+EC -FEC - advanced question

HI all, looking though the posts and knowing my manual pretty good by now, I have specific questions on FEC when combines with EC. Do these two interact the same way in different shooting modes. I will describe an example.

shooting outdoors in AV mode, I dial in +EC by a full stop ( let`s say ). I know the background is well exposed already but I also know that canon in AV mode with flash on will purposely underexpose the background because it is smart enough to know that the subject is already potentially well lit and that the flash will overexpose the subject if metering for ambient light. Also, as many have stated, canon purposely wants your subject to stand out. So now, I have offset this.

before I ask about the FEC, I have to make an inquiry here that I have not seen addressed, at this point my guess is the subject may overexpose. Even though increasing EC should affect ambient background according to some, the foreground will be exposed longer at the same flash output. ( This is assuming a constant f/ due to AV mode) I am not so clear on whether the flash will output less now simply because I +1 EC. I may be wrong, after all, the camera will still fire the preflash, and who knows if it is smart enough to compensate for a proper subject exposure after my +1 EC. So the question here is, will it fire a lesser flash to offset what I have done.

What will happen to the pic if I dial in -FEC a full stop now. Which brings me to the main question. In p mode with all the same steps as above, does the camera behave the same way ?

After all that, I am sorry if it doesn`t read nicely, here is a clear re-cap

1. Will the camera lower flash output when I dial in +EC in AV mode ?
2. Will the camera act the same in p, tv, and AV for the above setting ?

Too advanced for me, sorry !
Try here for more insight

http://photonotes.org/​articles/eos-flash/#faq7

Thx, I have read that, it is great info, but does not address this. I may eventually do some trial and error, and can then post the findings, but I have a feeling there are some here who may know from experience.

You didn't say which camera. E-TTL and E-TTL II behave slightly differently.

I'm going to assume that you are referring to an E-TTL II camera.

AMG wrote in post #3108948
canon in AV mode with flash on will purposely underexpose the background because it is smart enough to know that the subject is already potentially well lit and that the flash will overexpose the subject if metering for ambient light.

I have heard this a number of times, but I have never seen anything in any Canon literature that I've looked at which states this. I believe that it mostly is a misunderstanding of Canon's "Auto Fill Flash Reduction" feature. That feature reduces FEC, not EC.

To my knowledge there is no automatic reduction of ambient exposure when flash is active. Other people believe otherwise, at least for the original E-TTL on 35mm film SLRs. You can certainly test this easily enough, as in this test on a 20D (E-TTL II) which claims to have found such effects at lower light levels regardless of flash exposure mode.

Correct. If you are shooting with Evaluative flash metering (not the same as Evaluative exposure metering), the camera will automatically reduce the flash exposure if the ambient is bright. If you are shooting with Average flash metering, or are using Flash Exposure Lock, then you must reduce FEC yourself.

Note: some early discussions claimed that Auto Fill Flash Reduction was not present at all in E-TTL II. This early information appears to have been incorrect, although AFFR is now restricted to Evaluative flash metering in E-TTL II. (I cannot claim that this statement is definitive, but it is correct to the best of my knowledge.)

Flash exposure is determined by firing a preflash and examining the results. It is unrelated to the ambient exposure settings, aside from the possibility that the flash will be operating in FP Sync mode.

The actual flash duration will automatically be adjusted for the difference between the aperture at metering time (wide open) and the aperture at exposure time, so if EC affects aperture (Tv or P mode) the flash duration will change with EC. But this still does not affect the total flash exposure unless the duration becomes too long or too short to execute properly.

Not because of EC. It will reduce the flash if you are using Evaluative flash metering and the ambient is bright enough.

You'll get one stop less flash than you would have had.

The primary difference in P mode is that the camera will not let the shutter speed drop below 1/60 second. In dim light, you will not get a full exposure off of the ambient light, and the flash becomes the main source of lighting for the scene.

