The Flash Photography Adviser app automatically proposes balanced settings, and subsequently supports changing these settings to achieve a new equilibrium, for:

- Flash Coverage (Zoom),

- Flash Output (Power Level),

- Flashgun-to-Subject Distance,

- Camera ISO,

- Camera Aperture,

assuming a shutter speed that is at or below the camera's maximum flash sync speed, and where the flashgun-to-subject distance is measured along the path that the light travels from flash to subject.

Each such an equilibrium represents a correct exposure in accordance with the guide number rule.

The guide number rule is a handy rule of thumb in flash photography; the rule estimates the required flash exposure value without using a light meter.

This rule evolves around three concepts:

- Incident light (as opposed to reflected light); an advantage for `difficult' subjects (for example bright or dark scenes).

- The different lighting conditions that occur when (a) zooming your flashgun, (b) changing the flash-to-subject distance, or (c) changing the flash power

- The relatively fixed exposure value for the light from the flashgun under these conditions

What the rule does NOT prescribe are the actual flashgun and related camera settings (aperture, ISO, flash power, flash zoom, flash-to-subject distance) that you can use, as long as the combination of manual flashgun and camera settings lead to an equivalent exposure value as specified by the rule. Often, there are many of such equilibria.

The Flash Adviser will assist in finding these equilibria by indicating how to achieve balance (the deviation as well as the direction), and indicating when balance is achieved. For this, the app indicates the resulting overall exposure value in stops RELATIVE to the rule for a selected lighting condition.

Also, in the balancing process, you can choose to balance to a flash exposure compensation value rather than balancing to the zero value. For instance, you can use this feature for compensating for specific light modifiers (e.g., a shoot-through umbrella, a softbox) or to achieve balance between flash light ambient light.

In this convenient app you can define and store your own flashgun(s). The app estimates the required exposure value based on the (zoom-value dependent) guide numbers of the flashgun. These guide number values can often be found in the specifications section in the