Collodion photography

In Daguerre, the silver plate photography method is to expose the steel plate coated with silver iodide in a black box, then develop it with mercury vapor and fix it with salt. This method is actually a negative metal image, but it is very clear and can be preserved forever. Because the exposure time takes about 20 to 30 minutes, early photography often takes pictures of still lives, landscapes and portraits.

Carl Porter, an English inventor, was the pioneer of negative film from negative film to positive film. 1835, he began to try out drawings coated with silver chloride or silver nitrate as photosensitive materials, took negative photos in the camera, and then printed them by sunlight. He named his method "Carol Photography"

The photosensitive materials used in Carlo Photography are different from those used in Daguerre Photography in the formation of film base and photosensitive silver halide. He used high-strength paper as the carrier of the sensitizer. Before shooting, he soaked the paper in sodium chloride solution, then dried it, and then soaked it in concentrated silver nitrate solution, so that the sodium chloride and silver nitrate on the paper base fully reacted to generate silver chloride with photosensitive effect (NaCl+AgNO3 = AgCl+Nano4). Then he put the sun-dried paper in a camera and fixed it with sodium chloride solution after exposure. Overlap this negative with another unexposed photosensitive paper, fully expose it, and fix it to get a photo with the same light and shade, direction and object image.

The photosensitive materials used by Daguerre and Talbot have a common shortcoming, that is, the sensitivity is very low, and the photosensitive time often takes several minutes, so the choice of subjects is greatly limited. It was not until Archer invented "collodion photography" in 185 1 that photographic photosensitive materials made a qualitative leap and replaced those used by Daguerre and Talbot.

Collodion is a colloidal emulsion made by dissolving collodion (nitrocellulose) in alcohol (ethanol) and ether. It is a good adhesive for photosensitive materials. Sodium iodide (NaI) and a small amount of potassium bromide (KBr) are mixed with collodion evenly, then coated on a clean glass plate, and then the glass plate is put into silver nitrate solution, so that silver nitrate reacts with silver iodide and potassium bromide on the glass plate to generate silver iodide and silver bromide crystals with photosensitive effect. This kind of glass-based "collodion" photosensitive material can be photographed immediately. After shooting, use pyrogallol as developer and hypo as fixing agent, and develop immediately. After drying, you can get a negative with the opposite light and shade to the real thing.

The biggest advantage of collodion photography is that it can shoot clear images like Daguerre photography, but the cost is less than that of Daguerre photography110. At the same time, like Talbot photography, it can be printed repeatedly through paper inspection, but the picture quality is far finer than Talbot photography. It has advantages and disadvantages, and the photosensitive speed is higher than that of Daguerre photography or Talbot photography. In bright sunlight, the exposure time only takes 15 seconds to 1 minute, so it has been popular all over the world for more than 20 years since it came out in 185 1 year, which has become an important historical period in the history of photography.

The only disadvantage of collodion photography is that shooting and developing must be completed about 20 minutes before collodion drying. Because collodion is impermeable after drying, the liquid medicine can not play its role, so it is also called "wet plate" photography. This shortcoming has brought great trouble to photographers, especially when they go out to shoot. In addition to cameras and tripods, you must also carry washing equipment such as chemicals and darkroom tents, which makes many photographers afraid to use them.

The appearance of digital photography is a great leap in photography technology, which exposes the shortcomings of traditional film photography and in turn confirms the advantages of traditional film photography.

Compared with digital cameras, traditional film cameras have temporarily incomparable advantages in color reproduction, clarity, reaction speed, power consumption, storage mode and many other aspects.

Digital cameras have to go through complicated electronic operations, while simple electronic operations or purely mechanical operations of traditional cameras omit complicated processes, which can support quick start-up and shooting.

Digital cameras consume a lot of electricity, while traditional cameras are relatively small. Under special circumstances such as outdoor photography, once the memory card of digital camera is used up, there is nothing to do, so it is much more convenient to buy film.

The combination of traditional film photography, digital photography and computer image processing technology is the correct direction of future photography development.