1. A detector for measuring sub-pixel pointing jitter comprising: an active coherent light source; an electro-optical sensor including a pixelated sensor array, the electro- optical sensor able to move in three dimensions relative to the light source; a diffuser located on an optical axis extending between the light source and the sensor; the diffuser operative to projects a speckle field on the sensor when the diffuser is illuminated by the light source; the sensor acquires at least a first digital data frame representing a first speckle pattern; a digital processor performing speckle pattern analysis based on speckle blurring or speckle pattern correlation; and, acquired speckle pattern data is analyzed and used to indicate indicative of relative motion between the electro-optical sensor and the light source.