I need a quick and dirty explanation, please...

I dont need anything totally indepth, but i could not find the simple answer to this Q anywhere.

maybe someone has a sticky for me...

What does the FEC do, and in what situations would i most likely find myself using it?

I think i know basically, but i fear i might have it backwards.

any help?

TY in advance!

Basically, Flash Exposure Compensation is used similarly to Exposure Compensation, but it adjusts the flash output rather than adjusting the camera settings that affect the ambient exposure.

And it's used for basically the same reason. The camera doesn't know if it's metering on something that's black, white, or in between. So it will tend to underexpose scenes with bright colors and overexpose predominantly dark scenes. The photographer needs to adjust EC or FEC to account for this.

It makes your Speedlite brighter or dimmer - in situations where you might want more or less flash.

John Sims wrote in post #2256322
It makes your Speedlite brighter or dimmer - in situations where you might want more or less flash.

for example, a fill flash.

So, when would you shoot with it on or off? What situations dictate this?

imhotep wrote in post #2256390
So, when would you shoot with it on or off? What situations dictate this?

Here are a few examples:
1) A dark-skinned person wearing a black tuxedo would need negative FEC, especially if there is nothing else within the range of the flash that will reflect light back through the lens (outdoors or in a room with dark walls).
2) A fair-skinned person in a white wedding gown would need positive FEC, especially if she's standing directly in front of a white wall.
3) If there is something bright in the scene that is closer than your subject, for example if your subject is seated at the opposite end of a table with a white tablecloth, you would need positive FEC to correctly expose your subject, knowing that the white tablecloth in the foreground will be overexposed.

Make sense?

so glad i readthis! very helpful!

Curtis N wrote in post #2256447
Make sense?

Sort of. I'm not 100% clear on what positive/negative FEC means though.

If you are taking a picture a darkskinned person in a dark outfit, wouldn't need more flash? And if the opposite is true (fair skin in white outfit), wouln't you need less additional light?

The advantage of digital is you can suck it and see. I tend to take a shot and then look at the curves and check for any burnt out areas.

If the principal subject is too dark in the image but distant elements (sunset?) are OK the increase the flash (+ FEC). If you are over exposing you principal subject reduce the flash.

imhotep wrote in post #2256636
If you are taking a picture a darkskinned person in a dark outfit, wouldn't need more flash? And if the opposite is true (fair skin in white outfit), wouln't you need less additional light?

Only if you want to make them both 18% gray.

In technical terms, it takes the same amount of light to correctly expose dark subjects and bright subjects. If the bride & groom are standing next to each other in the same picture, you have to choose a single, correct exposure setting and take the shot.

This is why some people like to use manual flash. The power required is calculated based on distance and aperture. The subject's color doesn't enter into the equation.

EC and FEC are not used because subjects of different color (luminance) require different amounts of light. They are used because subjects of different color affect the camera's metering differently. Remember, the camera meters off light reflected from the subject and other elements in the scene. It can't tell the difference between a black tuxedo and a white wedding gown. It only measures the light they reflect. You need EC and/or FEC to compensate for readings from scenes that are significantly above or below average luminance.

That said, the camera's dynamic range sometimes becomes a factor. You can overexpose something black to make it dark gray and bring out the detail in it. By the same token you can underexpose something white to avoid blowing out the detail (God help you if you "correctly expose" the bride's $2,000 gown and she can't see every stitch of embroidery.).

so + to FEC actually dials down the light... and - FEC cranks it up...

i think that is what had me so confused.

Thanks for the help and attention to this thread.

MikeMcL wrote in post #2261306
so + to FEC actually dials down the light... and - FEC cranks it up...

No.

+FEC cranks it up, -FEC dials it down.

I'll try to explain by giving you the camera's perspective. Keep in mind that the main reason for any kind of automatic flash metering is to account for differing subject distances or the light loss from bouncing/diffusing.

You're shooting someone in a black tuxedo outdoors. You hit the button and the preflash fires. The camera measures the light reflecting off the subject and through the lens.

Dark or black subjects reflect very little light. The camera doesn't know it's black. The camera thinks to itself "I got very little light reflecting off the subject from the preflash. The subject must be far away, so I need a lot of light to get proper exposure." So it kicks out a huge burst of flash. Too much, in fact, and your subject is overexposed. The photographer's job (since he knows something the camera doesn't - He is shooting a dark scene!) is to predict this flawed metering and correct with negative FEC for proper exposure.

Now think of the same thing with the white wedding dress scenario. The preflash fires, and the camera thinks "I got a lot of light reflecting off the subject from the preflash. The subject must be very close, so I don't need much light to get proper exposure." So it fires a weak flash, and the subject is underexposed. The photographer's job, again, is to predict this flawed metering and use positive FEC for proper exposure.

This concept applies to any kind of in-camera metering, not just E-TTL flash.

Curtis N wrote in post #2261581
No.

+FEC cranks it up, -FEC dials it down........

Glad you said that. I thought I was loosing the plot there. Nice description BTW.

Excellent mini-tutorial, Curtis! You explained it very clearly and I think even I might have a handle on it! 8)

Curtis, you're amazing. I think I too am finally beginning to "see" the light. Thank you for the real world example & explanation!