Class 1 · Exposure
24 fps → 1/48 · 30 fps → 1/60. The 180° shutter is the film look. It never moves to fix exposure.
Each step is one stop: double or half the light.
A teaching model. The scene is rendered with real distances (leaf 0.5 m, slate 1.5 m, street 12 m, trees 40 m), and the blur follows a lens focused on the slate. Real cameras have finer steps.