Optical Measuring Instruments

There are many types of optical instruments. The one common feature of these instruments is that they measure a property of light. Optical instruments can be used to measure distances, identify unknown compounds and help diagnose vision problems. This is because light changes in different environments and these changes can be measured using optical instruments.

Photometer

• Photometer is used to measure the light intensity of an unknown source. The light intensity of the unknown source is compared to a known source or standard light source. The first photometer was developed in the 1800s and the standard source used was a candle made from whale oil. The photo meter uses the inverse square law to calculate the light intensity. This states that the intensity of the light at a specific distance relates to the intensity of light from the standard light source at the same distance.

Autocollimator

• The autocollimator is used to measure very small angles. This optical instrument has very high sensitivity and is used to detect angular movement, precision alignment, angular monitoring over time and verification of standard angles. There are both digital and visual autocollimators available. Digital versions contain an electronic photo detector that measures the angle from a reflected beam of light. A visual autocollimator relies on its operator's eye to function as the photo detector. Digital models are more precise, as the readings from a visual model differ depending on the operator.

Refractometer

• A refractometer measures how much light will bend as it moves from air into a sample. This refractive index is used to identify a liquid sample by comparing it to known refractive indexes to determine the sample's purity, and to determine the concentration of a solution by comparing the refractive index to a standard curve. The refractometer works on the theory that as light moves through different substances, its speed changes. Therefore, when light speed changes, the direction that the light moves also changes.

Vertometer

• A vertometer measures the power of glass lenses and contact lenses. Other names for a vertometer are focimeter or lensmeter. The lens is clamped into place and then a graticule, or grid pattern, is viewed through the lens. The target on the graticule contains several parallel lines and a single line that is perpendicular to the parallel lines. The power dial is turned until the target on the graticule is focused. This is a more accurate way to measure lens power than hand neutralization, a simpler technique.

Interferometer

• An interferometer measures the interference between two different light sources. This type of optical instrument is used to measure images and distances in space, as it can produce very accurate distance measurements. The machine works by splitting a beam of light. The two resulting beams heat two mirrors, one fixed and one moveable. The reflected beams are then combined again, resulting in an interference pattern.