And, of course, in P mode you lose control of the aperture setting. In dim light the camera will keep the lens wide open, giving maximum flash range but sacrificing depth of field and possibly sharpness. In bright light the camera will stop the lens way down, possibly making your subject be beyond the range of the fill flash.

It depends on how you are adjusting EC. If you are using Av mode, then you Adjust the aperture up and down, and the camera sets the shutter speed either according to the ambient light or at a fixed 1/200 based on what you set for Custom Function 03. By adjusting the aperture, you are changing the output of the flash too with ETTL II. The camera will do it automatically. If the flash exposure is not bright enough, then Increase the FEC and it will raise the flash exposure, but not the ambient. For best results with flash/ambient exposure, use Manual Mode. This way you can adjust your ambient to your liking with the Shutter speed and your flash exposure with the FEC. Depending on the Aperture you use will determine if the flash can handle it. Some small flashes can't handle extremely small apertures. They just don't have enough output. If thats the case, Increase your ISO. I try to work in ISO 100 anytime I can.

thx guys, yes, Doug, that was a very detailed response that I may need to read a couple of times - I realize now the info I forgot to include, my bad, sorry.

I am using a rebel XT and the speedlight 420 which has Hi-speed sync, so...

my opening is set to maximum by me at 4.5. I take a shot with no adjustments to EC or FEC - then I dial in +1/3 EC for shot 2, the shutterspeed will decrease by one setting obviously, but will flash output change ? This assumes exact same composition and backgrounds for both shots.
what I was not clear on is whether the flash output would be the same as the first shot if no EC is dialed in.

shot 1 and shot 2 will have a differently exposed backgrouds now, but will the subject be exposed differently too or will the flash output less on shot #2 to try and compensate for longer exposure time due to EC+1/3, and therefore produce a subject equal to the first shot

btw - I guess the rebel XT is ETTL 2.

AMG wrote in post #3108948
I also know that canon in AV mode with flash on will purposely underexpose the background because it is smart enough to know that the subject is already potentially well lit and that the flash will overexpose the subject if metering for ambient light.

From what I have read, (See Doug Pardee's link above) NEVEC (negative evaluative exposure compensation) only kicks in at relatively low light levels and is generally not an issue in outdoor daytime conditions. You'll get the same ambient exposure outdoors, with or without flash. The NEVEC behavior is the same in Av, Tv and P modes, according to the aforementioned article.

I also concur with Doug's summary of automatic fill flash reduction. With E-TTL II, the flash exposure is automatically reduced to avoid subject blowout in Evaluative E-TTL mode, but not Average E-TTL. I base this only on personal experience, not official documentation.

Common sense tells me this: In sunny conditions, a human subject will have hot spots and shadows. The exposure of the hot spots will be at or near the high end of the camera's dynamic range, even without flash. If you simply add light with flash, you will blow out these areas. So in sunny conditions I normally dial in some negative EC (anywhere from -1/3 to -1) to give me room for added flash exposure without creating bad blowouts.

In cloudy conditions, the subject will normally have much less contrast in ambient light, and I can keep EC at zero. Adding flash will give the subject a bit of "pop" without significant risk of bad overexposure.

I normally use Evaluative E-TTL mode for outdoor fill, with a bit of negative FEC (-2/3, give or take).

There are no "standard" settings that always work well, because both the ambient and flash exposures are influenced by subject & background luminance (white wedding gowns, black tuxedos, sand, snow, etc.

EC and FEC are not dependent on each other because flash varies much with subject distance, focal length, and subject brightness. So using EC -1 and FEC +1 doesn't mean you'll get a properly exposed image.

P mode is too much of an auto mode and flash will almost always be used with 1/60 which is ok for people trying to stand still but it won't cut it for kids that move quick and can't stand still.

