Because the metering systems of this camera, both ADI and P-TTL use the reflection of pre-flash to adjust flash output, the previous type external flash units that do not support pre-flash function cannot be used. Such external flash units will fire with full output when attached to DiMAGE 7, which requires the manual calculation of exposure from the aperture setting and the subject distance. General formula to calculate an optimum exposure is as below: Guide Number / f-Number  = Subject Distance (at ISO 100) If the Automatic setting of  camera sensitivity is selected, turn the control-dial for two clicks to select a larger aperture opening by one-stop, e.g. f/5.6 to f/4, f4 to f/2.8