Ability to adequately analyze educational situations is essential not only for (pre-service) teachers' occupational decisions, but also for their own professional development. This study represents an evaluation of the observation practice aimed at pre-service chemistry teachers' (N = 12) professional vision development. They attended chemistry classes in schools, discussed them in a group and independently wrote their reflections. The effect on the professional vision was evaluated using a self-efficacy questionnaire, lesson reflections analyses and semi-structured interviews. The results showed that preservice teachers significantly overestimated their ability to reflect on lessons, struggled with lesson analyses, failed to describe and analyze chemistry-specific content in contrast with their significant improvement in describing student-teacher interaction and teacher's activity -- all with medium to large effect. Although observation practice deepened their ability to notice, pre-service teachers did not change attention to individual lesson's aspects. Lesson observation therefore seems to be a suitable means of professional vision development from the richness of observed phenomena's point of view, as well as students' self-efficacy improvement, however more research in several aspects is needed to further inform (pre-service) teacher training practice.