The Super D was the successor of the Graflex Series D used by the famous Dorothea Lang during the depression era.
The Super D has a focal plane shutter as well as a front shutter just like its predecessor.
These cameras accept the slotted-type Graflex holders: there is a groove down each side of these holders, and sliding bars fasten them to the rear of the camera.
NOTE: These cameras do NOT accept modern 4x5 holders, which are slightly different in size, and lack the grooves.
It is said that the automatic diaphragm was invented and patented by a Chicago photographer Torkel Korlin (1903-1998).
The Super D sales did not came up to expectations, reason why Korling decided not to renewal the patent.
This is the basic principle of the operation of each Graflex camera model.