BlattWorld, Item Details: Nikon SB-21A Macro Speedlight

TTL Macro Speedlight SB-21 A For Brilliant Close-Up Detail
SB-21A for F3-series cameras.
Designed specifically for close-up photography
Dual, rotatable flash tubes allow you to select flat front lighting or selected relief lighting
Advanced electronics assure consistent exposure control with variable output
Built-in focus illuminator aids manual focusing
Further lighting enhancement is possible using secondary lighting or reflector systems (because exposure control can be completely automatic, no special calculations are required when using these systems)
Ideally suited for use with all Micro-Nikkor lenses.
Guide number (ISO 100 in feet) 43 with internal batteries (49 with external power source)