Method of Wave-Front Characterisation in Endoscopic Probes

Abstract

Endoscopic instrumentation is the main means of visualisation and analysis of condition of hardto-reach cavities of different objects in medicine and engineering. The quality of images formed by endoscopic instrumentation is usually limited by geometric aberrations of its optical system. For efficient optical conjugation of endoscopic probes with an eyepiece designed for visual observation and with analytical instruments, detailed information on their aberration characteristics is required. Nowadays, there is no recognised testing methodology for such probes allowing to determine the degree of geometrical aberrations to full extent. In this work, testing was based on analysis of wave-front behind the endoscope eyepiece using a Shack-Hartmann sensor. A bench for registration and analysis of Hartman-nomograms was developed and built for: determining wave-front characteristics in geometrical optics approximation for extra-axis points; evaluation of field curvature and chromatic aberrations; calculation and accounting for measurement errors. The method is exemplified by obtaining wave-front parameters as well as angular and spectral dependences of the defocusing magnitude (characterising field curvature and chromatic aberration of position of an optical system) for a rigid lens endoscope.