Modern magic lanterns; a guide to the ... - Yesterday Image

76 MODBEN MAGIC LANTEEN8.is,if the screen has the position indicated by one or other ofthe dotted lines, the pictures thrown upon it will be distorted.It will he seen from this that if the lantern is tippedup or down the screen must not be vertical. The same remarksapply with equal force to the turning of the lanternto one side or the other.Having seen about this, the lantern can be lit up, when,if limelight is to be used, the light will have to be centred,that is, adjusted until the brightest part of the lime is inthe axis of the lantern, and is also, at the focus of thecondenser. (Oil lamps are not provided with a means ofcentering the light, as its position is invariable, and is or•-. Fig. 69. Photographs op the Screen withTHE JET In and Out op Position.should be adjusted by the maker.) To do this, the jet havingbeen lit and the oxygen turned on, a slide must be put intothe lantern, and disregarding for the moment whether itsillumination is even or not, focussed upon the screen, afterwhich it can be taken out without disturbing the focussing.The chances are that the circle of light upon the sheet willnow resemble either a, b, c, d, or e, Fig. 59, which indicaterespectively that the light is too high (a), too low (b), toomuch to the right (o), or to the left (d). This must be correctedby slackening the screw which holds the jet in positionon the tray pin, and finally clamping it again when the discpresents the appearance denoted by e. When this is the