Light field rendering (LFR) is an image-based rendering method for synthesizing free-viewpoint images from a set of multi-view images. In LFR, no/little knowledge of geometry is required, since scene objects are assumed to be at a constant depth. This assumption causes focus-like effects on synthetic images, in which only the objects near to the assumed depth are synthesized clearly and sharply. In order to generate all-in-focus synthetic images, the authors proposed a focus measurement method which uses several kinds of reconstruction filters. Using this method, we can detect in-focus parts on multiple images that are synthesized with different assumed depths, and integrate them into one final image. Though this algorithm was shown to be effective for some real scenes, the optimal combination of reconstruction filters has not been discussed yet. In this paper, we introduce a detailed spatial domain analysis of this focus measurement method, and compare three combinations by the theoretical analysis and an experiment.