What is a Datum?
Commonly used reference datums and their intended purpose
A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target.
Datum references are critical in optical metrology because it helps establish a coordinate system for assessment of UUT alignment prior to taking a measurement.
- Datum features of an optic are used to define a reference geometry and specify a tolerance (i.e. parallelism, perpendicularity, concentricity) relative to it.
- A datum should be large enough to be physically located for use in measurement of these tolerances.
- Well-defined datum features are related to how the optic is mounted during manufacture and/or final application.
Examples of commonly used datum references for optics are shown below: