Software configurable optical test system for refractive optics

Abstract

SCOTS (software configurable optical test system) is a useful tool that can provide lens manufacturers with the ability to evaluate the net performance of a lens system without the use of complex metrology systems and setups. This technique is based on measuring the transverse ray aberrations of rays to obtain wavefront information using transmission deflectometry, the refractive equivalent of reflection deflectometry. Some work using deflectometry on refractive surfaces has been briefly reported in the past, where the power of a single lens has been the measurement objective. Results showing the use of deflectometry on reflective optical surfaces, such as the primary mirror of the Giant Magellan Telescope (GMT) show that this method has a large dynamic range in which measurement accuracy is comparable with those of interferometric methods; generating interest on our part, to investigate deflectometry for refractive systems in more detail. In this paper, we focus on reporting initial tests using SCOTS by measuring simple refractive elements, such as 1 diameter biconvex BK7 lenses. Results indicate a good agreement when comparing them with equivalent MATLAB/ZEMAX wavefront measuring models, which include the measured lens parameters, where the estimated and measured wavefront RMS values and spherical aberration Zernike coefficient agree on average to within 10nm. We also investigate the effect of the chromatic aberration on the refractive optical system by collecting data using three different wavelengths: 620nm, 550nm and 450nm. The alignment of the test setup was done rapidly and we used an LCD screen with a pixel pitch of 0.1905mm. The camera used for the measurements was a simple digital CCD camera.