Camera Lens

Background

The camera lens is an invention that attempts to duplicate the operation of the human eye. Just like the eye, the lens sees an image, focuses it, and transmits its colors, sharpness, and brightness through the camera to the photographic film, which, like our memory, records the image for processing and future use. Lenses are made of optical glass or plastic. They focus light rays by refracting or bending them so that they meet or converge at a common point.

A simple lens "sees" well through its center, but its vision around the edges tends to blur. Blurring, color changes, distortion of lines, and color halos around objects are caused by defects in the lens called aberrations. Some aberrations can be corrected in the simple lens by shaping one or both surfaces so they are aspheric; aspheric curves vary like the curves of a parabola, rather than staying constant like the curvature of a sphere. A camera lens reduces the effects of aberrations by replacing a simple lens with a group of lenses called lens elements, which are lenses of different shapes and distances of separation. The lens becomes more complex as greater correction of vision is achieved. The lens will also be more complex depending on the size of the aperture—the opening that allows light to pass through—and the range of angles it "sees." Lens design used to rely on the optician's art and considerable experimentation. Today, computer programs can adjust the shaping and spacing of lens elements, determine their effects on each other, and evaluate costs of lens production.

Lens elements are usually described by their shape. The convex lens curves outward; a biconvex lens curves outward on both sides, and a plano-convex lens is flat on one side and outwardly curved on the other. There are also concave lenes, biconcave, and plano-concave lenses. The elements are not necessarily symmetrical and can curve more on one side than the other. Thickening the middle of the lens relative to its edges causes light rays to converge or focus. Lenses with thick edges and thin middles make light rays disperse. A complex camera lens contains a number of elements specially grouped. The combination of the composition, shape, and grouping of the elements maximizes the light-bending properties of the individual elements to produce the desired image. The lens is focused by moving it nearer or farther from the film or focal plane. The lens can be twisted, causing the lens elements to move in and out along a spiral screw thread machined into the casing of the lens. Twisting the lens also moves a scale on the casing that shows the distance of the best focus.

The stop or diaphragm is a specialized part of the lens. In simple cameras, the stop is a fixed stop or a ring of black sheet metal that is permanently set in front of the lens. Box cameras, studio cameras, and some cameras of European manufacture use a sliding stop, which is a strip of metal that slides across the front of the lens between grooves. It has two or more holes of different sizes that are the apertures. Lenses with a variable stop have a machined ring on the outside of the lens mount, printed with f-stop numbers. By turning this ring, the diaphragm can be opened or closed. This iris diaphragm works much like the iris of the eye in allowing adjustments for varied light conditions.

The lens in a compact camera is usually a general-purpose lens with a normnal focal length that takes pictures of an image the way our eyes see it. Lenses designed for special purposes are used with more advanced cameras. Telephoto lenses work much like binoculars or telescopes, and make a distant image appear closer. Wide-angle lenses make the image appear farther away; a panoramic lens is a special kind of wide-angle lens that is useful for taking pictures of broad expanses of scenery. Some disposable cameras are equipped with panoramic lenses. A fish-eye lens is also a special kind of wide-angle lens that deliberately distorts the image so the central part is enlarged and the outer image details are compressed. Fish-eye lenses cover very wide angles like horizon-to-horizon views. Another special purpose lens is the variable-focus lens, also called a "zoom" lens. It uses moveable lens elements to adjust the focal length to zoom closer to or farther away from the subject. These lenses are complex and may contain 12 to 20 lens elements; however, one variable-focus lens may replace several other lenses. Some compact cameras also have limited zoom, telephoto, or wide-angle features. The single-lens reflex (SLR) camera is made so that the photographer sees the same view as the lens through the viewfinder. This enables the photographer to plan the image that will appear on film with the flexibility of a variety of interchangeable lenses.

History

The camera lens evolved from optical lenses developed for other purposes, and matured with the camera and photographic film. In 1568, a Venetian nobleman, Daniel Barbaro, placed a lens over the hole in a camera box and studied sharpness of image and focus. His first lens was from an old man's convex spectacles. The astronomer Johann Kepler elaborated on Barbaro's experiments in 1611 by describing single and compound lenses, explaining image reversal, and enlarging images by grouping convex and concave lenses.

In the 1800s, the first box cameras had a lens mounted in the opening in the box. The lens inverted the image on a light-sensitive plate at the back of the box. There was no shutter to open the lens; instead, a lens cap was removed for several seconds or longer to expose the plate. Improvements in the sensitivity of the plate necessitated ways of controlling the exposure. Masks with different sized openings were made for insertion near the lens. The iris diaphragm was also developed to control the aperture. Its metal leaves open and close together to form a circular opening that can be varied in diameter.

