Page:Popular Science Monthly Volume 89.djvu/782

 7G8

��Popular Science Monthly

��Size of Picture on Screen with Lenses

of Different Focuses When Using

Standard Slide

��Focus

� � � � �of Lens

�15 ft.

�20 ft.

�25 ft.

�30 ft.

�5 in.

�9

�12

�15

�18

�7 m.

�6.5

�8.5

�10.5

�12.5

�10 in.

� �5-8

�7-3

�8.8

��The front board, which carries the objective, may be made first. The design is shown in Fig. 4, and the openings and general form should be described by measuring from the center line. The large openings may readily be cut with a fine jeweler's saw, or if the

e

��shown in Fig. 6. These cylinders are made from thin sheet brass accurately cut and shaped h\ means of a tinner's roll. An accommodating tinner will usually be glad to perform such a small ser\'ice without charge. The smaller cylinder should slide easily within the large one. It is then sweat-soldered to the lens-board, care being taken to see that it is exactly centered.

The slide-carrier holder, with the dimensions of its parts, is shown in Figs. 7, 8 and 9. The piece shown in F"ig. 7 is soldered to the larger cylinder, D, Fig. 2 and the smaller ring of brass wire, Fig. 10, is sweated on at the junction.

���Side elevation

���O

��\

��Lamp hood fn do/fed

//nes \

��front elevation

���P/an

��Fig. 2. The objective assembled. The lenses are usually supplied in a mounting, with a flange and knurled adjusting knob, which actuates a rack and pinion arrangement

��builder has a power-drill, lhe\' may be roughly drilled and finished uji to line with a file. The lens-opening will ob- viously have to conform to the diameter of the lens-barrel or its flange, which is made (A sheet brass, Y^ i'l- thick and secured to the board with maciiine screws.

The lens-board is held upright b\ iwo rods of brass. Fig. 5, which slide into brass tubes. Upon these tubes the remainder of the instrument is assembled. The dimensions of the telescoping c>'lin- ders which supjilant the bellows are

��When llu' c\liiider is to be soldered on, the rods and lubes should be in place and the one cylinder telescoped within the other, to insure accurate centering. As the assembled drawing shows. Fig. 2, the U|)right /? is grijiped between the collars Fwliich are forced over the tubes and soldered in pi, ice. The dimensions of the collars are all gi\en in Fig. II. The |)aris of liu' slide-carrier holder are asseml)led by means of screws; and clamjiing-screws in the top piece are arranged to engage the slide-carrier and secure it in ihe proper posilioii.

�� �