SIMPLEST FORM OF CAMERA.
A photographic image is formed on a plate, rendered sensitive to the action of light, by throwing upon it a re flection of the object or scene to be photographed. Those parts of the plate receiving the light portions of the image are affected by the different degrees of illumination they receive, the darker or shadow portions of the image making little or no impression. This being so, no light except that proceeding from the image itself must be allowed to fall upon the plate during exposure, or it will be affected all over, instead of only in parts, and a satisfactory picture will, therefore, not be obtained. The This washing consists of laying the print in the water. After a few moments pour this water away, and fill and soak again. After about twenty minutes' wash ing the print is finished,' and may be taken out and dried. This experiment illustrates the simplest process of making a print-out impression, and is the one used in engineers' offices for copying plans, etc. For general work such a process would not be satisfactory, as the image or picture is of a disagreeable colour, and appears sunken on the paper, the finer details being lost ; but as a preliminary experi ment it has the advantages of simplicity and cheapness. Let the student now take a step further and make a print-out im pression on albumen paper. For the proper working of this process some more apparatus will be necessary.
primary object of the camera is to provide a light-tight box, or dark chamber, in which the sensitive plate can be protected from all light except that which is reflected from the object or view being taken. If a tiny hole were pierced through one of the sides of a small light-tight box with a fine needle or tiny drill, it would be noticed that a candle-flame or gas-jet placed a short distance in front of the aperture would form its image on the side of the box opposite to the hole. By
opening the lid, and covering the head and the top of the box with a black cloth to exclude extraneous light, the representation of the candle-flame, or gas flame, would be plainly seen upside down. This may be better understood by refer ence to Fig. G. The rays of light, it will be seen, proceed in straight lines from all parts of the object, and, those which travel in the direction of the hole as shown, meet and cross each other, so that the continua ! tion of their course, on the other side of the aperture, results in the formation of a reversed image, when the rays reach a surface capable of reflecting them. Here are all the elements which go to the making admit enough light ; the image conse quently is very faint, and requires con siderable time to impress itself on the sensitive plate. This difficulty is removed by the employment of a lens, a piece of ground optical glass, or combination of glasses, having the surfaces curved to such a shape that rays of light passing of the simplest form of camera : a light tight box in which the plate may be ex posed, and an aperture through which may pass the rays of light which form an image or picture on the sensitive surface. At the present time " pinhole photography," as it is called, is practised by some amateurs, more especially by those who desire to through them are refracted, or bent aside, and caused to come together again inside the camera, forming an image or picture similar to that made by the tiny hole, but having the great advantage of being sharper and clearer, and, owing to the larger size of the lens opening, much better illuminated. To make this clearer, secure a " fuzzy " effect. It is, however, quite possible to get really good pictures without a lens, some results being possible with a pinhole which are obtainable in no other way, but the great drawback to the process is the necessarily prolonged ex• posure.