In 1841, Joseph Petzval of Vienna designed a portrait lens with a fast aperture. Previously, lenses made for daguerreotype cameras were best suited for landscape photography. Petzval's lens allowed portraits to be taken ten times faster, and the photograph was less likely to be blurred. In 1902, Paul Rudolph developed the Zeiss Tessar lens, considered the most popular ever created. In 1918, he produced the Plasmat lens, which may be the finest camera lens ever made. Rudolph was followed shortly by Max Berek, who designed sharp, fast lenses that were ideal for miniature cameras.

Other essential developments in lens history include lens coating technology, use of rare-earth glass, and calculation methods made possible by the computer. Katharine B. Blodgett developed techniques for thin-coating lenses with soap film to remove reflection and improve light transmission in 1939. C. Hawley Cartwright continued Blodgett's work by using coatings of metallic fluorides, including evaporated magnesium and calcium that were four-one-millionths of an inch thick.

Design

Design of a camera lens begins by identifying the photographer who will use it. When the market is identified, the lens designer selects the optical and mechanical materials, the optical design, the appropriate method for making the mechanical parts, and, for auto focus lenses, the type of inter-face between the lens and camera. There are conventions or patterns for the different categories of lenses, including macro, wide-angle, and telephoto lenses, so some design aspects are standardized. Advancements in materials give designers many challenging options, however. In selecting materials, the engineer must consider a range of metals for the components and various types of glasses and plastics for the lenses, all the while mindful of the final cost to the photographer.

When the designer has completed the design, its performance is tested by computer simulation. Computer programs that are specific to lens manufacturers tell the designer what kind of image or picture the lens will produce at the center of the image and at its edges for the range of lens operation. Assuming the lens passes the computer simulation test, the criteria for performance that were chosen initially are reviewed again to confirm that the lens meets the needs identified. A prototype is manufactured to test actual performance. The lens is tested under varying temperature and environmental conditions, at every aperture position, and at every focal length for zoom lenses. Target charts in a laboratory are photographed, as are field conditions of varying light and shadow. Some lenses are aged rapidly in laboratory tests to check their durability.

Additional design work is needed if the lens focuses automatically, because the auto focus (AF) module must work with a range of camera bodies. The AF module requires both software and mechanical design. Extensive prototype testing is performed on these lenses because of their complex functions and because the software is fine-tuned to each lens.

Raw Materials

The raw materials for the lenses themselves, the coating, the barrel, or housing for the camera lens, and lens mounts are described below in the manufacturing section.

The Manufacturing
Process

Grinding and polishing lens elements

• 1 Optical glass is supplied to lens manufacturers by specialized vendors. Usually, it is provided as a "pressed plate" or sliced glass plate from which the elements are cut. The glass elements are shaped to concave or convex forms by a curve generator machine that is a first-step grinder. To reach the specifications for its shape, a lens goes through a sequence of processes in which it is ground by polishing particles in water. The polishing particles become smaller in each step as the lens is refined. Curve generation and subsequent grinding vary in speed depending on the frailty, softness, and oxidation properties of the optical materials.

  After grinding and polishing, the elements are centered so that the outer edge of the lens is perfect in circumference relative to the centerline or optical axis of the lens. Lenses made of plastic or bonded glass and resin are produced by the same processes. Bonded materials are used to make lenses with non-spherical surfaces, and these lenses are called "hybrid aspherics." The aspherical surfaces of these lenses are completed during centering.

Coating lenses

• 2 Formed lenses are coated to protect the material from oxidation, to prevent reflections, and to meet requirements for "designed spectrum transmission" or color balance and rendition. The lens surfaces are carefully cleaned before coating. Techniques for applying coatings and the coatings themselves are major selling points for a manufacturer's lenses and are carefully guarded secrets. Some types of coatings include metal oxides, light-alloy fluorides, and layers of quartz that are applied to lenses and mirrors by a vacuum process. Several layers of coating may be applied for the best color and light transmission, but excessive coating can reduce the light that passes through the lens and limit its usefulness.

