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This page provides information on the science used in all aspects of photography: the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film. 2005 : January - February - March - April - May - June - July - August - September - October - November - December- → Deaths in October 28: Richard Smalley 26: Emil Kyulev 24: José Azcona del Hoyo 24: Rosa Parks 23: Stella Obasanjo 22: Liam Lawlor 22: Shirley Horn 20: Endon Mahmood 17: Ba Jin 10: Milton Obote 7: Charles...
Photography is the process of making pictures by means of the action of light. ...
A camera is a device used to take pictures (usually photographs), either singly or in sequence, with or without sound recording, such as with video cameras. ...
Photographic lens One of Canons most popular wide angle lenses - 17-40 f/4 L The zoom lens of the Canon Elph A photographic lens (or more correctly, objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images...
The optical system
Law of Reciprocity
- Main article: Reciprocity (photography)
Exposure = Aperture x Shutter Speed x Film ISO
The law of reciprocity is the golden rule of photography—it defines the relationship between time, aperture, and film speed with respect to an even exposure. Changes to any one of those three elements are done in units known (in photographer jargon) as "stops." A stop is a factor of 2, and to halve the amount light is to "close down a stop," while doubling the light is "opening up a stop." Light is most easily controlled through the use of the camera's aperture settings (f-stops), but it can also be regulated by adjusting shutter speed or simply choosing faster or slower film.
In photography, reciprocity refers to the relationship between different choices of aperture and shutter speed that result in identical exposure. ...
In optics, an aperture is something which restricts the diameter of the light path through one plane in an optical system. ...
Film speed is the measure of a photographic film stocks sensitivity to light. ...
A photograph with an exposure time of 25 seconds In photography, exposure is the total amount of light allowed to fall on the sensor (photographic film or CCD) during the process of taking a photograph. ...
A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ...
The shutter speed dial of a Fujica STX-1. ...
Film refers to the celluloid media on which movies are printed. ...
Note however that increasing the f-stop also limits the resolution due to the Diffraction (aperture) limit.
Reciprocity calculations are simply done: If you open up a stop with one of the three factors, you must close down a stop in another one, thus maintaining the balance. If you had an exposure of 1/60 at f/16 (using ISO 100 film) but you really wanted a shallower depth-of-field, you could open up your aperture to f/4 (+4), but you would need to adjust your shutter-speed as well by (-4) down to 1/1000.
 Table comparing exposure with aperture and shutter speed. Image File history File links Law_of_Reciprocity_table. ...
Image File history File links Law_of_Reciprocity_table. ...
Lenses - Main article: Photographic lens
A photographic lens is composed of several lenses, to reduce the effects of chromatic aberration, coma, spherical aberration, and other aberrations and to allow focusing, and possibly zooming capabilities. A simple example is the Cooke triplet, which was used in early cameras, but has since been replaced by more complex systems. Another, the Angenieux retrofocus allows the distance between the last lens and the film to be larger than it would be otherwise. This design is necessary for wide angle lenses on manual cameras, since otherwise the last lens would need to be so close to the film so as to interfere with the mirror. Aberrations generally can be reduced by using a small aperture to prevent light from striking the outer parts of the internal lens elements, since aberrations generally get worse further from the central axis of the lens. Aberrations can be reduced dramatically by using an aspheric lens, but these are more complex to grind than spherical or cylindrical lenses. However, with modern manufacturing techniques the extra cost of manufacturing aspherical lenses is decreasing, and small aspherical lenses can now be made by molding, allowing their use in inexpensive consumer cameras. Fresnel lenses are not used in cameras even though they are extremely light and cheap, because they produce poor image quality. Photographic lens One of Canons most popular wide angle lenses - 17-40 f/4 L The zoom lens of the Canon Elph A photographic lens (or more correctly, objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images...
A lens. ...
Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. ...
In optics (especially telescopes), the coma in an optical system refers to monochromatic aberration inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted. ...
Focal plane Longitudinal sections In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a lens or mirror near its edge, in comparison with those that strike nearer the center. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
The Cooke triplet is a photographic lens design designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by Cooke of York. ...
The Retrofocus photographic lens was invented in France in 1950 by Angenieux, and is characterized by a large negative meniscus lens element up front followed by four or five small elements in the rear. ...
In photography and cinematography, a wide-angle lens is a lens whose focal length is shorter than the focal length of a normal lens. ...
An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder. ...
Fresnel Lens displayed in a Paris museum A Fresnel lens is a type of lens invented by Augustin-Jean Fresnel. ...
See also the diagram Movement of lenses in an afocal zoom system under Zoom lens. It is harder to correct for chromatic aberration with zoom lenses, as they must be calibrated to focus over a range of focal lengths. Zoom lenses will also generally have a smaller range of f-stops than fixed focal length lenses. A Canon Inc. ...
