The Nikon Speedlight SB-18 is a compact, direct-mounting electronic
flash unit which provides automatic through-the-lens (TTL) control of the flash exposure when used with the Nikon FG, FE2, or
FA, or the Nikonos-V via the V-Type Sync Cord. Because light is measured through the actual picture-taking lens, you are assured of just the right exposure with a variety of lenses and accessory attachments at any aperture from f/2 to f/16.
Through the use of a silicon-controlled rectifier and series circuitry, the S8·18 is able to conserve energy when shooting subjects at close range; thus recycling times are shorter and the number of flashes per battery set is greater.
The S8-18 is also compatible with most Nikon cameras for manual operation. In addition, the SB-18 couples with the flash ready-light inside the viewfinders of current Nikon
cameras. As soon as the flash is ready to fire, the LED comes on.
In my opinion it is a practical flash unit to old Nikon SLR cameras.
I do not know if it can be used with the new digital cameras.