Lens imaging is a classic topic in physics education. To guide students from their holistic
viewpoint to the scientists’ analytic viewpoint, an image-based approach to lens imaging has
recently been proposed. To study the effect of the image-based approach on undergraduate students’
ideas, teaching experiments are performed and evaluated using qualitative content analysis. Some of
the students’ ideas have not been reported before, namely those related to blurry lens images, and
those developed by the proposed teaching approach. To describe learning pathways systematically, a
conception-versus-time coordinate system is introduced, specifying how teaching actions help
students advance toward a scientific understanding.