30th May 2004, 11:28 PM
NEed some Help in Flash knowledges!
Hope that anyone out there would be kind enough to help me solve some doubts about flash
wat's does it mean by saying :
GUIDE NUMBER (ISO 100, M/FT.)
38 / 125 (at 35mm) to 56 / 184 (at 105mm)
Guide number (ISO 100, m):
36(with Zoom head set at 35mm)
I understand is mentioning something about guide no.. but.. can't understand..
hope some one can elighten me.. THAnKS
31st May 2004, 02:11 AM
guide number (GN) is a value representing the "power" pf the flash
its unit is in "metre" or "feet"
in the olden days, people use this equation: GN = A x D
A: aperture (numerically, no units)
D: distance from camera to subject (numerically, unit is either "metre" or "feet")
so if ur flash has GN = 40m, u prepare to shoot @ f4, then if u position your model at 10m away from the camera, the flash at 100% output will then supposedly give u a "nice" flash exposure. (18% reflectivity) because u follow the equation. (40=4x10)
for your flash, the GN is variable and it increases as u zoom the zoom head on the flash.
so at 35mm, your flash GN is 38m which is 125 feet. (one feet = roughly 0.333m)
likewise at 105mm, your flash GN is 56m which is 184 feet
it says the GN is 36 when zoom head is set at 35mm...this is a bit redundant which is ok, since GN=36m is practically the same as GN=38m both @ 35mm