FEC and the 580EX

I have noticed that several different interpretations have been described on this forum pertaining to the way in which FEC logic is implemented on the 580EX. This led me to perform my own evaluation yesterday using the 580EX on my XTi. Results may be different for other Canon DSLR models, but I suspect not.

UPDATE: I have discovered that my description is not quite correct after repeating the test. The only times that the FEC will revert back to the camera's settings is one of the two following situations:

1. The FEC on the flash is set to zero.
   
2. The mode dial on the camera is switched to a basic mode (ie, the green box) and then back to one of the creative modes. Switching to a basic mode essentially resets the flash FEC to zero.

When the flash FEC is set to a non-zero value, then that value will be used instead of the camera's FEC value (this is true except for the caveat noted above). And, when the flash FEC is set to zero, the FEC value of the camera will be used (this stattement is always true).

Since this and several other interpretations seemed to be at odds, I conducted my own evaluation and the following is a summary of what I learned:

What I found is that after initial “power-up”, the camera's FEC will be used unless the FEC is changed on the 580EX after a particular mode is selected, such as Program AE, etc. That change will remain in effect until you do one of the following -- change to one of the other shooting modes, change the camera’s FEC, or turn the camera off (this whole statement should be revised to say that the FEC of the flash will remain in effect unless the shooting mode is switched to a basic mode such as full auto and then back to one of the creative modes. Doing so will reset the flash to zero FEC which means that the camera FEC will then be used).

A simpler way of phrasing this to make it easier to remember would be, "the camera's FEC applies, but can be temporarily overridden by the flash's FEC, where the term temporarily means, "until any camera setting is changed." (Disregard this and see the two cases mentioned at the beginning of this post).

LEGAL NOTICE: I believe the above results to be well intentioned, but possibly misguided. Your actual mileage may vary and is void in states where prohibited. This information is not warranted to be fit for any particular purpose and is provided “as is.”

I might also add that in the Basic modes, you are at the mercy of whatever the camera wants to do. There is no way of changing the FEC in the camera or the flash.

Can you explain what you mean by 'after initial “power-up”, the camera's FEC will be used'? If I have FEC set on the flash, it doesn't matter what my camera FEC is set to, and whether I've just turned on the camera or not, the FEC used is always the FEC set on the flash. The only way I can ever use the FEC set on the camera is to set the FEC on the flash to 0.

So I'm really curious to know how you managed to use the FEC on the camera when you have FEC set on the flash. Please elaborate further.

What I meant by "initial power-up" is simply "turn the camera and flash on". Maybe your camera is different than the XTi or maybe I was in the Twilight Zone. I will repeat what I did to see if I was hallucinating. I did my tests using the ETTL-II mode of the 580EX and I was looking at the "Creative" shooting modes on the camera (Program AE, Tv, and Av). I did not check how Manual operated. I apoligize if I gave bad information, but I believe that I saw what I reported here and will quickly correct things if I made an error. the last thing that I want is to spread bad information.

OK, I need a good recipe for crow! I think that maybe my head is unstuck now.

My earlier description needs some major caveats. In my previous test, I would switch the camera to the green box and then back to one of the creative modes. I learned something new tonight -- if I change to one of the basic modes like full auto, whatever FEC is in the flash gets reset to zero and when I switch back to a creative mode such as P, the FEC will default to whatever is in the camera.

Also you are not quite correct in your statement that "the FEC used is always the FEC set on the flash". That is not true if the FEC on the flash is zero. In that case, it is the FEC of the camera. Of course, you probably figured that any fool should know that part anyway.

I realize that since most of you pro and serious amateur guys never bother with the basic modes, I will have to shamefully admit that I do still use the basic modes a bit and so this little interesting quirk might only be relevant to know-nothing peons like me.

I will modify the original post to correct my error and then retreat to the corner with my dunce cap on and enjoy my crow dinner.

bill boehme wrote in post #2841063
OK, I need a good recipe for crow! I think that maybe my head is unstuck now.

My earlier description needs some major caveats. In my previous test, I would switch the camera to the green box and then back to one of the creative modes. I learned something new tonight -- if I change to one of the basic modes like full auto, whatever FEC is in the flash gets reset to zero and when I switch back to a creative mode such as P, the FEC will default to whatever is in the camera.

Also you are not quite correct in your statement that "the FEC used is always the FEC set on the flash". That is not true if the FEC on the flash is zero. In that case, it is the FEC of the camera. Of course, you probably figured that any fool should know that part anyway.

I realize that since most of you pro and serious amateur guys never bother with the basic modes, I will have to shamefully admit that I do still use the basic modes a bit and so this little interesting quirk might only be relevant to know-nothing peons like me.

I will modify the original post to correct my error and then retreat to the corner with my dunce cap on and enjoy my crow dinner.

It really helps to read the complete paragraph. Note the last sentence in the paragraphy.

I could have left it out and still been correct since, theoretically, having the FEC at 0 means that FEC has NOT been set. But, I knew someone would argue this case, just like you did, so I purposely put that last sentence in so that there would be no argument about what I said (or so I thought ).

But that is an interesting obvervation you made about the flash FEC resetting to 0 when you switch the camera to one of the Basic mode settings. Interestingly, when using the internal flash, the camera does not reset the FEC to 0 when switched to Basic mode.

Having said that, though, what has been said about the flash FEC overriding the camera FEC, unless the flash FEC is set to 0, still holds true, doesn't it? Even when the camera was switched from AUTO or one of the other Basic modes to P, Av or one of the other Creative modes.

PacAce wrote in post #2842487
It really helps to read the complete paragraph. Note the last sentence in the paragraphy.

Sorry about not reading carefully enough.

PacAce wrote in post #2842487
Having said that, though, what has been said about the flash FEC overriding the camera FEC, unless the flash FEC is set to 0, still holds true, doesn't it? Even when the camera was switched from AUTO or one of the other Basic modes to P, Av or one of the other Creative modes.

I ws OK with this until the second sentence and now I am a bit confused about what you are saying unless you mean when you turn the camera and flash on while it is set to a basic mode and there is a non-zero value set in the flash FEC. Afterwards, however, if you switch to a basic mode and then back to a creative mode, the flash FEC gets reset to zero and defaults to the camera FEC.

Anyway, I think that I understand how it works even if I can't seem to explain it very well. Actually, crow tastes pretty good when properly prepared.