The black twill or the focusing cloth (or even a dark table cloth may be used) must also depend for its size on the length of bamboo, but sufficient should be obtained to completely cover over the space between lens and negative, and hang down on each side. Of course, two laths of wood can be used, merely resting them on the top of printing frame and camera, but the other plan is preferable, the arrangement being more complete and adaptable to both day and artificial light, and also more rigid, especially when the camera is sloped toward the sky. The ordinary camera may be used, but a carrier to take lantern plates must be used in the dark slide. The ordinary lens may be used unless of inordinately long focus, when it becomes inconvenient on account of the great distance between negative and lens. To find the required distance there is a simple rule, which is as follows: (a) Divide the longer base of the plate by the longer base of the image required, to the quotient add 1, and multiply by the focus of lens used; the result will be the distance between negative and lens. (b) Divide the distance found as above by the quotient obtained in the first rule, and the result will be the distance between lens and plate. Example.--What are the relative distances in reducing a whole plate negative, 8½ X 6½ inches, to lantern, size with an 8 inch focus lens? Now that the whole of the lantern plate is not used, we reckon that 3 inches is all that can be used, because of the mask, hence: (a) 8½ ÷ 3 = 17/6 = the amount of reduction. 17/6 + 1 × 8 = 23/6 × 8 = 30-2/3 inches. (b) 30-2/3 ÷ 17/6 = 11 inches (practically). Therefore, if we place our lens about 30 inches from the negative and rack the camera out to about 11 inches, we shall have an image on the ground glass which merely requires a little adjustment of the camera screw to be sharp and of the right size. In focusing, it is always advisable to temporarily affix to the outside of the focusing screen a square mark, this being, of course, accurately placed as regards the center of the screen, and to use a focusing magnifier to obtain critical sharpness. Having satisfactorily arranged our image as regards composition by shifting the camera nearer to or farther from the negative--because it will be obvious that the nearer the lens to the negative, the less of the negative we shall include, and vice versa--we fill our dark slide and are ready for exposure. For daylight work the arrangement of frame and camera should be placed near a window, and if anything but sky is seen opposite the negative, place outside the window a large sheet of white cardboard at an angle of 45°. This will reflect equal skylight through all parts of the negative. Now cover over the space between negative and lens, insert your dark slide, in front of the negative place an opaque card, draw the shutter of the dark slide, and remove the opaque card from negative and expose.