Rectus

Rectus was the name of a shutter found on some Japanese cameras from the 1950s. According to a post in the Classic Camera Repair Forum it was a copy of the Prontor II. According to this page at Japan Family Camera, it was made by a company called Fuji Seimitsu (富士精密), together with the Ceres shutter.

Cameras equipped with a Rectus shutter

This list is incomplete. That a particular model is listed here should not be taken to mean that all examples were fitted with a Rectus shutter.