Producing the barrel

• 3 The barrel includes the chassis that supports the various lens elements and the cosmetic exterior. Metal mounts, grooves, and moving portions of the lens are critical to the performance of the lens, and are machined to very specific tolerances. Lens mounts may be made of brass, aluminum, or plastic. Most metal barrel components are die-cast and machined. Metal mounts last longer, maintain their dimensions, can be machined more precisely, and can be dismantled to replace elements, if necessary. Plastic mounts are less expensive and of lighter weight. If the barrel is made of engineering plastic, it is produced by a highly efficient and precise method of injection molding. The interior surfaces of the barrel are also coated to protect them and to prevent internal reflection and flare.

Assembling the lens

• 4 Other parts of the lens, such as the diaphragm and auto focus module, are produced as subassemblies. The iris diaphragm is constructed of curved leaves cut out of thin sheets of metal. The metal leaves are held in place by two plates. One plate is fixed, the other moves, and has slots for sliding pins. These slide the leaves back toward the barrel to open the diaphragm or into the center to close the opening as the f-stop ring is turned. The diaphragm assembly is fastened into place when the lens mount is attached to the end of the barrel. The auto focus is also added, the optical elements are positioned, and the lens is sealed. After final assembly, the lens is adjusted and inspected rigorously. It must meet the design standards for optical resolution, mechanical function, and auto focus response. Lenses may also be tested by subjecting them to shocks, dropping, and vibration.

Quality Control

Approaches to lens manufacture vary greatly among companies. Some use full automation including industrial robot s to make their products, others use large assembly lines, and still others pride themselves on hand-crafting. Quality and precision are essential to lens production, however, regardless of manufacturing approach. Incoming materials and components are rigorously inspected for quality and compliance with engineering specifications. Automated processes are also inspected constantly and subjected to tolerance checks. Hand-craftsmanship is performed only by skilled artisans with long years of training. Quality control and stress tests are incorporated in each manufacturing step, and elements and components are measured with precise instruments. Some measuring devices are laser-controlled and can detect deviations of less than 0.0001-millimeter in a lens surface or in lens centering.

The Future

Camera lenses are enjoying new developments in many areas. The consumer's interest in the best photos for the lowest cost has led to disposable cameras with simple but effective lenses. Lenses for professional photographers and for specialized uses such as high-performance binoculars or telescopes are made with exotic and "non-preferred" glasses that are more sensitive, expensive, and harder to obtain than traditional materials. These are called "abnormal dispersion" materials because they merge all the colors in the light passing through the lens to produce the best images, rather than allowing colors to disperse like a simple lens. Water and other liquids also bend light, and scientists have identified liquids that are abnormally dispersive and can be trapped between layers of ordinary glass to produce the same image quality as exotic optical glass. The ordinary or "preferred" glass (preferred because of low cost and workability) is bonded around the liquid with flexible silicone adhesive. The resulting "liquid lens" may replace several elements in a professional-quality lens. It also reduces the coating required and the amount of lens polishing needed because the liquid fills imperfections in the glass. The cost of the lens is reduced, and the light transmission properties are improved. Lens makers in the U.S., Japan, and Europe are preparing to produce liquid lenses in the near future.

Where To Learn More

Books

Bailey, Adrian and Adrian Holloway. The Book Of Color Photography. Alfred A. Knopf, 1979.

Collins, Douglas. The Story of Kodak. Harry N. Abrams, Inc., Publishers, 1990.

Sussman, Aaron. The Amateur Photographer's Handbook. Thomas Y. Crowell Company, 1973.

Periodicals

Coy, Peter, ed. "A Clear-Eyed View from Liquid Camera Lenses." Business Week, January 17, 1994, p. 81.

From Glass Plates to Digital Images. Eastman Kodak Company, 1994.

"Photographic Lenses." Photographic, April 1991, pp. 56-57.

"Liquid Lens." Popular Science, May 1994, p. 36.

—Gillian S. Holmes

Camera

Background

Photography has staked its claim as America's favorite hobby, and today, cameras are available in sizes and shapes to suit the needs of every kind of photographer and budget. Much like Henry Ford wanted a Model T in every driveway, George Eastman thought every consumer should be able to afford a camera. His developments in photographic film and portable, affordable cameras led to photo negatives from which prints can be made, color film, color positives or slides, pocket-sized cameras, and point-and-shoot cameras (including single-use or disposable cameras) known for their ease of operation. Photography has also branched into more complex directions with developments in the camera lens, the single-lens reflex (SLR) camera that allows the photographer to see through the viewfinder what the camera sees, state-of-the-art electronics, and an assortment of mechanical controls.

