I’ve been asked many times by students and film-making enthusiasts to explain film to them. I decided to post more about film since the digital technologies are just a Google away! So, the best way to do this is to cover the basics. In this post I will explain the properties of film.
The emulsion, the top layer of the raw stock, is a light sensitive material. It is silver halide crystals suspended in gelatin. The variable size of crystals make emulsion sensitive to light. When exposed to light, a latent image is formed in the emulsion. When developed, the latent image becomes visible. The chemical solution of the developer reacts with the silver halide crystals to reduces them to metallic silver (opaque to light.) Using the fixer in the later stage of development, crystals that have not been exposed to light are removed by the fixer.
The areas of the emulsion most exposed to the light end up with greatest concentration of metallic sliver. These are the darkest areas when you project light through them. Areas with little light end up with less metallic silver and are more transparent. This is negative film. On the negative film all the brightness values of the original scene are reversed. Light becomes dark and dark becomes light!
The emulsion rests on the base layer which is firm and flexible support. This helps film run through the mechanics of filming, developing, and projecting with ease. In order to avoid reflection off the back of the film and re-expose the emulsion (halation), an antihalation backing is incorporated in a film layer. With modern film stocks, this halo effect is very minimal. But, you can spot some older films with a halo effect around a bright light source!
Next post we’ll talk about the film process.
©2012 babak sarrafan