A 50 MHz C-scan imaging system is used to find defects in ceramics. The imaging system consists of a microcomputer-controlled scanner for data acquisition and signal conditioning. Synthetic aperture imaging at 50 MHz is carried out to obtain 3-D images of flaws. Image reconstruction is accomplished digitally on a minicomputer. A square synthetic aperture is used to image flaws in flat disc samples and a cylindrical synthetic aperture is used in the cylindrical rod case. We have developed the theory to predict the imaging performance of the two aperture geometries. The respective point spread functions are simulated and agree well with theoretical results. Special attention is given to reconstructing images of specular reflectors. Computer simulations based on theoretical flaw models have been carried out.