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<blockquote data-quote="WayneF" data-source="post: 384410" data-attributes="member: 12496">I just put a new Guide Number calculator on my page about Guide Number,at <a href="http://www.scantips.com/lights/flashbasics1c.html#calc" target="_blank">Understanding Guide Numbers</a>It does the math to convert one Guide number (at full power level) at some ISO,to a new guide number at another ISO and/or another power level.It assumes still the same zoom (same angular coverage).&nbsp; As an approximation, coverage diameter half of what it was should be 1.414x higher Guide Number, but sometimes reflector details are unknown and not linear.The calculator can work from any ISO baseline, it doesn't have to be ISO 100, but I suspect there is not much use for anything but ISO 100.&nbsp; <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile&nbsp; &nbsp; :)" loading="lazy" data-shortname=":)" /></blockquote>

[QUOTE="WayneF, post: 384410, member: 12496"] I just put a new Guide Number calculator on my page about Guide Number, at [URL="http://www.scantips.com/lights/flashbasics1c.html#calc"]Understanding Guide Numbers[/URL] It does the math to convert one Guide number (at full power level) at some ISO, to a new guide number at another ISO and/or another power level. It assumes still the same zoom (same angular coverage). As an approximation, coverage diameter half of what it was should be 1.414x higher Guide Number, but sometimes reflector details are unknown and not linear. The calculator can work from any ISO baseline, it doesn't have to be ISO 100, but I suspect there is not much use for anything but ISO 100. :) [/QUOTE]

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