finishing touch to the auxiliarymirror horizontal adjustment, if nccessarv. the auxiliarymirror focus knob is adjusted to obtain the brightest paltern of light on the screen. This will be superimposed upon the "V" pattern formed bv the main reflector. To "disentangle" the two patterns, it is advisable to run through the focal position of the auxiliar) mirror a lew limes before a fine adjustment is made. \lter these patterns of light from the main and auxiliary reflectors are obtained, the last step in the adjustment of the reflectors is to turn the auxiliary-reflector focus knob one-half turn to the right, and the mainreflector focus knob two turns to the right — that is to say. in a clockwise direction. This will then provide a screen light of utmost uniformity, and all is in readiness for the projection of pictures. Pushbutton Starting \etual operation of the xenon lamp is simplicitv itself. There are two switches directlv beneath the three mainreflector adjusting knobs. One is the rectifier-relay ON — OKI switch for the power. This is turned on first. Then the igniter button is pressed [or not more than half a second. There will be a distinct buzzing sound, and the xenon bulb will light up. What could be easier? Because of the slow evaporation of tungsten from the hot electrodes, the quartz envelope of a xenon bulb gradually darkens — just the same as with an ordinary tungstenfilament mazda lamp. To maintain a constant high light output, therefore, the current is graduallv increased by small increments at the rectifier. When the current has been boosted to a stated maximal value, after many months or even a year or so of service, the bulb must be replaced. Too high a current destroys the tip of the tungsten cathode and dangerously increases the pressure of the gas inside the bulb. Xenon lamp equipments manufactured by the Strong Electric Corp. have a running-time meter which shows the time in hours that the xenon bulb has been burned. The running-time meter is conveniently located on the back of the lamphouse beside an ammeter which shows at what current the lamp is operating. Imbalance in the light outputs of xenon-equipped projectors is corrected by increasing the current of the dimmer lamp, decreasing the current of the brighter lamp, or by a combination of both measures. All things considered, the xenon lamp is a welcome boon to projection in theatres which formerly found the smaller simplified high-intensity carbon arcs adequate for satisfactory screen brightness. It is designed to produce an ideal light for motion-picture projection and to provide long periods of service with an absolute minimum of attention. iP International Projectionist July, 1963 17