SIGMA LENS EF 500 DG ST Electronic Flash for Canon Mount Light Projection Angle is automatically set to match the lens between 28mm and 105mm Also covers 17mm wide angle when the built-in diffuser is deployed Red LED AF Auxiliary lamp Guide Number - 165 in feet / 50 in meters 105mm (ISO 100) Charge Time - Approx. 6 seconds w/alkaline batteries; Approx. 4 seconds w/NiMH batteries