In certain exposure modes on your Nikon D3400 camera, flash is set by default to fire automatically if the camera thinks that the ambient light is insufficient; in other modes, you have to manually enable the flash. Here's the breakdown:
- Auto mode; all Scene and Effects modes that permit flash: Flash is set to Auto by default. After you press the shutter button, the camera assesses the available light and automatically pops up the built-in flash if it finds that light lacking. If you don't want to use flash in these exposure modes, you may be able to disable it via the Flash mode setting, however.
- P, S, A, and M modes: There's no such thing as automatic flash in these modes. Instead, if you want to use the built-in flash, press the Flash button on the side of the camera. Don't want flash? Just press down gently on the top of the flash to close the unit.
The camera does give you a little flash input, though: You see a blinking question mark or a flash symbol, or both, in the displays if the camera thinks you need flash. Press the Zoom Out button (the one with the question mark above it), and a message appears, recommending that you use flash.
