How Photography Works (Film Photography) A Lecture By: AMIT CHAWLA

Photographic Process Photographic Process can be broadly divided into 3 major steps: – Ray optics and How light forms images – Film Processing – Print Processing

How light forms images

Concept of PinHole Imaging

Refraction by Converging Lens kisalev/java/clens/index.html

Converging Prisms In practical photography & in cameras instead of single Convex Lens we use number of PRISMS with combined convergence effect.

Converging Prisms in Professional Lenses In professional Lenses not a single convex lens or a convex prism, instead a combination of many lens elements are combined together to achieve an overall converging effect.

How light forms image on Film Cross section of Black and White Negative Films. 1. Overcoating 2. Emulsion 3. Base 4. Antihalation backing 5. Noncurl coating

1. Overcoating The overcoating protects film from friction, scratches, or abrasions before development. The overcoating is a clear, gelatin layer that is sometimes called the antiabrasion layer.

Emulsion & Base 2. Emultion - Thin layer of gelatin that suspends and supports the light-sensitive silver halides. 3. Base -This supports or holds the emulsion in place. The base may be transparent, translucent, or opaque, depending upon how the recorded image is to be used. The base is generally made of a cellulose acetate.

4. Antihalation backing- The antihalation backing prevents light from reflecting from the base back into the emulsion. The antihalation dye is someti mes incorporated in the anticurl backing. The dye used to eliminate halation is a color to which the emulsion is least sensitive. This dye is water soluble and is com- pletely dissolved during processing.

5. Noncurl coating Noncurl coating is a hardened gelatin, about the same thickness as the emulsion, and is applied to the back of the film. A film emulsion swells when wet and shrinks when dry. This contraction produces a strain on a film base because it is highly flexible. The noncurl coating prevents the film from curling during the drying process.

Structure of AgBr This lattice contains ions of bromine and silver (Br- and Ag+). When incoming light hits this crystal lattice, the extra electron contained on the bromide ion is released.

Reaction of photons on AgBr This free electron then jumps from the now bromine atom to the positively charged silver ion. As a consequence of this electron coming into contact and binding to the silver ion, the silver ion is transformed into metallic silver (Ag). This creates a small region of silver metal.