Make sure the subject is within the flash range. (To obtain well-exposed images, the subject must be within the flash range.
Please refer to the instruction manual before using the flash.
Flash coverage changes according to the camera sensitivity. (However the noise in image may become noticeable by increasing the camera sensitivity.)
It can be checked on the LCD monitor if the flash reached or not after flash burst.
If the subject is not within the flash range, use of program flash is recommended.