Flash

Flash is a short burst of artificial light used to brighten a subject when natural or room light is too dim. It can come from a built-in unit, an external speedlight, or a studio strobe. The burst lasts a tiny fraction of a second, which freezes motion and adds enough illumination for a readable exposure in dark environments.

Built-in flash is part of the camera body and sits close to the lens. It is convenient but limited in power and direction. External flash mounts on the hot shoe or fires wirelessly, offers more power, can tilt and bounce, and accepts modifiers. External units give more control over light quality and reduce problems like red eye.

Shutter speed mainly controls how much ambient light records, not how bright the flash-lit subject appears. At or below the camera's flash sync speed, the shutter is fully open during the burst. Faster shutter speeds darken the background while flash exposure stays similar. Slower speeds pull more room light or sky color into the frame behind a flash-frozen subject.

Aperture controls how much of the flash burst reaches the sensor. A wider aperture lets in more flash light, brightening the subject. A smaller aperture reduces flash brightness. Shutter speed and ISO still shape ambient exposure, so photographers often set aperture to match desired flash power and depth of field, then adjust shutter speed for the background.

TTL flash metering measures light through the lens during the exposure and adjusts flash power automatically. The camera fires a pre-flash or reads reflected light to decide how strong the main burst should be. TTL helps in changing conditions, such as events where subjects move and distance shifts, though manual flash power gives more predictable results in controlled studio setups.

A typical method sets ambient exposure for the background using shutter speed, aperture, and ISO, then adds flash to light the subject. Raising ISO or slowing the shutter speed brightens the ambient scene. Increasing flash power or opening the aperture strengthens the subject without changing background brightness as much. The mix keeps rooms and skies visible while faces stay well lit.

Bounce flash points the speedlight at a ceiling or wall instead of directly at the subject. The light reflects and spreads over a larger area, producing softer shadows and more flattering portraits than straight-on flash. White or neutral surfaces work best. Colored walls can cast unwanted color onto skin, so bounce direction and surface choice matter.

Red eye happens when flash light enters the eye, reflects off the blood-rich retina, and returns to the camera lens. It is common with on-camera flash because the light source sits near the lens axis. In low light, dilated pupils let more light in, making the effect stronger. Bouncing flash, moving the light off-axis, or using red-eye reduction pre-flashes can reduce it.

Flash sync speed is the fastest shutter speed at which the camera can fully expose the sensor while the flash fires. Above that limit, the shutter uses a moving slit that can clip part of the burst, leaving dark bands in the image. Sync speed varies by camera; many bodies sync around 1/200 s or 1/250 s unless high-speed sync is enabled on compatible flashes.

Flash fills shadows on faces in bright sun, balances backlight when a subject stands against a bright sky, and adds catchlights to eyes in shade. A low-power burst can lift dark areas without overpowering the scene. Fill flash is common in outdoor portraits and wedding work where harsh midday light or strong backlight would otherwise leave subjects underexposed.