Class 004 photography working 1-1

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  • Working of Photography can be broadly classified into 3 sections / subparts: Ray Optics & How Light is captured on Film Film Processing Print Processing
  • Nearly all forms of photography are based on the fact that certain chemicals are photosensitive— that is, they change in some way when exposed to light. Photosensitive materials abound in nature; plants that close their blooms at night are one example. The films used in photography depend on a limited number of chemical compounds that darken when exposed to light. The photographic process can be broadly divided into 3 major steps: Ray optics and how light is captured on film Film Processing Print Processing
  • How light forms images Suppose you set up and illuminate a subject, and just face a piece of paper (or film) towards it. You will not of course see any image on the sheet. The trouble is that every part of your subject is reflecting some light towards every part of the paper surface. This jumble of light simply illuminates it generally. One way to create order out of chaos is to restrict the light, by adding between subject and paper a sheet of opaque material containing a pinhole. Since light travels in straight lines, those light rays from the top of the subject able to pass through the hole can only reach the bottom part of the paper and vice versa.
  • As light from lower parts of the subject only reaches the top of the paper and the light passing through the hole can only reach the bottom part of the paper; your paper sheet shows a dim, rather fuzzy upside-down representation of the subject on the other side of the pinhole. The best way to see a pinhole image is to be in a totally darkened room, with black paper over the window facing a sunlit scene outside. How can we overcome the problems of fuzzy and dim image?? Well the answer to this question is a CONVEX LENS.
  • The image formed by a converging lens can be made using only three principal rays. Ray 1 is the ray which travels parallel to the axis and after going through the lens it passes through the focal point. Ray 2 passes through the center of the lens. Ray 3 goes through the focal point and then travels parallel to the axis after passing through the lens. Thus any point on the object can be mapped, using the rays above, into a corresponding point on the image. This point is located on the intersection of the rays. Combining these three, we can get a sharp inverted image on the paper or film placed behind the convex lens.

Transcript

  • 1. How Photography Works (Film Photography) A Lecture By: AMIT CHAWLA
  • 2. Photographic Process Photographic Process can be broadly divided into 3 major steps: – Ray optics and How light forms images – Film Processing – Print Processing
  • 3. How light forms images
  • 4. Concept of PinHole Imaging
  • 5. Refraction by Converging Lenshttp://www.physics.uoguelph.ca/applets/Intro_physics/kisalev/java/clens/index.html
  • 6. Converging Prisms In practical photography & in cameras instead of single Convex Lens we use number of PRISMS with combined convergence effect.
  • 7. Converging Prisms in ProfessionalLenses 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.
  • 8. How lightforms imageon Film Cross section of Black and White Negative Films.  Overcoating  Emulsion  Base  Antihalation backing  Noncurl coating
  • 9. 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.
  • 10. Emulsion & Base2. 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.
  • 11. 4. Antihalation backing- The antihalation backing prevents light from reflecting from the base back into the emulsion. The antihalation dye is sometimes 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.
  • 12. 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.
  • 13. http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Mike_Kudenov%20/Film.htm 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.
  • 14. http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Mike_Kudenov%20/Film.htm 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.