Nathalie Morel, Preston
Our Brian answers all of your tricky technical questions and rates a reader’s photo
Brian Says… When the flash is set to Ext. A (auto) mode it gets the current aperture and ISO settings from the camera automatically via the hotshoe, or a radio transmitter on the camera.
If Ext. M (manual) mode is chosen, you must input the aperture and ISO on the flash itself. I sometimes use Ext. A mode for off-camera flashes that are lighting a background. Once set, the background brightness stays the same even if the aperture value changes
Ext. M can be used for light painting with long exposures, you set the aperture and ISO to ensure that each flash is the correct brightness.
Ext. M and Ext. A modes use a light sensor on the flash to measure the light, and the amount of light is determined by the flash, not camera
Flash set to Ext. A lights behind the model, ensuring the exposure is consistent