Tutorial GN, Ratios, Power and all that

[mike weeks]

mike weeks submitted a new resource:

GN, Ratios, Power and all that - Lighting by Numbers

Guide Numbers (GN)

In the days before many had meters they needed a simple way to work out what the exposure from a flashgun was. Most flashguns had something akin to a small slide rule fitted that you could move to calculate the exposure.

The output of a Flashgun is given as a guide number normally in metres but in the past it was in feet and this is usually at ISO 100.

So typically you would see something like, Guide Number = 56 (metres)

If we know the distance then we can...

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[Leroy4bz]

Thanks for posting, very interesting resource for a newbe like me.

 

[mike weeks]

Thanks for posting, very interesting resource for a newbe like me.

Remember that the science will get you so far but photography is an art so use these as a starting point.

Mike