Densitometers measure optical density and are used in scientific applications, photography, and printing. They use transmission or reflection techniques and can measure bone density through X-rays. Calibration is necessary for accuracy.
A densitometer is scientific equipment designed to measure optical density. Densitometers are used in a variety of scientific applications and also by photographers and printers who need to verify the quality of their work. A number of companies manufacture densitometers, including special equipment customized for particular applications.
Some densitometers use a transmission technique, in which light is transmitted through the substance to be measured, and a photoelectric cell reads the light as it passes through it. Optical density is determined by observing how much light has passed through the object being read. This type of densitometer is often used to measure the optical density in film, with the data used in a variety of ways during the film development process.
A reflection process can be used with solid objects that cannot be used with a transmission densitometer. In this case, the amount of light reflected by the object is measured. For example, a photographer might use the transmission method to read film and the reflection method to read a developed photograph. Some densitometers are capable of both functions, allowing people to adjust the setting for various uses.
Printers can use densitometers to check color saturation and to confirm that a print run is consistent. The densitometer is also used during print checks to confirm that the material is printing correctly and to compare the appearance of the films used to prepare the printing plates with the resulting printed product.
Densitometry is used in a wide variety of ways. In a special type of densitometry used to measure bone density, density is measured by passing X-rays through the body. In this case, bone density can be determined by looking at how many X-rays pass through. Extreme variations in bone density can often be identified simply by looking at x-ray film, as more porous bone will appear darker on x-ray, while denser bone will appear whiter, indicating that those areas of the film were not as heavily exposed to X-rays.
Densitometers usually need to be warmed up before they can be used. It’s also important to calibrate them to ensure that the readings are accurate and consistent. Calibration can be performed with manufacturer supplied calibration cards; each card has a number of density sample areas that can be analyzed through the densitometer, comparing the device’s readings to the density level printed on the card.
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