Specification:                   
Flash index: GN20m (ISO100, DIN21)            
Color  temperature: 5600K            
Illuminating  angle: Horizontal 60°, Vertical 40°            
Recovering time (sec.): 7            
Flash duration (sec.): 1/1000            
Triggering method: low voltage trigger            
Power source:  2xAA batteries (NiDd and NIMH chargeable batteries can be used)            
Dimension (mm): 65x60x98                              

Compatible with      
All ordinary digital camera and  traditional cameras. Except Minolta and Sony anti-intercalation Shoe. Even if  there is no hot shoe, through the primer flash can also be used successfully.   

How to use:         
Index (GN)=aperture (F) x distance (L) For example: If the photo nasty is  ISO100/DIN21, the distance between the camera and the main feature is 5m, then  the aperture is approximately F/4.       
Fix the distance between camera and the object by your eye, and then find the parameter  on the exposure meter.            
Find the photo nasty of your camera from the first vertical line of the left exposure  meter. The joint of this two lines is approximately the aperture number.            
You can also get your aperture number from the following formula