Science of photography


The science of photography is the use of chemistry and physics in all aspects of photography. This applies to the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film in order to take and develop pictures properly.

Optics

Camera obscura

The fundamental technology of most photography, whether digital or analog, is the camera obscura effect and its ability to transform of a three dimensional scene into a two dimensional image. At its most basic, a camera obscura consists of a darkened box, with a very small hole in one side, which projects an image from the outside world onto the opposite side. This form is often referred to as a pinhole camera.
When aided by a lens, the hole in the camera doesn't have to be tiny to create a sharp and distinct image, and the exposure time can be decreased, which allows cameras to be handheld.

Lenses

A photographic lens is usually composed of several lens elements, which combine to reduce the effects of chromatic aberration, coma, spherical aberration, and other aberrations. A simple example is the three-element Cooke triplet, still in use over a century after it was first designed, but many current photographic lenses are much more complex.
Using a smaller aperture can reduce most, but not all aberrations. They can also be reduced dramatically by using an aspheric element, 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 common in photography, but are used in some cases due to their very low weight. The recently developed Fiber-coupled monocentric lens consists of spheres constructed of concentric hemispherical shells of different glasses tied to the focal plane by bundles of optical fibers. Monocentric lenses are also not used in cameras because the technology was just debuted in October 2013 at the Frontiers in Optics Conference in Orlando, Florida.
All lens design is a compromise between numerous factors, including cost. Zoom lenses involve additional compromises and therefore normally do not match the performance of prime lenses.
When a camera lens is focused to project an object some distance away onto the film or detector, the objects that are closer in distance, relative to the distant object, 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. 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.
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.

Aberration

Aberrations are the blurring and distorting properties of an optical system. A high quality lens will produce a smaller amount of aberrations.
Spherical aberration occurs due to the increased refraction of light rays that occurs when rays strike a lens, or a reflection of light rays that occurs when rays strike a mirror near its edge in comparison with those that strike nearer the center. This is dependent on the focal length of a spherical lens and the distance from its center. It is compensated by designing a multi-lens system or by using an aspheric lens.
Chromatic aberration is caused by a lens having a different refractive index for different wavelengths of light and the dependence of the optical properties on color. Blue light will generally bend more than red light. There are higher order chromatic aberrations, such as the dependence of magnification on color. Chromatic aberration is compensated by using a lens made out of materials carefully designed to cancel out chromatic aberrations.
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.

Focus

is the tendency for light rays to reach the same place on the image sensor or film, independent of where they pass through the lens. For clear pictures, the focus is adjusted for distance, because at a different object distance the rays reach different parts of the lens with different angles. In modern photography, focusing is often accomplished automatically.
The autofocus system in modern SLRs use a sensor in the mirrorbox to measure contrast. The sensor's signal is analyzed by an application-specific integrated circuit, and the ASIC tries to maximize the contrast pattern by moving lens elements. The ASICs in modern cameras also have special algorithms for predicting motion, and other advanced features.

Diffraction limit

Since light propagates as waves, the patterns it produces on the film are subject to the wave phenomenon known as diffraction, which limits the image resolution to features on the order of several times the wavelength of light. Diffraction is the main effect limiting the sharpness of optical images from lenses that are stopped down to small apertures, while aberrations are the limiting effect at large apertures. 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.
The diffraction-limited optical spot size on the CCD or film is proportional to the f-number, making the overall detail in a photograph proportional to the size of the film, or CCD divided by the f-number. For a 35 mm camera with, this limit corresponds to about 6,000 resolution elements across the width of the film = 6,500.
The finite spot size caused by diffraction can also be expressed as a criterion for distinguishing distant objects: two distant point sources can only produce separate images on the film or sensor if their angular separation exceeds the wavelength of light divided by the width of the open aperture of the camera lens.

Chemical processes

Gelatin silver

The gelatin silver process is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography rarely rely on any other chemical process to record an image.

Daguerreotypes

Daguerreotype was the first publicly available photographic process; it was widely used during the 1840s and 1850s. "Daguerreotype" also refers to an image created through this process.

Collodion process and the ambrotype

The collodion process is an early photographic process. The collodion process, mostly synonymous with the "collodion wet plate process", requires the photographic material to be coated, sensitized, exposed and developed within the span of about fifteen minutes, necessitating a portable darkroom for use in the field. Collodion is normally used in its wet form, but can also be used in dry form, at the cost of greatly increased exposure time. The latter made the dry form unsuitable for the usual portraiture work of most professional photographers of the 19th century. The use of the dry form was therefore mostly confined to landscape photography and other special applications where minutes-long exposure times were tolerable.

Cyanotypes

Cyanotype is a photographic printing process that produces a cyan-blue print. Engineers used the process well into the 20th century as a simple and low-cost process to produce copies of drawings, referred to as blueprints. The process uses two chemicals: ferric ammonium citrate and potassium ferricyanide.

Platinum and palladium processes

Platinum prints, also called platinotypes, are photographic prints made by a monochrome printing process involving platinum.

Gum bichromate

Gum bichromate is a 19th-century photographic printing process based on the light sensitivity of dichromates. It is capable of rendering painterly images from photographic negatives. Gum printing is traditionally a multi-layered printing process, but satisfactory results may be obtained from a single pass. Any color can be used for gum printing, so natural-color photographs are also possible by using this technique in layers.

C-prints and color film

A chromogenic print, also known as a C-print or C-type print, a silver halide print, or a dye coupler print, is a photographic print made from a color negative, transparency or digital image, and developed using a chromogenic process. They are composed of three layers of gelatin, each containing an emulsion of silver halide, which is used as a light-sensitive material, and a different dye coupler of subtractive color which together, when developed, form a full-color image.

Digital sensors

An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves into signals, small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, camera phones, optical mouse devices, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, electronic and digital imaging tends to replace chemical and analog imaging.