Focal length The focal length of any lens is defined as the distance from the rear principal plane of the lens to the point at which rays of parallel light incident on that lens will be focussed. Since modern photographic lenses are almost always constructed from several simple lenses, the effective focal length of the lens is a complicated function of the optical powers of the surfaces of these simple lenses and the relative distances between them. The greater the focal length of a lens, the greater the magnification of the image on the focal plane. This increase in magnification is gained at the cost of reduced viewing angle and decreased image brightness, since the same light is spread over a larger area in the image plane. The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ...
The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system, which help in the analysis of its paraxial properties. ...
A simple lens is a lens consisting of a single simple element. ...
Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. ...
Aperture The amount of light admitted to a camera is controlled by an iris or diaphragm inside the lens. This diaphragm is the aperture stop of the camera. Its opening is typically manually or automatically variable, with the size of the opening represented by the f-number. F-numbers typically vary in discrete steps, called f-stops. The f-number is equal to the ratio of the focal length to the diameter of the entrance pupil of the lens. For a given lens configuration, the pupil diameter is proportional to the physical diameter of the opening in the diaphragm. A 35mm lens set to f/8; the diameter of the heptagonal diaphragm opening is 4. ...
In optics, an aperture is something which restricts the diameter of the light path through one plane in an optical system. ...
A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ...
In an optical system, the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light. ...
Depth of field and Bokeh When a camera lens is focused to image an object some distance away onto the film or detector, objects some distance closer to and farther away from the camera are also approximately in focus. The range of distances that are nearly in focus is called the depth of field. Depth of field generally increases with decreasing aperture diameter (increasing f-number). The unfocused blur outside the depth of field is sometimes used for artistic effect in photography. The subjective appearance of this blur is known as bokeh. An example of very shallow depth of field in a macro photograph. ...
The astounding bokeh of a Helios-40 lens A photograph of jonquil flowers with background bokeh Compare a photograph of jonquil flowers with low background bokeh Bokeh (from the Japanese boke ã¼ã‘, blur) is a photographic term describing the subjective aesthetic qualities of out-of-focus areas in an...
If the camera lens is focused at or beyond its hyperfocal distance, then the depth of field becomes large, covering everything from half the hyperfocal distance to infinity. This effect is used to make "focus free" or fixed-focus cameras. Hyperfocal distance is a distance used in optics, especially photography. ...
The word infinity comes from the Latin infinitas or unboundedness. It refers to several distinct concepts which arise in theology, philosophy, mathematics and everyday life. ...
A focus free lens is a photographic lens whose focal point is fixed at its hyperfocal distance. ...
See also Circle of confusion. The depth of field is the region where the size of the circle of confusion is less than the resolution of the human eye. ...
Section references:
Motion blur Generally a tripod is used when the magnification is high or the picture is taken in low light. Tripod can refer to: A tripod supporting a television camera. ...
Physics of...
Autofocus The autofocus system in modern SLRs uses a sensor in the mirrorbox to measure contrast. The sensor's signal is analyzed by an ASIC, and the ASIC tries to maximize the contrast pattern by moving lens elements. Autofocus (or AF) is a feature of some optical systems that allow them to maintain correct focus on a target. ...
The single-lens reflex (SLR) is a type of camera that uses a movable mirror placed between the lens and the film to project the image seen through the lens to a matte focusing screen. ...
A detector is a device that detects or measures some phenomenon or stimulus, and produces some signal in response. ...
An ASIC (application-specific integrated circuit) is an integrated circuit (IC) customised for a particular use, rather than intended for general-purpose use. ...
The ASICs in modern cameras also have special algorithms for predicting motion, and other advanced features.
Workings of a typical manual camera system
Effects limiting resolution (detail)
Focus Focus is the tendency for light rays to reach the same place on the CCD or film, independent of where they pass through the lens. For clear pictures, the focus is adjusted for distance, because at a short object distance the rays reach different parts of the lens with different angles. In modern photography, focussing is often accomplished automatically. The focus or image point is the point where light rays, originating from a point in the object, converge [1]. The principal focus or focal point of a lens or parabolic mirror is the point onto which collimated light parallel to the axis is focused. ...
Aberration - Main article: Aberration in optical systems
Aberrations are the (ray optical rather than diffraction) blurring and distorting properties of an optical system, beyond first order focus. The better the lens, the smaller its aberrations. This article needs to be cleaned up to conform to a higher standard of quality. ...
Spherical aberration is the dependence of the focal length of a spherical lens on the distance from its center. It is compensated by designing a multi-lens system or by using aspheric lenses.
