When flashes first started to use Guide Numbers, they were a fairly reliable judgement of how one flashes power stacks up against another. But as flash technology has evolved, the humble Guide Number is often exploited as a marketing gimmick to make flashes sound a lot more powerful than they actually are.
In this video, Gerald Undone breaks down the maths behind the Guide Number. He explains exactly how it’s calculated, why it isn’t always an accurate measurement of power, and how you can make sense of it all.
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