A Manual Of Photography

THE DISCOVERT OE M. DAGUERRE. 41 teen inches. M, is a stop a short distance from the ten», the obiect of which is to cut off all those rays of light wInch do not come directly from the object to which the camera is directed. This instrument reverses the objects ; that which is Mothe « in nature being to the left in the photograph. This can be remedied by using a mirror outside as KJ, n figure 9.T arrangement, however, reduces ie TKU1 course increases the time of the operation one-third. It will of course be adouted only when there is time to spare. After having placed the camera in front of the landscape or any object of which we desire the representation, our first to adjust the plate at such a distance from the lens, that a neat and sharply defined picture is produced. This is, of course, done by the obscured glass. The adjustment being satisfactorily made, the glass is removed, and its place supplied by the frame containing the prepared plate, and the whole secured by the screws. The doors are now opened by means of the half circles, and the plate exposed to receive the picture. The length of time necessary for the pro- duction of the best effect, vary- ing with the quantity of light, is a matter which requires the ex- ercise of considerable judgment, particularly as no impression is visible upon the tablet when it is withdrawn from the camera. At Paris this varies from three to three o’clock. A drawing to thirty minutes. The most favourable time is from seven ., which, in the months of June and July, may be taken in three or four minutes, will require five or six in May or August, seven or eight in April and September, and so on, according to the season Objects in shadow, even during the brightest weather, will require twenty minutes to be correctly delineated. From what has been stated, it will be evident that it is impossible to fix, with any precision, the exact length of time necessary to obtain photographic designs ; but by practice we soon learn to calculate the required time with considerable correctness. I he latitude is, of course, a fixed element in this calculation. In the