Flash Power+

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Apple App Store

Flash Power Calculator


The Flash Power+ iPhone App is a camera flash 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.

With version 2.0, FlashPower+ is also a depth of field calculator. Click here for instructions.


Flash Power Calculator Screen

Flash Power Calculator Screen

The calculator functions with five basic parameters: ISO, guide number from the manufacture, aperture, flash power setting, and distance.  Based on a given ISO, guide number and power setting, the app will determine the fifth when given either the aperture or the distance.  When the aperture is entered, the distance is calculated.  When given the desired distance, the aperture will be determined.

New with version 2.0, the calculator will display the distances of power drop off for 25%, 50%, and 75%.


ISO Table

ISO Table

The ISO value is selected from one of two tables.  On the primary screen, there is a toggle button under the ISO value.  The switch can be set to "in Thirds" or "in Stops".  Tapping will switch from one value to the other.

Depending on the switch setting, the app will allow you to select ISO values either in full stops or third stops.

Switching from "in Thirds" to "in Stops", the ISO value will change to the next full stop if the value is not already a full stop value. For example, if a value of 160 has been selected and the button is pressed, the value will automatically change to 200.


Aperture Table

Similar to the ISO Table, the aperture is selected using three lists.  The table is selected using the toggle button under the f/Stop value.  The switch can be set to "in Stops", "in Halves", and "in Thirds".  

Depending on the setting, the aperture value can be set to the respective f/stop values.

Switching the table will cause the value to round to the next value if necessary for that table.  For example, going from thirds or halves to full stops will cause the value to go up to the next value.  Also switching from thirds to halves or visa versa will also cause rounding "up".  For example, if "f/4.5" has been selected and the button is pressed to change to full stops, the aperture value will be changed to "f/4.0".


Guide Number

When entering the guide number, the input field is tapped and a custom keyboard is displayed to allow input using only numeric values. The keyboard is dismissed by pressing the enter key or by tapping anywhere off the keyboard.

The guide number can be entered based on feet or meters.  Most manufactures' values provided are in meters, so this functionality may never be used.  Actually doing guide number calculations is beyond the functionality of this app.



When entering the distance to calculate the aperture, the input field is tapped and a custom keyboard is displayed to allow the input of the distance using only numeric values with a decimal point.

The distance can be entered either in feet or in meters.  The button under the input field will toggle between "in Feet" and "in Meters".  If there is already a value in the field the calculator will automatically switch between the two units.


Other Stuff

The calculator remembers the selections that you have made from one use to another. Once the guide number is entered, the value is kept until you change the value. All of the toggle buttons remain as the last value that you selected.

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