Have you ever used one of those old-school camera calibration charts to test the resolution of your lenses? Did you know they’re called Tri-bar Arrays? For years they were the standard test of a lens’ ability to resolve fine details. The standard was created by the American military back in the 1950s, and the Tri-bar Array remained the de facto standard until the digital era brought it to an end in the mid 2000s. Because of the pattern’s military origins, there are still some intriguing large-scale remnants of the pattern in use today. You see, various air bases and military installations around the country painted giant versions of the Tri-Bar Array adjacent to runways for use as a calibration and testing tool for aerial and satellite cameras and lenses. It’s a pretty neat holdover from the cold war days, and thanks to Google earth we can see these interesting artifacts for ourselves. Thanks to Michael Johnston of The Online Photographer for pointing us to this interesting article at the Center for Land Use Interpretation.