British Kinematography (1950)

168 BRITISH KINEMATOGRAPHY Vol. 17, No. 5 Securing Arc Lamp. The arc lamp is secured to a large hinge along its rear edge by a single bolt in a slotted hole. A large screw under the front of the lamp tips it up and down to give vertical adjustment of the crater ; two screws at the sides of the front of the lamp swing it across for cross adjustment ; and for longitudinal adjustment the whole lamp is moved bodily. Although the lamp weighs 300 lbs. these adjustments are easily made and are readily locked off. The three movements on the slide holder are based on the typewriter carriage principle ; the slide is held accurately square to the optical axis with the minimum of " wobble," and yet may be easily moved by the M-motors. Controls and Adjustments. All the controls of these adjustments (and the main tilt control) are fitted with stops which act when the end of the movement has been reached. These operate as near as possible to the hand-wheels, so that none of the internal mechanisms are accidentally damaged ; this reduces servicing troubles. The direction of movement of the picture resulting from turning any control has been standardised according to the convention that clockwise rotation moves the picture to the right, or downwards. In the remote control desk the electrical connections to the cross-movements have been reversed, since the operator there is looking at the other side of the screen. The controls are labelled and their direction of movement shown by arrows. They are all on one side of the machine, and all electric cables and other pipes couple into the other side with quick-release connectors. The electrical connections between various units are made with colour-coded plugs and sockets, so that no wires have to be undone to remove any part should trouble occur. The minimum number of different sizes of bolts have been used to reduce the number of spanners needed for servicing. All screws have coin-slots for quick removal in emergency, particularly on covers to electrical gear. Facilities for Double and Triple-Head Work. For very large shots or when extra brightness is required, two or three of these projectors may be placed side by side with identical slides in each. The total light output, and, therefore, the total area of the picture is accordingly doubled or trebled. To ensure that exact overlap of the pictures is obtained, without any keystone distortion of the picture from the outer projectors, it is necessary that the slides in their holders are exactly parallel to each other, and then the crossmovements of the objective lenses are operated until the pictures merge. Superimposing Screen Images. Two methods are available for aligning the slides. Using the first, the projector is fitted with a spirit-level in a holder which may be inclined. The holders on the projectors are set at the same figure (in degrees) and the main tilt controls operated until the bubbles are in the centre of the glasses. For alignment in the other directions two V-notches are accurately mounted above the slide-holder ; spare carbons may be placed in these, and the pan controls turned until the carbons are sighted in line. After this, the main pan and tilt controls should not be altered, but the pictures merged by the adjustments on the lenses. The second method is optical. Due to the wide range of movements available on the lens and slide, big errors could be introduced if they were in the wrong position. Accordingly, all these controls are first set to their centre, on-axis, positions, which are shown for each adjustment by an indicator and graduated scale. The two (or three) pictures are then thrown on the screen, and the main pan and tilt controls turned until they are on the same level but displaced about 4 feet apart sideways, this being the distance between the objective lenses