Re: Understanding Exposure
Kelly,
What you have posted is a chart of guide numbers for manual settings for an unidentified flash attachment. Across the top is the focal length of the lens in use (and, presumably, the focal length you have set on the flash). The left hand column is, obviously, the flash output (strength) you have set on the flash; from full power (1/1) thru 1/128 of full power. The body of the chart gives the guide numbers (meters/feet). These guide numbers are used to determine the appropriate aperture: divide the guide number by the distance from your subject = f stop.
E.G. With the flash adjusted for a 70mm lens and set at 1/4 power: If you were 5 meters from the subject, the aperture should be set at f:5.0 (25/5).
Note that the chart assumes an ISO sensitivity of 100. For lower or higher iso you make the appropriate adjustment.
Hope this helps.
Cheers/Mike
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