By setting the flash on manual, you disengage the sensor. The exposure should be correct as long as you remain within the recommended range for the mode you're using. When you take a flash picture against a dark background, the flash sensor may put out too much light for the subject, thereby overexposing it. Photo Contest Exposure with a Built in Flash Many compact and some advanced SLR cameras have small electronic flash units built into them. You can use them as a main flash indoors or as a fill light outdoors.
Some cameras automatically turn on the flash in dim light.
Other cameras flash an indicator or beep to tell you to switch on the flash. Typically, the flash begins charging as soon as its activated, and on most models, an indicator light in or near the viewfinder will tell you when the flash is fully charged. One way to keep some pop-up flash units from firing is to hold your finger on top of it to prevent it from popping up. Read your manual first to make sure that this won't damage your camera. Cameras with built-in flash are particularly suited to outdoor fill flash work, and many are programmed to create an accurate exposure balance between flash and ambient light automatically.