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Technical Photography

imaging image ray infrared

TED KINSMAN
Kinsman Physics Productions

Technical photography is a broad description that embraces a very wide range of techniques, applications, disciplines, and industries. The individual topics are dealt with in more detail under their specific headings. Here we attempt to give a broad overview.

This specialty involves the production of images created with the ultimate goal of being analyzed for their information content or for measurement purposes. The informational content in the image may relate to all four dimensions, and thus can include any combination of motion, location, position and size, and their changes with time and environment. The wavelength of the recorded radiation is another variable. Of course not all of technical photography deals with all these parameters and many such images simply record an experiment, equipment, situation, or phenomenon. The information contained in the image may be qualitative, quantitative, or educational in nature. In many instances the role of technical photography is to solve or document industrial or manufacturing problems. Given this variety, the technical photographer must know why an image is needed, who will be using it, and for what purposes. The resulting images are not usually intended to have aesthetic value, but it is not excluded.

Some photographic techniques that fall into this area are infrared, high-speed flash, ultraviolet, streak, schlieren, medical, forensics, thermal, and radiography (X-ray). In many instances several of these techniques can be combined to solve unique or challenging imaging problems. For example, high-speed flash radiography is used to study the interaction
of gun powder, shell casing, and bullet within a firearm at the moment when the gun powder ignites.

High-speed flash work is characterized as requiring a short duration of electronic flash or pulsed light source with a time of 1/10,000 of a second or less. In the case of the pulsed-light system, the role of the camera shutter to control the light for the camera is changed and the duration of the light pulse becomes the shutter. The role and versatility of high-speed flash imaging continues to progress in parallel with laser technology. This form of technical photography is quite common in industry as it is used to diagnose and research events such as machine actions or processes that happen at rates faster than the eye can resolve. Recently, this technique has been combined with robotic vision systems to prevent blur in digital images and allow optical recognition techniques to identify flaws in products. An example of such an application would be for identification of empty bottles on a bottle filling system used in the soft drink industry.

Infrared photography once involved bulky electronic cameras and specialized film. With the use of contemporary infrared imaging systems and far-infrared transparent materials in optical components, it has expanded to image heat radiation at a wavelength of 13 >m and beyond, a wavelength ten times longer then film could detect. This is the so-called thermal infrared, and commercial imaging systems of this type are known as microbolometers. The microbolometer uses solid-state pixelated detectors like a charge-coupled device (CCD), but is able to detect heat radiation. This form of imaging is used in many industrial applications to detect overheating in electronics and heat loss in homes, and has recently been used in medicine to observe abnormal blood flows. Infrared imaging has long been used in security applications as it can yield an image without the use of visible light. Recent applications of this imaging technology are found in the evaluation of airplane passengers with elevated body temperatures indicating possibly contagious infections (e.g., SARS), or the imaging of cattle before processing to quickly gauge body mass not visible behind the tangle of the animal’s coat.

Streak photography is a technique where the sensor or film travels along with an image of the object that is to be recorded. This technique dates back to the turn of the 20th century and is often described as “photofinish” photography and has long been used, particularly in horse racing. Modern use of this imaging technique is sometimes combined with ultrasound technologies where a baby’s heart can be imaged in utero as a sine wave. The frequency of the sine wave related to the beating of the heart shares its structural information not observable in any other way.

Schlieren photography is a technique that uses a special optical system to measure changes in the refractive index of a transparent medium that is contained within or surrounds the subject in question. This technique is commonly used to observe and measure the differences in air density when evaluating aerodynamic models in wind tunnels.

Forensic photography is a specialized form of photography where evidence, or other relevant subjects that are important to a crime, including the locations of objects, are photographed in a standardized approach. The resulting images can then be analyzed as appropriate for future presentation in a court of law. All forensic images collected must contain all relevant information including dimensional scales. In forensic photography, image processing can result in photographic information being compromised, and the integrity of the picture being challenged, so the preservation of the chain of evidence is important.

Radiography or X-ray imaging is commonly used in medicine, industry, and security work. Although the medical use of X-ray imaging is well documented, the industrial use of X-rays and radioactive sources to detect and certify metal welding is its largest use. Recent advances in computer imaging make applications like CT scans a common diagnostic medical procedure to evaluate soft tissue where traditional X ray imaging is challenged to differentiate structure. Other advances in digital X-ray detectors such as backscattered X-ray systems allow security inspectors to look for concealed weapons under clothing and inside luggage and complete vehicles.

As in all of technical photography, the role of X-ray imaging continues to grow as detectors gain sensitivity, decrease in cost, and use advanced imaging and image analysis techniques.

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