Re: Flash Unit > Ok. Give me some time to get it written out. two words - guide number (!) once you learn how the guide number of the flash or flash& diffusor works, the rest falls into place pretty quickly. say you have a GN of 60 (metric) for 100 ISO (which is the same as GN 45 for 50 ISO, 90 for ISO 200, 120 for 400, etc <think stops>) divide the GN by the distance to obtain the correct aperture f stop number or divide the GN by the aperture to get the right distance to set your subject :) 60 / 6m .. aperture = f11 60/ 2m .. aperture = f32 60 at half power (GN is now 30) 30 / 6m = aperture = 4.5 or 5.6 30 / 2m aperture = f16 (note you'd be best advised to TEST 1/2 and 1/4 settings to find the actual GN rather than the stated one then write it on the flash head for later reference. k