Chromatic aberration is the dependence of the optical properties on color (wavelength), due to dependence of the refractive index of a lens on color. Blue light is generally bent more than is red. Simple chromatic aberration is the difference in focal length for different colors. There are also higher order chromatic aberrations, such as the dependence of magnification on color. Chromatic aberration is compensated by using lens elements made out of different materials, carefully designed so that their chromatic aberrations cancel.
Curved focal surface is the dependence of the first order focus on the position on the film or CCD. This can be compensated with a multiple lens optical design, but curving the film has also been used.
How electron overflow in CCDs can lead to blurring and fringing effects A specially developed CCD used for ultraviolet imaging in a wire bonded package. ...
Film Grain Resolution Black & White film has a "shiny" side and a "dull" side. The dull side is the emulsion, a gelatin that suspends an array of Silver Halide crystals. These crystals contain silver grains. The size of the silver grains determine both (a) how sensitive the film is to light exposure, and (b) how fine or grainy the negative (and any subsequent prints made from that negative) will look. Larger grains mean faster exposure but a grainer appearance; smaller grains are finer looking but take more exposure to activate. (The graininess of film is represented by its ISO factor -- generally a multiple of 10 or 100. Lower numbers = finer grain but slower film, and vice versa.)
Diffraction limit When light is incident on an object with a dimension comparable to that of its wavelength, then optical diffraction occurs. Diffraction effects can be very pronounced if the diffracted light is both coherent and monochromatic, but are typically quite small, and are dwarfed by other optical abberations. The diffraction limit is an important concept in lens design, however. Since diffraction cannot be eliminated, the best possible lens for a given operating condition is one that produces an image whose quality is limited only by diffraction. Such a lens is said to be "diffraction limited". Normally this means that optical aberrations have been reduced to the point where they can be ignored compared to the slight blur due to diffraction. A more sophisticated lens will be diffraction limited over a wider range of operating conditions. To meet Wikipedias quality standards, this article or section may require cleanup. ...
Like any other wave, light spreads out when it passes through small apertures. (This is why things look streaky when looking through a window screen.) For visible light photography, this turns out to be comparable to other resolution limiting effects. The spot size on the CCD or film is proportional to the f number, so the overall detail in a photograph is proportional to the size of the film or CCD divided by the f number, which is the aperture size. For a 35 mm. camera with f 11, this corresponds to scanning width of two or three thousand pixels.
An other way to put it is that a camera cannot resolve two distant points unless their path lengths to the two sides of the open lens aperture differ by at least a half wave length. Otherwise they will be both in phase at the same point on the film or CCD.
This an important reason that the next generation of cell phone cameras will need to focus. A non-focussing camera needs a large depth of field, but on a small scale this makes the aperture very small which limits the resolution.
Contribution to noise (grain)
Quantum efficiency As is well known to communications engineers, light, like everything else, comes in particles. The energy of a particle (photon) is the frequency times Plank's constant. A fundamental property of any photographic method is how many particles it has to catch, on the average, for each one counted. A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ...
Film This is a way of understanding the "grain" in film pictures. The chemistry limits the fraction of light particles that cause chemical change. To make the film sensitive, the silver compounds are in particles so that one captured photon turns a whole grain dark.
CCDs and other photodiodes Photodiodes are back-biased semiconductor diodes, in which an intrinsic layer with very few charge carriers prevents current from flowing. Depending on the material, a light particle (photon) has enough energy to raise one electron from the upper full band to the lowest empty band. The electron and the "hole", or empty space were it was, are then free to move in the electric field and carry current, which can be measured. The fraction of incident photons that produce carrier pairs depends largely on the semiconductor material.
Photo-multipliers Photo-multipliers, which are vacuum phototubes with amplification by accelerating the photoelectrons so that they knock more electrons free, are among the most sensitive light detectors, but are not well suited to photography.
Aliasing Aliasing can occur in optical and chemical processing, but it is more common and more easily understood in digital processing, where it occurs whenever an optical or digital image is sampled or re-sample at a rate which is too low for its resolution. Some digital cameras and scanners have anti-aliasing filters to reduce aliasing by intentionally blurring the image to match the sampling rate. It is common for film developing equipment used to make prints of different sizes to increase the graininess of the smaller size prints by aliasing. In statistics, signal processing, and related disciplines, aliasing is an effect that causes different continuous signals to become indistinguishable (or aliases of one another) when sampled. ...
In digital signal processing, anti-aliasing is the technique of minimizing aliasing (jagged or blocky patterns) when representing a high-resolution signal at a lower resolution. ...
It is usually desirable to suppress both noise such as grain and detail of the real object that are too small to be represented at the sampling rate.
