The Flash Power iPhone App is combination camera flash calculator and depth of field calculator.
Based on guide numbers provided by the manufacture of a flash unit, the calculator will determine either the maximum flash distance for a given aperture or the necessary aperture for a desired subject distance. The guide numbers given out by a flash vendor are normally based on a rating for the flash using an ISO of 100 and the distance in meters. The calculator will perform the conversion to use other ISO stops. The distance given will automatically be converted from meters to feet in the calculator.
Version 2.0 added an option to select the power setting on the flash calculator. The selections include Full, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 and 1/128. Using the inverse square law, the calculator will provide the flash drop off distances for 25%, 50% and 75% of power setting.
The depth of field calculator includes a large selection of camera manufacturers and models. This list is used to provide the basis of the depth of field calculation. If your camera is not listed, you will be able to add the manufacturer and model. The "Circle of Confusion" value must be provided for the depth of field to be calculated.