Flash

With the advent of E-TTL measurement, and the ability to get correct flash exposures without thinking too much, it may seem that the ability to adjust the flash power manually is a turning back. However, while E-TTL works most of the time, there are still those who prefer to have full control over the flash in certain situations.

This calculator allows you to determine the maximum illumination distance of your flash depending on your aperture or focusing distance.

For those of you who are not fully aware of guide numbers - the guide number (GN) is a measure of the power of a flash. The higher the GN, the stronger the flash.

Use

The tool allows you to either determine:

• the subject max. distance according to the chosen aperture (mode 1)
• the smallest aperture to use according to the subject's distance (mode 2)

Mode 1

1. Unlock the aperture by clicking on the ?

2. Set the desired focal length as well as the ISO, flash output and guide number of your flash by turning the wheel or by clicking to enter the value

In the bottom area

3. You get:

• The distance max. on the subject (11.79 ft)
• The amount of flash light illuminating the subject

Mode 2

1. Unlock the focus distance by clicking on the ?

2. Set the ISO, flash output and guide number of your flash by turning the wheel or by clicking to enter the value

3. Set the unit of focus distance

4. Set the focus distance

In the bottom area

5. You get:

• The smallest aperture to use (3.30 mm)
• The amount of flash light illuminating the subject