How to Make This Valuable Aid in Landscape Drawing.

To those who find pleasure in landscape drawing, but, from lack of a teacher, cannot master the elementary principles, the camera obscura here described will prove of much assistance. It is easy to make and use, and requires but little expense for the materials used in its construction.

The view is thrown by the lens on the mirror, then to the ground glass, and there appears reduced in correct proportion. It is made permanent with pencil or crayon. The practice in drawing thus obtained is valuable to beginners.

The required materials are: a wooden box, a cheap double-convex lens, a piece of mirror and one or more pieces of ground glass, a piece of pasteboard mailing tube, some dull black paint or paper, sheet tin, screws, etc. The first thing to be settled is the lens. The one used by the writer was a discarded photographic lens from a cheap 5" x 8" camera that had outlived its usefulness. Any jeweler can supply an ordinary double-convex lens at a small price. One that is 1" diameter is large enough, though 11/2" would be better. The depth of focus should be as short as possible, and this measurement should be learned when purchasing, as the length of the box depends upon it.

Having secured the lens, get a well-made and smooth piece of mailing tube about 3" long, the inside diameter of which is a little larger than the lens. From the jeweler also get a case such as the works of watches are shipped in. The cap of this case will make a good frame for the lens. Mount the lens in the cap, which should fit snugly into the mailing tube. If such a cap cannot be obtained, two pieces of brass wire about \" diameter bent into circles and put into the tube, one on each side of the lens, will keep the latter securely in place. Before fitting the lens to the tube, the latter should be coated with the black paint or paper to prevent cross reflections of the light which enters the tube.

Cover some thick cardboard with the black paint or paper, then cut out a diaphragm, D, with an aperture of about 1/2", though it is desirable to have several, with apertures of different sizes. They should be a snug fit to the tube, so as to remain in position. The tube is now ready to be fitted to the box.

The box here described was made for a lens with a 10" focus, and to give a view on the ground glass measuring 6" x 8". The dimensions are easily determined for any other size of lens or ground glass. The box was remade from a pine box secured from a grocer. It measures outside 131/2|" long, 81/2" wide and 5/12" deep ; the ends being 1/2" thick and the sides, top and bottom 1/4" thick.

A few extra pieces of 1/4" stock are needed for supports. The top piece does not cover the whole top, but only 7" of the front or lens end. The inside of the box is coated with the black paper or paint, to prevent absorption of the light rays entering through the lens.

A hole is bored in the front end to receive the lens tube. This should be of such a size as to hold the tube firmly and yet allow it to be drawn out or pushed in for focusing. A good plan is to have this hole large enough to allow a lining of black felt. The tube can then be readily adjusted, and yet no light can leak through around the edges.

The mirror M is placed in the back of the box at an angle of 45 degrees and supported on triangular pieces of wood, C, 1/4" thick, and also by a thin beveled cleat, N, glued to the bottom of the box. Two pieces, P, 1/4" wide, 1/4" thick and 6" long are screwed to the sides for supporting the ground glass, and are so placed that the glass is even with the top sides of the box at the rear end.

The ground glass should be of medium thickness, to safely support the weight and pressure of the hand while drawing the view. Extra pieces may be provided so that several views may be drawn during a day's outing and carried home to transfer to paper. The glass is held in position by strips of wood, V, 1/4" thick and 1/2" wide, on the sides and back. These are fastened by screws or screw-eyes.

The hood II is made of tin painted black on the underside and any color desired on the top. A piece 131/2" long and 11" wide is required. The shape of the sides is shown in the drawing. These are cut out with metal shears and the ends bent over as shown. At J a screw-eye holds the side in place while the back part rests on the round-headed screws E, one on each side, which project sufficiently for this purpose. When not being used, the screw-eye J is removed, the front of the hood moved forward so that the screw-eye may be put in the hole K, thus allowing the hood to be laid flat on the top and protect the ground glass from being broken.

The instrument is now nearly complete. It should be tried by taking it out in the sunlight and focusing on a suitable view. Examine the ground glass to see if the view is correctly and squarely reflected thereon. It may be found desirable to put in a shield, S, made of a piece of wood or pasteboard painted black and of sufficient width to prevent the direct rays which enter the lens from reaching the ground glass other than by reflection from the mirror.

In use it will be necessary to place the camera obscura upon a tripod, camp-stool, or other firm support, as some little time is usually required to draw a landscape and any movement would be troublesome. If the sun should shine, a black umbrella will be useful for a shield, as the less outside light that reaches the ground glass, the more distinct will be the definition. A pencil or crayon, black or colored, may be used for the drawing, doing the upper part of the view first to avoid rubbing.