This invention relates to an infra red wavefront sensor device (10) including: • a plurality of tapered coherent fibre optic image conduits (12a, 12b), wherein each image conduit has an input surface (14a, 14b) and a body portion (16a, 16b) that tapers to an output surface (18a, 18b) and is configured to transmit an infra-red image incident on the input surface (14a, 14b) to the output surface (18a, 18b), in which the input surfaces (14a, 14b) are substantially coplanar thereby defining an image plane； • a plurality of detector arrays (26), wherein each detector array has a plurality of detector cells which are responsive to infra-red radiation, and in which each detector array (26) is positioned so as to detect an infra-red image appearing at the output surface (18a, 18b) of the paired image conduit (12a, 12b) by producing an output signal； and • an image processor (28) responsive to the output signals of the detector arrays (26) and configured to combine said output signals to produce a composite image.
