Within the area of broadcasting and entertainment, stereoscopic displays are used to heighten the viewer's sense of excitement and quality. To evaluate these subjective experiences, an appreciation-oriented approach seems to be appropriate. Within this framework, this paper reports on two experiments in which we investigated the influence of image disparity, convergence distance and focus length on the subjective assessment of depth, naturalness, quality and eye-strain. Twelve observers with normal or corrected-to-normal vision and good stereopsis viewed a fully randomized presentation of stereoscopic still images that varied systematically in image disparity, convergence distance and focus length. In the first experiment observers were asked to rate, in separate counterbalanced sessions, their impression of depth, naturalness of depth and quality of depth. In the second experiment observers were asked to rate the eye-strain they experienced on a five point rating scale. Results indicate that observers prefer a stereoscopic presentation of images over a monoscopic presentation. A clear optimum for quality and naturalness judgments was found at 4 cm image disparity, which was also rated by observers as the stereoscopic condition that produced the least eye-strain. Extreme image disparities were found to be annoying, producing low quality and naturalness ratings accordingly. Although there was a strong linear relationship between naturalness and quality (a correlation of r equals 0.96), a small but systematic shift could be observed. This quality-naturalness shift is discussed in relation to similar, yet more pronounced findings in the color domain.