Chemistry of Film Development
Film Understanding silver halide grains is absolutely key to photography. You probably know that light comes in two forms, waves or photons. Silver halide crystals detect the photons when they hit the film surface. Silver halide crystals are formed from silver nitrate (AgNO3) and one or more of the halide salts – silver chloride (AgCl), silver bromide (AgBr), silver iodide (AgI), and Potassium Bromide (KBr). Silver nitrate is arguably the most important inorganic silver salt. These salts are suspended in a gelatin on the emulsion side of the film.
The gelatin has many properties that make it especially useful in photographic emulsions. First, it serves as a protective colloid for the light-sensitive silver halide crystals that make up the active part of the emulsion. Second, it is transparent and very pure, allowing light to expose the emulsion without distorting it. Third, it is water permeable, so that the developing solutions can react with the exposed silver halide crystals to form the final image. Fourth, it has good adhesion to its base and is easy to coat uniformly on that base. Many attempts have been made to use inorganic replacements for gelatin, but none have been found to be effective, and there is not a single commercially available paper that does not use gelatin. Film base is a transparent substrate which acts as a support medium for the photosensitive emulsion that lies atop it. ...
At this point, the emulsion maker has two solutions, one of silver nitrate in distilled water and the other of a halide in gelatin (I will use sodium chloride for this example.) The following steps have to be carried out under red light only, as the solution becomes light-sensitive at this point. The two solutions are then mixed, forming silver chloride and sodium nitrate (AgNO3 + NaCl = AgCl + NaNO3). The silver chloride precipitates, but is held suspended by the gelatin. The sodium nitrate is soluble and can be washed away.
The emulsion then goes through a process called Ostwald Ripening. This is a very interesting process and it determines the grain size (ISO speed). At the beginning, the grains (groups of particles of silver chloride) are fairly small, so small that the grains are hard to see with the naked eye. If the maker of the emulsion wants a slow, fine-grained emulsion, he would stop the process right away (by cooling the emulsion.) However, if a faster emulsion is desired, he would let the process continue. At this point, the smaller grains dissolve into solution and re-form themselves on the larger grains. Thus, the large grains get larger and the small grains get smaller.
The emulsion can then be coated onto the base. Most commercial papers have hardeners added to them at this point for several reasons, but mainly because they prevent the gelatin in the emulsion from liquefying and coming off of the base when the paper is developed. Depending on the specifics of the desired paper, other ingredients may also be added at this time. They serve a variety of purposes including slowing down the emulsion, speeding up the emulsion, adjusting the pH to a desirable level (6.0-6.5), increasing contrast, and more.
(some info above sourced from: [1] )
Developing The developing agent must be a reducing agent that can discriminate between the exposed and the unexposed grains of the emulsion. Two organic compounds have been proven to perform this task exceptionally well, and they are used almost exclusively, either alone or in combination, in photographic developers. They are hydroquinone (C6H4(OH)2) and p-menthylaminophenol sulfate ((C7H9NO)2SO4) (Kodak Elon developing agent). The developing agent in the developer solution is ionized, and these ions supply electrons to the silver ions of the exposed silver chloride grains, reducing them to solid silver. The solid silver is what forms the final and permanent black image. The chlorine and the developer are simultaneously oxidized. Sodium sulfite (Na2SO3) is present in the developer solution and reacts with these byproducts to form clear and colorless compounds that will not stain the final image.
(some info above sourced from: [2] )
Stop-Bath & Fixer After development, the image is not yet stable. It has two more steps to go through before becoming permanent: stop bath and fixer. Stop bath serves to stop the developing. The stop bath is an acidic solution that reduces the pH of the developer remaining on the emulsion enough so that the development stops. The fixer makes the print permanent - one can spot a print that was not fixed properly by noticing that it has faded and the white areas have turned brownish. While silver halides are not soluble in water, they are soluble in sodium thiosulfate (Na2S2O3), which is the main component of fixer solutions. The sodium thiosulfate dissolves out the halide (chlorine in our example) and then reacts with the silver ion in the following way: Ag+ + 2(S2O3--) = Ag(S2O3)2---. A hardener is usually also present in the fixer to prevent swelling of the emulsion during subsequent washings as well as to make it more durable overall. The film or paper is then washed to ensure that no chemicals are remaining on it. Any remaining chemicals would cause discoloration over time. Many of the stains that can be seen on old black and white photographs are a result of improper fixing or washing following development. However, with the knowledge that we now have about the permanence of black and white emulsions, a photograph can last almost indefinitely if it has been processed correctly.
(some info above sourced from: [3] )
Polaroids
Conditions with other practical and scientific concerns to the photographer Astrophotography is a specialised type of photography that entails making photographs of astronomical objects in the night sky such as planets, stars, and deep sky objects such as star clusters and galaxies. ...
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