From the simplest amateur camera to the most complex, professional piece of equipment, all cameras have five common parts. The lens is made of glass or plastic (or groups of glass elements) and focuses light passing through it on the film to reproduce an image. The diaphragm is an opening or aperture that controls the amount of light entering the camera from the lens and so limits the film's exposure to light. The diaphragm ranges in complexity from a fixed lens, opening in a simple camera, to apertures that can be adjusted manually or automatically.

The three remaining parts common to all cameras are incorporated in the camera body (also called a chassis or housing). The shutter also limits the film's exposure to light by controlling the length of time the film is exposed. Shutter speed can be adjusted in many cameras to suit light conditions and the photographic subject matter; moving objects can be frozen on film with fast shutter speeds. The camera body encloses and protects the operating parts of the camera, including a light meter, the film transport system, built-in flash, the reflex viewing system, and electronic and mechanical components. The body must be lightproof, durable, and resistant to environmental changes. The viewfinder is a specialized lens the photographer uses to preview the photograph either through the lens, if the camera is a reflex-type, or in a separate view for simpler cameras.

History

The story of the camera may have begun thousands of years ago when people first noticed that a chink in a wall or hole in a tent let light into the room and made a colored, upside-down reflection. The word camera means room, and the first camera was a room (or tent, actually) called a camera obscura with an eye at the top of the tent much like a periscope that could be rotated. Artists used it by training the eye on an image, which was reflected down onto the artist's work table where it could be drawn. Euclid and Aristotle studied the principles of light, and Leonardo da Vinci described and diagrammed the camera obscura, although it was not his discovery.

The first portable cameras were boxes with lenses on the front over apertures and plates at the back. The plates were flat and covered with light-sensitive materials. By removing the cover over the lens, light entered the box and was focused by the lens on the rear plate. Early exposures took from several seconds to a number of minutes because the sensitivity of the plates was so poor. Also, the only image was the one on the plate; photos, like those produced by Louis Daguerre and Joseph Niepce in France during the 1820s and 1830s, were unique artworks that were not reproducible. Plate-type photography continued to be refined, and, as plates were made more sensitive to light, the lens was improved to provide a variable aperture to control light exposure. The camera was also modified by adding a shutter, so exposure time could be limited to seconds or less. The shutter was made of several metal leaves that opened or closed completely. A rubber bulb was used to provide air pressure to operate the shutter.

The invention of roll film in 1889 by George Eastman made photography more portable because cameras (and their operators) did not need to carry cumbersome plates and chemicals. Eastman's invention and the cameras he also manufactured made photography a popular hobby. By 1896, the Eastman Kodak Company had sold 100,000 cameras. The camera was modified to include a film transport system with take-up spools, a winder, a lever for cocking the shutter, and shutter blinds. By the turn of the century, the major obstacles to taking photographs had been eliminated and, in the twentieth century, photographic history has branched from the basic concept and perfected each development. These developments are numerous, but include design and perfection of flash units including synchronized and high-speed flash; continued miniaturization of cameras; the Polaroid system of producing a finished print in the camera and without a negative; design of high quality equipment like Leica, Zeiss, and Hasselblad cameras and lenses; and advocacy of photography as an art form by photographers such as Matthew B. Brady, Alfred Stieglitz, Edward J. Steichen, and Ansel Adams.

George Eastman introduced his Kodak™ camera in 1888 and revolutionized popular photography. The Kodak camera was small, handheld, inexpensive, and, for the first time, made especially to hold a roll of flexible film. Prior to this, light sensitive chemicals captured the black-andwhite negative images on pieces of glass. Large cameras were used to hold the photographic plates and a tripod was needed for support. For ordinary Americans, photography consisted of posed portraits in a professional photographer's studio. The Kodak camera allowed the average person to take photographs of their families, their homes, and their surroundings. It inaugurated the snapshot era of do-it-yourself photography. Awarded a medal at the Photographers' Annual Convention as the photographic invention of 1888, thousands of $25.00 Kodak cameras sold during the first year.

By 1889, celluloid, a type of plastic, replaced the paper of the first flexible film base. Another unique feature for the time was that the amateur photographer returned the unopened camera to the Rochester, New York, factory. There the film negatives were processed and the 2.5 in (6.35 cm) circular images were printed on paper and mounted on cardboard. The camera was then re-loaded with an unexposed roll of flexible film and returned to the customer with the processed photographs and negatives. This cost $10.00 and produced 100 snapshots. This activity became so popular that the term kodaking soon meant a fun outing to take snapshots.

