The Boy Mechanic Part 101

** Home-Made Duplicator for Box Cameras [363]

The projecting tube of the lens on a hand camera can be easily fitted with a duplicator while the box camera with its lens set on the inside and nothing but a hole in the box does not have such advantages. A small piece of heavy cardboard can be made to produce the same results on a box camera as a first-cla.s.s duplicator applied to a hand camera.

[Ill.u.s.tration: Duplicator Attached to a Camera]

The cardboard is cut triangular and attached to the front end of the camera as shown in Fig. 1 with a pin about 1 in. above the lens opening. A rubber band placed around the lower end of the cardboard and camera holds the former at any position it is placed. A slight pressure of the finger on the point A, Fig. 2, will push the cardboard over and expose one-half of the plate and the same pressure at B, Fig. 3, will reverse the operation and expose the other one-half. Pins can be stuck in the end of the camera on each side of the lens opening at the right place to stop the cardboard for the exposure. With this device one can duplicate the picture of a person on the same negative.

--Contributed by Maurice Baudier, New Orleans, La.

** Optical Illusions [364]

The accompanying sketch shows two optical illusions, the first having a perfect circle on the outside edge

[Ill.u.s.tration: The Two Illusions]

appears to be flattened at the points A, and the arcs of the circle, B, appear to be more rounding. In the second figure the circle appears to have an oval form with the distance from C to C greater than from D to D. A compa.s.s applied to the circles in either figures will show that they are perfectly round.

--Contributed by Norman S. Brown, Chippewa Falls, Wis.

** Use of Kerosene in Polishing Metals [364]

Anyone who has polished a flat iron or steel surface with emery cloth knows how soon the cloth gums and fills up. The cloth in this condition will do little or no cutting. A simple remedy for this trouble is to use kerosene on the surface. The oil floats away a large part of the gumming substance and leaves the emery cloth sharp and clean to do the best work, also, it seems to act as a lubricant to keep particles of metal from collecting on the cloth and scratching or digging in the surface of the metal. A very light lard oil is equally good for this purpose, but not always easily obtained. A surface polished where oil or kerosene is used does not rust so easily as one polished dry, for the reason that a little oil remains on the metal.

Kerosene is the best to use on oil stones, being better than heavier oil. This oil readily floats away all particles of the feather edge that are liable to become loosened and forced into the stone. These particles of metal when stuck to the stone are the cause of spoiling it, as well as nicking the tools that are being sharpened. Keep the surface of the stone well oiled at all times to make the cutting free.

--Contributed by Donald A. Hampson, Middletown, N. Y.

** How to Make Lamps Burn Brightly [364]

For a good, steady light there is nothing better than a lamp, but like most everything it must have attention. After cleaning well and fitting it, place a small lump of camphor in the oil vessel.

This will greatly improve the light and make the flame clearer and brighter. If there is no camphor at hand add a few drops of vinegar occasionally.

** A Practical Camera for Fifty Cents [365]

By C. H. Claudy

I say for fifty cents, but really this is an outside estimate. If you possess a few tools and the rudiments of a shop, by which is meant a few odds and ends of screws, bra.s.s and nails, you can really make this camera for nothing.

The camera box is the first consideration, and for this a cigar box answers every purpose. It is better to use one of the long boxes which contain a hundred cigars and which have square ends.

This box should be cut down, by means of a saw and a plate, until the ends are 4 in. square. Leave the lid hinged as it is when it comes. Clean all the paper from the outside and inside

[Ill.u.s.tration: Construction of Camera Box]

of the box--which may be readily done with a piece of gla.s.s for a sc.r.a.per and a damp cloth--and paint the interior of the box a dead black, either with carriage makers' black or black ink.

Now bore in the center of one end a small hole, 1/4 in. or less in diameter. Finally insert on the inside of the box, on the sides, two small strips of wood, 1/8 by 1/4 in. and fasten them with glue, 1/8 in. from the other end of the box. Examine Fig. 1, and see the location of these strips, which are lettered EE. Their purpose is to hold the plate, which may be any size desired up to 4 in. square. Commercially, plates come 3-1/2 by 3-1/2 in., or, in the lantern slide plate, 3-1/4 by 4 in. If it is desired to use the 3-1/2 by 3-1/2 in. plates. which is advised, the box should measure that size in its internal dimensions.

We now come to the construction of the most essential part of the camera--the pin hole and the shutter, which take the place of the lens and shutter used in more expensive outfits. This construction is ill.u.s.trated in Fig. 4. Take a piece of bra.s.s, about 1/16-in.

thick and 1-1/2 in. square. Bore a hole in each corner, to take a small screw, which will fasten it to the front of the camera. With 1/4-in. drill bore nearly through the plate in the center, but be careful that the point of the drill does not come through. This will produce the recess shown in the first section in Fig. 4. Now take a No. 10 needle, insert the eye end in a piece of wood and very carefully and gently twirl it in the center of the bra.s.s where it is the thinnest, until it goes through. This pin hole, as it is called, is what produces the image on the sensitive plate, in a manner which I shall presently describe. The shutter consists of a little swinging piece of bra.s.s completely covering the recess and pin hole, and provided with a little k.n.o.b at its lower end.

