Analog photography

Green Sensitive Layer containing Magenta Coupler Interlayer ------------------- 

A color correction may also be achieved by using filters. Table 3.1 shows the type of filter used by professional photographers to achieve accurate color reproduction. The required filter depends on the type of illuminant and also on the type of film. The type of light source can be described using the temperature of a black-body radiator. A black-body radiator is a light source whose spectral power distribution depends only on its temperature (Jacobsen et al. 2000). The color temperature of a fight source is the temperature of a black-body radiator, which essentially has the same spectral distribution in the visible region. The concept of a black-body radiator is formally introduced in Section 3.5. 

Additional postprocessing may be done on a computer. The color negative can be either digitized using a film scanner or we can develop color prints that can then be digitized 

Light Source Filter for Temperature (K) Tungsten Film Daylight Film  

---

Alternative Photography, www.alternativephotography.com Analog Photography Users Group, www.apug.org... 

The analog photography community is well-versed with the fact that silver halides are tunable band gap semiconductors. Thus the photoactivity of AgCl can be tuned from the UV into the visible light region by a process known as self sensitization, which is due to the formation of Ag clusters during the photoreaction. The formation of these clusters introduces new levels within the forbidden gap that can now be populated by visible light (Fig. 7). 

Dry-Film Resists Based on Radical Photopolymerization. Photoinitiated polymerization (PIP) is widely practiced ia bulk systems, but special measures must be taken to apply the chemistry ia Hthographic appHcations. The attractive aspect of PIP is that each initiator species produced by photolysis launches a cascade of chemical events, effectively forming multiple chemical bonds for each photon absorbed. The gain that results constitutes a form of "chemical amplification" analogous to that observed ia silver hahde photography, and illustrates a path for achieving very high photosensitivities. 

Eventually, the ray of light will enter the lens of the camera. In the back of the camera, we either have an analog film or a sensor array that measures the incident light. We will look at how the analog film responds to light in the next section. Digital photography is addressed in Section 3.2. 

The term dye is frequently used to describe two major chemical classes colorants that affect the perceived color of other materials, and transducers that accept photons of a specific wavelength and generate a technical response that can take on a number of forms. Dyes as colorants are not total analogs to visual photo-reception, but the chemistry of photography is. This field has nearly all of the same constraints and requirements as does vision chemistry. It can be very instructive to review dye chemistry as it apphes to photography and transition that analog to the natural vision chemistry arena. 

Most of the molecules of interest in vision and biology are prepared lyotropically. There are three main classes, the nematic, the smectic, and the cholesteric-nematic (frequently simplified to just cholesteric) When deposited on a substrate, the chromophores of vision assume a stmcture of smectic class. This class is further subdivided into types A through H. Type A liquid crystals have their major molecular axis perpendicular to the surface of the film. Type C crystals have their major molecular axis at some other angle. Assuming an analogy of similar chromophores in photography, it is most likely that the chromophores of vision are of type C. 

Another important contribution of radiation chemistry in photography was the enhancement of the sensitivity of photographic emulsions. The primary effect of photon absorption by silver halides is the formation of an electron-hole pair. However, because of the very fast and efficient electron-hole recombination and oxidation by hole of the newly formed silver atoms, the conversion yield of light is very low. The analogy with HO oxidation processes occurring in irradiated solutions led to the use of the same scavenging method to inhibit the electron-hole pair recombination and the oxidation by the... 

Substituted p-phenylenediamines are developers used in color photography. They include A,A-diethyl-p-phenylenediamine (p-diethylaminoaniline) monohydrochloride, its toluidine analog, A-p-anilinopyrrolidine, 4-amino-A-/S-methanesulfonamidoethyl-m-toluidine sesquisulfate monohydrate and 4-amino-3-methyl-A-ethyl-A-(/9-hydroxy -ethyl)aniline sulfate. 

Johnston, Sean F. Absorbing New Subjects Holography as an Analog of Photography. Physics in Perspective vo. 8, issue 2 (2006) 164-188. Provides the history and background in the development of holography and examines the cultural influences on the field. 

---