The Picture Holder, and hinge it in place. A frame for post cards to slide in should be fastened to the picture holder, as shown in Fig. 346. First nail strips F to board E, then tack strips G to them so their edges project over strips F. A little wooden button (H, Fig. 345) will fasten the holder board shut while each picture is being projected.
The Lens Reverses Pictures in projecting them, and in order to have them projected right-side up on the screen it is necessary to slip them into the holder frame upside down.
Adjustments. After you have built your reflectoscope, you may find it does not throw sharply-defined images upon your projection screen. In that case you must readjust the focus of the lens, the curve of the lamp reflectors, and the distance between the lens and the projection screen, until the best possible results are obtained. Inasmuch as the positions will vary with different lenses, it is impossible for me to give any hard and fast measurements. You will have to determine the distances yourself.
The stronger the light, the brighter the projected image will be; therefore, use the strongest light you can get, and place the lantern not more than five feet away from the screen.
Unless you use an anastigmat lens such as the better grade of cameras are fitted with, you will discover that the corners of pictures are indistinct when you have brought the centers to a sharp focus. This indistinctness can be corrected to a great extent by blocking out the holder to curve the post cards and other pictures so that the ends are closer to the lens than the center is.
