Guide Number

Matt

Matt

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matt
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when a flash spec says Guide Number: 14m/46ft, what does it mean?
 
With the flash head in the "normal" operating position (i.e. straight on) and the camera set to 100ISO, you'll get a correct exposure at a range of GN/ƒ-stop.

Tweak ISO and ƒ-stop accordingly and guesstimate the losses from bouncing. The flash's manual should detail the effect on GN of the zoomhead.
 
matty said:
when a flash spec says Guide Number: 14m/46ft, what does it mean?
Click to expand...

At ISO 100 you can illuminate a subject 7m away at f/2.0

Basically distance= GN/f-stop

Higher the GN, greater the power.

If you were shooting @ f8, a low-powered flash like a GN14m would only illuminate up to 1.5ish metres, but obvious you could stretch this by pushing up the ISO.

HTH

Phil
 
hello

Yeah, got it thanks. So GN14 on a ring flash is ok for macro and at a push some portraits (push the ISO up a bit..)
 
matty said:
hello

Yeah, got it thanks. So GN14 on a ring flash is ok for macro and at a push some portraits (push the ISO up a bit..)
Click to expand...


Definitely - also fine for daylight fill-in, but you need the 430 / 580 / third party equiv for serious room-filling bounce flash stuff.

Phil
 
ive got a sigma flash, but looking at the ring flash Ive got in mind im not sure if i can fire it remotely (7d and sigma 500dg super, looking at marumi macro ring flash)
 
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