Notes on Using On-Camera Flash
Guide Number - Refers to the strength of the flash (brightness) -usually at ISO 100
GN = f.stop x distance
GN100 f.2@50feet
GN100 f.4@25feet
Flash Exposure done by modifying the aperture only. The shutter speed does not determine the exposure of the flash lighting.
Flash Sync Speed - varies from camera to camera, usually 1/30 to 1/200s
High Speed Sync - up to 1/8000 useful for large aperture on sunny day
Dragging the Shutter - using both ambient and flash light, set the shutter for the correct ambient light exposure.
-the flash exposes the foreground, and the ambient exposure exposes the background.
-Moving objects are frozen by the flash exposure, and may blur with long ambient exposures.
-typically the best results occur when the ambient exposure is 1-2 stops down from the correct exposure.
2nd (rear) curtain sync - flash fires at the end of the exposure
Fill Flash
-used to fill in the shadows for more even lighting - set to minus 2 or minus 3 stops
-used to illuminate the subject against a bright background-silhouette -underexpose the background and correctly expose the subject with flash
TTL Through the Lens Metering
the flash and camera sends out a pre-flash and the exposure set using a sensor in the lens. May be coupled to the focus distance
Flash Exposure Compensation
works just like camera exposure compensation and allows you to vary the amount of flash exposure.
Bounce Flash
aiming your flash at a ceiling or wall converts into a larger light source which is a softer light source. Straight flash is quite harsh lighting. -Wall color
Off Camera Flash
wired - 6” to 33’, straight or coiled, usually proprietary
wireless - infrared, radio and optical
-optical - slave -not TTL
-radio full TTL, no direct line of sight needed, different channels
-optical TTL, direct line of sight needed
little faster than radio
Modifiers and Gels
-modifiers to control light direction or to soften
-Gels are used to modify light color
-Wide Angle diffuser built into the flash - to 17mm
Tips
-flash should usually be used to complement the ambient light, not to overpower it
-direct flash and high shutter speed is almost always a no-no.
-Bounce the flash for better directional lighting and softer light
-Drag the shutter - balance the ambient with the flash exposure
Problems
- Uneven lighting - subjects should be the same distance from the flash - inverse square law
- Shadow on the Wall
- Unwanted Reflections - in glass or eyeglasses
- Uneven Coverage