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Sigma EF530 Guide Number

mcgovernjon 11 138 United Kingdom
12 May 2009 1:03PM
The Sigma EF530 flashgun apparently has a guide number of 53, though there is a footnote saying "at 105mm". Does this make the guide number different to the way it is measured on other flashguns?

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strawman 16 22.1k 16 United Kingdom
12 May 2009 1:12PM
If the flash gun has a zoom head, then the guide number will vary with the zoom head. Think of the gun having a maximum light level. At its wide angle end it has to cover a much larger space, so the distance falls. Zoom the head to longer lens setting and it can illuminate objects further away.
mcgovernjon 11 138 United Kingdom
12 May 2009 1:44PM
OK, thanks... so are all guide numbers measured at 105mm?

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