Reply to thread

Message

<blockquote data-quote="WayneF" data-source="post: 383967" data-attributes="member: 12496">GN is about what the light meter might measure.&nbsp; GN is a simple calculation that simplifies the inverse square law falloff.GN / distance = fstop.GN 60 means 1 meter at f/60, or 6 meters at f/10, or 10 meters at f/6, etc (and any other combination)..But what the light meter reads depends on both the power level, and also the reflector coverage.&nbsp; A wide reflector might illuminate the entire wall (distributing the power), where a narrow reflector concentrates the power into just a bright spot on the wall.&nbsp; &nbsp; The same flash unit will have very different GN in these cases (what the light meter will read is very different).&nbsp; We can only compare GN at the same coverage angle.&nbsp; It takes much power to illuminate the whole wide wall, much less power to light a small spot on the wall.&nbsp; If comparing same known coverage, the GN can compare power levels, but unknown coverage tells absolutely nothing.&nbsp; GN is as much about the reflector as it is about the power.For the GN 60 to have meaning, it has to specify how it is measured (what reflector coverage, etc).&nbsp; It probably means the provided bare reflector, which would let us use GN (with that bare reflector), but to compare it, we have to know what coverage that is.&nbsp; We can only compare GN at like coverages.&nbsp;Speedlights zoom the reflector, and of course they have many GN, for each zoom coverage (see the GN chart in the manual).Use an umbrella or a softbox or a grid, and it will change the GN.&nbsp; The light meter will be vastly more useful for studio lights.Speedlights can use GN for direct bare flash, but it is unknown for bounce, or for umbrellas, etc.</blockquote>

[QUOTE="WayneF, post: 383967, member: 12496"] GN is about what the light meter might measure. GN is a simple calculation that simplifies the inverse square law falloff. GN / distance = fstop. GN 60 means 1 meter at f/60, or 6 meters at f/10, or 10 meters at f/6, etc (and any other combination).. But what the light meter reads depends on both the power level, and also the reflector coverage. A wide reflector might illuminate the entire wall (distributing the power), where a narrow reflector concentrates the power into just a bright spot on the wall. The same flash unit will have very different GN in these cases (what the light meter will read is very different). We can only compare GN at the same coverage angle. It takes much power to illuminate the whole wide wall, much less power to light a small spot on the wall. If comparing same known coverage, the GN can compare power levels, but unknown coverage tells absolutely nothing. GN is as much about the reflector as it is about the power. For the GN 60 to have meaning, it has to specify how it is measured (what reflector coverage, etc). It probably means the provided bare reflector, which would let us use GN (with that bare reflector), but to compare it, we have to know what coverage that is. We can only compare GN at like coverages. Speedlights zoom the reflector, and of course they have many GN, for each zoom coverage (see the GN chart in the manual). Use an umbrella or a softbox or a grid, and it will change the GN. The light meter will be vastly more useful for studio lights. Speedlights can use GN for direct bare flash, but it is unknown for bounce, or for umbrellas, etc. [/QUOTE]

Verification