Glossary for Geospatial Science

focal length:  The distance from the lens at which parallel light rays are focused to a point.  Focal length is essentially a measure of the “zoom” level of a camera lens.  Longer focal lengths create a higher zoom level, capture a smaller area of the target scene, and introduce smaller displacement errors.  6-inch, 8.25-inch, and 12-inch focal lengths are common for aerial photography done by government surveying authorities in the United States.   Focal length affects the geometry of the photo and must be provided as an input to computational orthoimage and DEM processes.