Thanks,it makes sense
One more question. At the "Auto Flash + Exp. Comp." option, to get auto flash exposure should I let the first parameter unchecked,or should I check it and set the second parameter to 0 ?
The default on Canon cameras is to use ETTL metering for the flash.
The camera measures the amount of light from the flash and turns off the flash when it thinks the exposure is correct.
Some cameras allow you to set the flash to Auto (ETTL) or Manual, and in Auto mode to set the flash exposure compensation (which affects how the flash exposure is calculated). In manual flash mode you can set one of three power levels (min, med, max).
Other cameras give you no control over the flash, other than to turn it on or off.
Finally on cameras that have a manual (M) shooting mode, Canon forces the flash to manual mode and only allows you to set one of three power levels.
The CHDK flash overrides give you the same controls as the above Canon functions, auto with flash exposure compensation, or manual with three power levels.
You can use the CHDK 'Auto Flash + Exp Comp' override in the following cases:
- your camera does not have built in settings for flash exposure compensation and you want to adjust the flash power; but still use ETTL metering overall
- you want to enable ETTL flash in M mode
Unless you are shooting in M mode, then enabling 'Auto Flash + Exp Comp' with 0 compensation is equivalent to the default Canon flash settings - the two options you presented should produce equivalent results.
Phil.