Cynthia Read-Miller

Design

Camera design is an intricate and specialized field. All designs begin with conceptualizing a product and evaluating the potential market and the needs of the consumer for the proposed product. Designs begin at computer-aided design (CAD) work stations, where the product's configuration and workings are drawn. The designer selects the materials, mechanics, electronics, and other features of design and construction, including interfaces with lenses, flash units, and other accessories.

The computer design is also tested by computer simulation. Designs that pass the computer program's review are checked against the initial concept and marketing and performance goals. The camera may then be approved for production as a prototype. Manufacture of a prototype is needed to test actual performance and to prepare for mass production. The prototype is tested by a rigorous series of field and laboratory tests. Prototypes selected for manufacture are used by the engineers to prepare design details, specifications, and toolmaking and manufacturing processes. Many of these are adapted directly from the CAD designs by computer-aided manufacturing (CAM) systems. Additional design is needed for any systems or accessories that interface with the new product. Camera manufacturers can conceive a new product and have it ready for shipment in approximately a year by using CAD/CAM design methods.

The Manufacturing
Process

Camera chassis and cover

• 1 The camera chassis or body and back cover are made of a polycarbonate compound, containing 10-20% glass fiber. This material is very durable, lightweight, and shock-resistant as well as tolerant to humidity and temperature changes. Its major disadvantage is that it is not resistant to chemicals. The polycarbonate is molded to very specific tolerances because the internal workings of the camera must fit precisely to work well and to use the strength of the chassis for protection against jarring and other shocks, to which mechanical and electronic parts are sensitive. After the chassis is molded and assembled, it becomes the frame to which other parts of the camera, like electrical connections in the battery housing and the auto focus module, are attached.

Shutter and film transport system

• 2 The shutter assembly and film transport system are manufactured on a separate assembly line. These parts are largely mechanical although the film transport system has electronics to read the speed of the film. DX film coding appears as silver bands on the roll of film, and these are detected by multiple contacts in the film chamber. More advanced cameras have microchips that see the data imprinted in the silver bands and adjust shutter speed, flash, and other camera actions. Again, all parts are precisely made; the film magazine size must be accurate to 60 thousandths of an inch.
• 3 The shutter functions like a curtain that opens and closes. It must operate exactly to expose the film for the correct length of time and to coordinate with other operations such as the flash. The shutter is made of different materials depending on the type of camera and manufacturer.

Viewfinder lens

• 4 The viewfinder lens is a specialized lens that is manufactured using the same methods as a camera lens. The viewfinder also is made of optical glass, plastic, or glass/plastic combinations. All but the simplest viewfinders contain reticles that illuminate a frame and other information on the eyelens to help the photographer frame the picture. An in-line mirror has specialized coatings for color splitting; as many as 17 coatings may be added to the mirror to correct and modify its reflective properties.

  Single-lens reflex (SLR) cameras have through-the-lens viewing capabilities and are also called real image viewfinders because they let the photographer see as the lens sees. The SLR viewfinder uses a prism to bend the light from the lens to the photographer's eye, and the prism is made of optical glass to precise requirements to make the correct view possible.

LCD screen and electronics

• 5 Advanced cameras and most compact models include a liquid crystal display (LCD) screen that provides information to the photographer such as film speed, aperture, photographic mode (including landscape, portrait, close-up, and other modes), count of photos taken, operation of redeye and flash and other accessories, battery condition, and other data regarding the camera's workings. Integrated circuitry is constructed as subassemblies for the electronic brains of the camera and attached flash, if any.

Quality Control

Quality assurance and quality control practices are a matter of course among camera manufacturers. All departments from manufacturing to shipping have their own quality assurance procedures, and companywide quality assurance is also overseen by a separate division or department. The overseeing quality assurance divisions use statistical methods to monitor aspects of product quality such as camera function, performance, consistency, and precision. They also guide the flow of one assembly system into another and provide corrective measures if problems arise.

Byproducts/Waste

No byproducts result from camera manufacture, but a number of wastes are produced. The wastes include resins, oils such as cutting oil, solvents used for cleaning parts, and metals including iron, aluminum, and brass. The metals and resins are remainders or cuttings from manufactured parts and powder-fine cuttings and dust. The wastes are sorted by type and recovered; they are recycled or treated as industrial wastes by firms specializing in these activities. Camera manufacturers are well aware of the hazards associated with their processes and are careful to observe environmental regulations and sensitivities both in the country of manufacture and in receiving marketplaces. Japan's camera industry stopped using chlorofluorocarbons and trichloroethanes to clean printed circuit boards and camera lenses in 1993 on instruction of Japan's Ministry of International Trade and Industry (MITI), in response to import conditions of other countries, and in acknowledgment of industry-wide respect of the environment.

