What is a non-dedicated (manual) flash?
The basic flash unit is a manual flash. It consists of a light source with no specific interface to the camera other than a trigger signal. The user must set such things as flash output (a percentage of the full output), any zooming to cover the angle of view, and so forth. Typically, manual flash units are much more powerful (ie, have higher GNs) than dedicated flash units, because more space can be devoted to flash electronics instead of camera interface electronics. With a manual flash, the operator must be very aware of the GN, the aperture, and the flash to subject distance to correctly compute the exposure settings.