See Fig. 3, in which F is the front of the camera, B the bra.s.s plate and C the shutter. This is also ill.u.s.trated in the second cross section in Fig. 4. In the latter I have depicted it as swung from a pivot in the bra.s.s, and in Fig. 3 as hung from a screw in the wood of the front board; either construction will be effective.

Lastly, it is necessary to provide a finder for this camera in order to know what picture you are taking. Make a little frame of wire, the size of the plate you are using, and mount it upright (see Fig. 5) on top of the camera as close to the end where the pin hole is as you can. At the other end, in the center, erect a little pole of wire half the height of the plate. If now you look along the top of this little pole, through the wire frame and see that the top of the little pole appears in the center of the frame, everything that you see beyond will be

[Ill.u.s.tration: Pin Hole and Shutter Construction]

taken on the plate, as will be made plain by looking at the dotted lines in Fig. 5, which represents the outer limits of your vision when confined within the little frame.

[Ill.u.s.tration: Explanation of Action of Pin Hole]

When you want to use this camera, take it into an absolutely dark room

[Ill.u.s.tration: Constructing a Finder for Camera]

and insert a plate (which you can buy at any supply store for photographers) in the end where the slides of wood are, and between them and the back of the box. Close the lid and secure it with a couple of rubber bands. See that the little shutter covers the hole. Now take the camera to where you wish to take a photograph, and rest it securely on some solid surface. The exposure will be, in bright sunlight and supposing that your camera is 10 in. long, about six to eight seconds. This exposure is made by lifting the little bra.s.s shutter until the hole is uncovered, keeping it up the required time, and then letting it drop back into place. It is important that the camera be held rigid during the exposure, and that it does not move and is not jarred--otherwise the picture will be blurred. Remove the plate in the dark room and pack it carefully in a pasteboard box and several wrappings of paper to protect it absolutely from the light. It is now ready to be carried to some one who knows how to do developing and printing.

To explain the action of the pin hole I would direct attention to Fig. 2. Here F represents the front of the camera, D the pinhole, AA the plate and the letters RR, rays from a lighted candle. These rays of course, radiate in all directions, an infinite mult.i.tude of them. Similar rays radiate from every point of the object, from light reflected from these points. Certain of these rays strike the pin hole in the front of the camera, represented here by RRRR.

These rays pa.s.s through the pin hole, and as light travels only in straight lines, reach the plate AA, forming an inverted image of the object, in this case a candle in a candlestick. Millions of rays are given off by every point in every object which is lighted by either direct or reflected light. To all practical purposes only one of these rays from each point in an object can pa.s.s through a minute opening like a pin hole. This being so, any screen which interrupts these selected rays of light will show upon it a picture of the object, only inverted. If that screen happens to be a photographically sensitive plate, which is protected from all other light by being in a dark box, upon it will be imprinted a photographic image which can be made visible by the application of certain chemicals, when it becomes a negative, from which may be printed positives. This camera is not a theoretical possibility, but an actual fact. I have made and used one successfully, as a demonstration of pin-hole photography.

** Use for an Old Clock [367]

Remove the hair spring of the clock, and fasten a spring to one end of the pawl and a small wire to the other end. Make a slit in the case of the clock opposite the pawl. Fasten the spring on the outside in any convenient way and pa.s.s the wire through the slit to an eccentric or other oscillating body. To make the dial, paste a piece of paper over the old dial, pull the wire back and forth one hundred times, and make a mark where the minute hand stops.

Using this for a unit divide up the whole dial. The hour hand has an inner circle of its own. Put the alarm hand at a little before twelve and wind the alarm. When the alarm is

[Ill.u.s.tration: Revolution Recorder]

unwound the hour hand starts on a new trip. The clock I used was put on an amateur windmill and when the hour hand went around once 86,400 revolutions or jerks on the wire were made, while the minute hand recorded one-twelfth of this number, or 7,200.

--Contributed by Richard H. Ranger, Indianapolis, Ind.

** Renewing Dry Batteries [367]

Dry batteries, if not too far gone, can be renewed by simply boring a small hole through the composition on top of each carbon and pouring some strong salt water or sal ammoniac solution into the holes. This kink is sent us by a reader who says that the process will make the battery nearly as good as new if it is not too far gone beforehand.

** Saving a Brush [367]

If a round brush spreads too much, slip a rubber band over the upper part of the bristles.