Online Tutorials: Flash Photography

The important factor in flash photography is to artificially provide enough light for the film to sufficiently react to the image exposed to it. To remain successful, the amount of light and exposure must be controlled.


Exposure control

With a manual flashgun you will need to calculate the aperture from the guide number.

Automatic flashguns have a sensor on the flash which measures how much light is reflected from the subject and tells the flash when to cut off.
Dedicated flashes use through the lens (TTL) flash metering in which the flash sensor is inside the camera and the camera controls the flash duration directly.


Guide number:

The guide number (GN) of a flashgun is a measure of its power and is based around a standard of ISO100. For a manual flashgun, the aperture required for a subject distance 'd' is calculated by:

aperture = guide number/d

For example, for a flashgun with a guide number of 32m and a subject 2m away, the aperture is f16 (i.e. 32/2). With automatic and dedicated flashguns, this is automatically calculated and the power is adjusted, although there is still a maximum limit to its useful operation.

Flashguns / speedlights were covered in some detail in the accessories section and here is a reminder of the types that are commonly used by most people.


Built in flash

built in flash

Simple to use and convenient but has little range or power.

Hotshoe mounted flash

hotshoe flash

Versatile - can bounce and change the angle the light falls at, but needs its own power supply and can be bulky.

Off camera flash

off camera flash

Works exactly like a hotshoe mounted flash, but with more opportunities to move the light course around the subject. Useful for backlit photography. This method also includes wireless triggers.



A ringflash is a very soft and direct flash for portrait and flower photography. It produces pleasing results as it spreads light evenly around the subject.


Strobe Light

strobe flash

These are particularly useful when in a studio situation and act effectively as larger speedlights.

They are often triggered in the same way as an off camera flash, i.e. via cable or remote trigger. Easy to attach a reflector / umbrella to the main body of the unit.