In Program mode, TTL always selects an aperture value based on the level of available light. With FE Lock, the Speedlite 380EX or 220EX preflash fires when the camera's AE lock button is depressed, storing AF and metering data for up to 16 seconds. FE lock is extremely useful when you wish to place the main subject in a part of the picture area that is not covered by one of the three focusing points. It can also eliminate potential exposure errors caused by unwanted reflections from highly reflective surfaces like windows or mirrors. Therefore, even in bright daylight conditions, a fast lens can be used at a wide aperture to blur the background and emphasize the subject in portraiture, for example.
FP flash is automatic and simple to use.
Flash Exposure Compensation Flash exposure compensation adjusts the level of illumination provided by the flash, and is therefore an important method of creative control for all kinds of flash photography. Instead of firing the instant the shutter opens, Second-curtain Sync fires the flash at the end of the exposure, allowing streaks of light to flow naturally behind the movement of the subject.