Photographic film-based photography…

Digital photography was not commercially available until the 90s; until then most pictures (and movie pictures) were created using sheets of transparent, plastic film-base, coated on one side with a gelatin- emulsion containing microscopically small light-sensitive silver halide crystals. When this side is exposed to a short flash of light (let in by a lens of some kind), a very slight chemical change is produced, proportional to the amount of light absorbed by each crystal (with the characteristics of the crystals determining sensitivity, contrast and resolution. The chemical change will create an invisible latent image in the emulsion, which can be chemically developed into a visible photograph, typically through a mixture of chemical compounds prepared as an aqueous solution (black + white) – an alkaline agent such as sodium carbonate, borax, or sodium hydroxide to create the appropriately high pH, sodium sulfite to delay oxidation of the developing agents by atmospheric oxygen and the developer itself which can vary but is generally built up of metol (monomethyl-p-aminophenol hemisulfate), phenidone (1-phenyl-3-pyrazolidinone), dimezone (4,4-dimethyl-1-phenylpyrazolidin-3-one), and hydroquinone (benzene-1,4-dill).

MetolStructureRevised 400px-Phenidone.svg13047-13-7Hydrochinon2.svg

For colour photography the process is a little bit more complicated, requiring a polyester film base, onto which multiple emulsions are coated. Each layer is only sensitive to a certain colour of visible light, or serves as a filter of certain colours, typically composed of dyes or colloidal silver. Other layers will not be sensitive to light at all and will be top-coated with UV blocking layers or anti-scratch coatings, or may be placed to separate various light-sensitive emulsions.  As for the development, dye couplers in the emulsion react with the oxidized colour developing agent in the developer solution to generate the visible dyes. This is the C-41 process which is probably the most common form of development, but there are distinctive alternatives.

C-417

Whilst some people (including photographers) prefer the look of film, digital photography is significantly more practical, allowing you to instantly view, edit, print and store an image without any chemical processing. The look of film still evidently has its advantages with spatial resolution. Digital sensors are generally arranged in a rectangular grid pattern, making images susceptible to moire pattern artifacts, whereas film is not affected by this because of the random orientation of its grains. Film and digital work each provide a wide range of performance in this regard, overlapping but with film tending to higher resolution because of the size of the imaging area with medium-format and large-format films. These can record higher resolution images than current top-of-the-range digital cameras (A medium format film image can record an equivalent of approximately 50 megapixels whilst medium-format digital provides 40, usually).

There are issues with trick photography when it comes to film; producing a first generation image, which contains only the information admitted through the aperture of the camera (this is actually useful for things where the authenticity of an image is important, like passport or visa photographs). There are other limitations with film such as speed (digital cameras being capable of much higher speeds), the ongoing expenses of film stock and developing the images, and the general limitations of the amount of images you can take with one roll of film (up to 36).

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