NEed some Help in Flash knowledges!


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nebula

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Mar 7, 2004
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#1
Hi all,

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.. :dunno:

hope some one can elighten me.. THAnKS
 

clive

Senior Member
Oct 9, 2002
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#2
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
 

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