YN-460II Speedlight with GN53 for Canon Nikon Pentax Olympus Sony DSLR cameras

It is the best recommandation as a slave flash for photography.
It has Optical Slave and Fully Manual function, and most important, the GN number is increased to 53.
 

Technical parameters:
* Guide number:
* 38 (at 35mm focal length, ISO 100 in meters)
* 53 (at 35mm focal length, ISO 200 in meters)
* Flash mode: M, S1, S2
* Flash power control : Level 46 light quantity output control with 1/7-stop increment
* Circuit design: Insulated Gate Bipolar Transistor (IGBT)
* Vertical rotation angle : -7~90 degrees
* Horizontal rotation angle : 0~270 degrees
* Power: 4 x AAsize batteries (Alkaline or Ni-MH are usable)
* Lighting times: 100 to 1500 times (AA alkaline cell used)
* Recycle time: approx 4s (AA alkaline cell used)
* Color temperature : 5600k
* Flash time :1/800s~1/20000s
* Dimensions: 72 x 135 x 85mm
* Net weight: 250g
* Accessories: Flash light (1), Protecting bag (1), Mini stand(1) User manual (1)