An instrument for studying an object (12) comprising a movable
interferometer having a laser source and a plurality of detectors (24)
arranged in an array. The laser source is expanded and arranged to direct
a converging object beam (21) towards a point (22) or line beyond the
object (12) whereby a speckle pattern of light reflected from the object
(12) is detected by the detector or detector array (24). The point (12)
or line at which the laser source is arranged to converge the object beam
(21) is approximately the same distance beyond the object (12) as the
object is spaced from the source. The speed of movement of the
instrument, the sampling rate of the detectors (24) and size of the area
(23) of the object illuminated by the converging laser object beam (21)
are arranged so that sequential areas (23) of the object (12) studied
overlap.