The Future

For cameras like many other technical products, the future is electronic. The digital still camera introduced in 1995 stores approximately 100 pictures electronically. Instead of a viewfinder or eyepiece, the camera has a color LCD screen similar to the view-type screen on some video cameras, so photos can be viewed instantly. It can be connected by cables to a computer, television, or VCR, so pictures can be transferred to screen, tape, or digitized electronically. The digital camera has another advantage; after taking a photo and reviewing it, the photo can be erased if the photographer does not like the result. There is no wasted film or wasted space in the digital storage process. Also, the photograph can be edited, cropped, or enlarged as it is being taken. After photos have been taken, they remain in the camera as digital files rather than as negatives. To take more photos, these images have to be removed, and they can be stored on a computer disk. All the photos can be moved as a batch, or they can be stored on the computer one-by-one, or deleted from both the camera and computer storage. The transfer process requires software that also allows text to be attached to each picture to date it or write a caption. The camera or computer containing the photos can be hooked up to a video printer to print out copies on paper, or the photos can be transferred to videotape for viewing.

Where to Learn More

Books

Bailey, Adrian, and Adrian Holloway. The Book Of Color Photography. Alfred A. Knopf, 1979.

Collins, Douglas. The Story of Kodak. Harry N. Abrams, Inc., 1990.

Sussman, Aaron. The Amateur Photographer's Handbook. Thomas Y. Crowell Company, 1973.

Periodicals

Antonoff, Michael. "Digital Snapshots from my Vacation." Popular Science, June 1995, pp. 72-76.

From Glass Plates to Digital Images, Eastman Kodak Company, 1994.

—GillianS.Holmes

Cameras

A classical image of a crime or accident investigation involves an investigator photographing the scene. Cameras are vital to forensic science , providing a visual record of the scene. For example, a picture of a blood spatter can be used to help determine the cause of the spill long after the stain itself has been cleaned away.

A visual image is an ideal way to preserve a record of a scene before items are disturbed. Pictures are admissible as legal evidence , providing the prosecution or jury members with an evocative image of the scene. Visual images can aid in reaching a verdict on a crime.

A traditional camera functions by focusing light through a lens onto a surface coated with light-sensitive chemicals. Digital cameras have internal processors that record images in an electronic form, converting wave-like analog information into digital information represented by bits. The concept of the camera dates back to the Renaissance idea of the camera obscura, a small, dark chamber into which light was permitted only through pinholes. During the early nineteenth century, inventors perfected the camera obscura to make the prototype of the modern camera, but early photography was a cumbersome affair characterized by large, boxy cameras and slow exposures.

Surveillance cameras, which have long been an espionage tool, can also be a useful forensic tool. According to the Security Industry Association, by 2003 there were some two million closed-circuit television systems in operation, most of them operated by private businesses for security purposes, in the United States. Many households are also equipped with surveillance cameras.

A forensic investigator can gain legal access to the recordings made by a security camera. This can provide vital information of events before, during, and following the crime or accident.

Increasingly, municipalities are installing surveillance cameras at traffic intersections to monitor the license plate numbers of traffic violators. Such data can be useful forensically.

Virtually all traditional cameras have at least one glass lens, and one with a zoom or telephoto lens typically has three: front and rear convex lenses, with a concave one in between. Though zoom lenses clearly have an application in the world of law enforcement, they can also provide long-distance photos that are useful in a forensic investigation. Miniature and subminiature cameras are usually for photographing images at close range. Typically they would have only a single lens, perhaps with a coating to reduce reflections or glare.

In place of lenses, a pinhole camera uses tiny apertures, or openings, so small that they are known as pinholes. The value of a lens lies in its ability to focus and thus photograph distant objects or ones close by, depending on the settings. By contrast, the value of a pinhole camera is precisely the fact that it does not have lenses, and therefore can produce images of distant and nearby images equally well.

Forensic photography is typically the responsibility of a skilled photographer. The photographer will be careful to photograph the subject from a variety of angles and to use lighting conditions that will emphasize all the detail of the object.

Digital cameras can be useful, since the digitized information can be downloaded to a database for further scrutiny. But, even traditional film photographs can be digitized for electronic storage and analyses.

see also Crime scene investigation; Evidence.