The natural accommodation of the human eye to different distances results in focus cues, which contribute to depth perception and appearance. Since focus cues are very difficult to reproduce in an electronic display, it is desirable to know how much they contribute to realistic image appearance. In this work we quantify the potential benefit of focus cues in terms of increased realism compared to regular stereo image presentation. As a secondary goal, we evaluate whether three depth-of-field rendering techniques, which reproduce defocus blur at three different degrees of accuracy, can reintroduce the benefits of focus cues. Our findings confirm the importance of focus cues for realistic image appearance, and also show that they cannot easily be substituted by depth-of-field rendering.