Now a question about built in flash.

I am still confused about my flash situation. I think i am right when saying that in P mode, if you open the flash, the camera will use the flash as fill light automatically, but can someone tell me how it does this, if the meter is already at center?

Also, what does the camera do in manual mode when you open the flash? if I were in manual mod, and set the exposure a stop low, then open the flash (or any ettl flash unit), would the camera then control the power of the flash to add the extra stop and get the exposure correct? Does it do this in P mode? If so, how, cause if I metered and it set the exposure up properly before i open the flash, then what does it do if I then open the flash, it always fires, but why if I opened it when the camera already had the correct exposure settings before it was open?

It seems the manual doesn't go in to real detailed info on just what the built in flash actually does in certain situations. Would really love to know what it does in P mode and how that differs from what it does in manual mode.

Thanks

guitarjeff wrote in post #14466577
I am still confused about my flash situation. I think i am right when saying that in P mode, if you open the flash, the camera will use the flash as fill light automatically, but can someone tell me how it does this, if the meter is already at center?

Also, what does the camera do in manual mode when you open the flash? if I were in manual mod, and set the exposure a stop low, then open the flash (or any ettl flash unit), would the camera then control the power of the flash to add the extra stop and get the exposure correct? Does it do this in P mode? If so, how, cause if I metered and it set the exposure up properly before i open the flash, then what does it do if I then open the flash, it always fires, but why if I opened it when the camera already had the correct exposure settings before it was open?

It seems the manual doesn't go in to real detailed info on just what the built in flash actually does in certain situations. Would really love to know what it does in P mode and how that differs from what it does in manual mode.

Thanks

flash works different in P mode and manual mode, here's some explanation
http://photonotes.org/​articles/eos-flash/

First, P mode doesn't always attempt to meter for ambient light (that's what you meant by saying it uses the flash for fill). In bright light, it does. In low light, P mode will abandon the attempt to reach a correct exposure via ambient and will instead allow the ambient to fall to underexposure and then use the flash for main light. I don't like camera automation that isn't completely predictable, so I avoid P mode.

The reason fill light works is because the effect of the flash on bright parts of a scene will be negligible at a power level that merely brightens the shadows. So the firing of a flash tends to drop the contrast of a scene while not increasing the exposure of the highlights very much. The flash meter can see this effect and deliver the correct amount. If you pushed the whole exposure pretty much to the right side of the histogram, the selected flash power will be so low as to have almost no effect.

I am not sure if shooting with flash in P-mode or getting properly exposed shots using fill flash is more important to you, I suspect the later. Here is an article from Canon that describes how E~TTL fill flash works: http://learn.usa.canon​.com …ash_use_EOS_art​icle.shtml