Photography is the technique to produce images, usually by means of a camera.
From ancient times it was known that certain substances such as silver salts and asphalt, changed by light, and many had experimented with it; but an easy technique first developed by two Frenchmen, Niepce and Daguerre. The first died before the experiments were completed, but it succeeded Daguerre to complete them, and he published his findings in 1839. He let the image in camera obscura fall on a silvered copper plate that had been exposed to iodine vapor. The light changed jodsølvet, and when the plate is then exposed to mercury vapor condensed on those most where the light had seemed strongest, and who put mercury droplets closest. It uangrebne jodsølv bortvaskedes with sulfur under steeped soda, so that light could no longer change the plate. Were obtained beautiful images. They were seen best when a dark face reflected in them. Reflected a bright face in the plate, changed light to shadow, and the image was negative.
Method is improved, since it believes that use bromine and chlorine significantly shortened the time for the light. A major shortcoming was that these images could not be copied. Through Talbots works essentially was to copy drawings and natural objects was reached, the next step in camera history:
The camera obscura, used as photo camera, is a rectangular box, often to pull out like an accordion. It stands on a tripod, and on its front is a lens fitted. The backing is formed from a cut sheet of glass mats, in which the image falls on the object which is directed towards the lens. This picture, the photographer can consider carefully, as he wraps his head and the box in a dark cloth to extraneous light should not interfere. By making the lens can make the image very sharp. Image appears well, cover the lens, the frosted glass plate is removed and inserted in place of the photographic plate, which is enclosed in a flat wooden box (cassette) in order that no extraneous light to reach it. When in his place, uncovers Mon plate by pulling a cover up, and when the lens is exposed, the image falls on the plate. When lysvirkningen has lasted long enough, slid the lid.
The cartridge is then guided into a room, only lit by red light. This includes: the almost no actinic rays of light and is therefore harmless. The plate is of glass and prepared in advance by the smear with a solution of collodion in alcohol and ether, which also includes some iodine-bromsalte, and then treated with a silver solution, so that it is covered with iodine and bromsølv. Since the image falling on it, the silver salts is reduced; strongest where there is more light. There is thus a negative image on the plate, but it is so weak that it can hardly be seen. It can be induced by the plate are treated such. with the tannic acid, gallic acid or pyrogallussyre that the inks lyspåvirkede parts of the plate, and the unaffected silver salts is washed away with sulfur under saturated bicarbonate of soda, whereby the image is fixed.
Instead of collodion gelatin can be used. The gelatin is dissolved with or bromide in hot water, and thereto is added a silver solution. The precipitated finely divided bromsølv remain suspended in the gelatin solution, forms an emulsion with it. By cooking the emulsion or treat it with ammonia, we do it very sensitive to light, and when it melted the glass, created the so-called emulsion or gelatineplader. These can give such a susceptibility to light only needs to operate a small fraction of a second. They were used therefore, the instant photographs.
The image on the plate is negative, dark object in bright parts and bright in the dark. The different colors seem not equally strong. Red and yellow seem less and would therefore seem very dark blue and violet is stronger and appears almost white. By implicate a dye, eg. eosin in gelatin does one plate more susceptible to red and yellow light, and by inserting a yellow glass through which light falls, weakens the effect of the blue and violet, and thus can achieve images with the same lighting effects as the depicted object . The image reproduced on the plate placed on photographic paper and exposed to light. The paper is either covered with an albumen, providing a glossy finish or a layer of starch and then treated with silver solution. Silver salts blacked, strongest, where most light passes through, and when it happens at the points where the plate is brightest, exactly there where the object is darkest, is then given a positive picture of this. After exposure wash the unchanged silver salts away and the image is processed in a tonbad, a gold solution, which gives the image a more beautiful color. The dried pictures opklæbes and finished.
Gelatin has been treated with an acid potassium chrome red, becomes insoluble in water when exposed to light. Are stirred, a black dye in it, and is illuminated on the negative plate, the gelatin is insoluble in the bright parts. Wash the unaffected gelatin away with hot water, the picture back. It is used by kulfotografier.
Citric Acid jernforilte cyanjernkalium and red, which solutions are poured onto the paper, the color blue, the light work, and the image is fixed by washing with water. This method is used mostly by copying of machine drawings. The original drawing plotted on transparent paper - tracing paper - and in the chalk down the wet impregnated paper, and now it is exposed to light. They received as drawings in white lines on a blue background.