You're really best to learn flash in M mode for indoor work ignoring your light meter, and use it as a fill flash in Av mode where you meter for ambient light (and common settings can be EC -1 and a FEC that gives a good result) and use the flash to illuminate your subject and fill in the shadows.

I always use AV outdoors, but for indoors, I am not sure how to work. My daughter`s party in on sunday, and I will be renting a lens. I guess I would really like to use no flash, but I don`t know if that is best, I will have to try before the party.

AMG wrote in post #3112581
for indoors, I am not sure how to work. My daughter`s party in on sunday, and I will be renting a lens.

Where is the party? In residential settings, the easiest way to get good shots is to put the camera in manual mode, ignore the ambient light and bounce the flash.

Doug Pardee wrote in post #3109281
To my knowledge there is no automatic reduction of ambient exposure when flash is active. Other people believe otherwise, at least for the original E-TTL on 35mm film SLRs. You can certainly test this easily enough, as in this test on a 20D (E-TTL II) which claims to have found such effects at lower light levels regardless of flash exposure mode.

So, taking my own advice, I tested it on my XT/350D (E-TTL II). What I found is that in low light, the ambient exposure is indeed reduced by one stop provided that the ambient metering mode is Evaluative. There is no reduction when using CWA or Partial metering modes for the ambient. So my conclusion (based on not nearly sufficient testing) is that on E-TTL II, NEVEC will apply negative EC in dim light but only when using Evaluative metering mode, and AFFR will apply negative FEC in bright light but only when using Evaluative flash mode.

Which makes a kind of sense, if I think about it. If you're not using Evaluative mode (ambient or flash as appropriate), the camera figures that you don't want it messing with your numbers. Otherwise, the camera reduces either the flash or the ambient exposure, whichever is already expected to produce less brightness. There may also be a region of ambient brightness (around Ev 10) where both are partially reduced.

Doug, could you be so kind as to broaden your explanaton of this. I am scared that without evaluative metering, the background would be come too underexposed, id this correct ?

BTW, the ceilings were way high so impossible to bounce flash. I believe I ended up using AV mode, which allowed me at least to try and balance background ambient exposure and subject, I believe I dialed in a full stop +EC, and then I fooled around with -FEC, sometimes leaving it at 0, sometimes -1/3, and -2/3. Couldnt see a difference, it seemed the flash fired less anyway due the +EC. here is a link to some pics that we shared if you would like to see, in the end, I had to rent a 17-35, because the others we already taken. I use a 420, and an XT. I do notwish to see any edits in this case, but any comments are always welcome. Of coarse, keep in mind, I was trying to participcate as well, so preparation for each shot was non-existent. I looked for a balance between being able to take a shot with as little preparation as possible, with as much control as possible.

here is link

http://new.photos.yaho​o.com …w--&ts=1177976487&.src=ph

AMG,

Those shots are exposed quite nicely for the most part. Ambient seems to be the predominant light source, which is what I would expect with +EC and -FEC. But the flash probably made a huge difference in the backlit shots like IMG_0946. It looks like you had plenty of light there from those big windows. This is always nice to have, and using flash helps brighten up your subjects when you're shooting from the dark side of the room.

As a group, they might be better with a little less ambient and a little more flash, but not much.

yes, the flash did help, but there was some work in raw conversion to boost some of the curve to better expose the subjects, that is an example of a shot that had I used center weighted or p mode in general may have provided a better starting image, but I did not have the luxury of changing settings between shots, so I am happy that they at least had enough exposere to play with in conversion.

AMG wrote in post #3144924
Doug, could you be so kind as to broaden your explanaton of this.

I'm not sure what more I can add. The use of supplemental lighting in concert with ambient lighting is an entire photographic discipline in itself. Learning to control lighting well is, in my opinion, a whole lot more challenging than learning all of the other SLR stuff (exposure, focal length, depth of field, etc.) put together. And it doesn't happen to be my area of expertise.

I don't understand your concern. Just try different things and see what works for you. One of the great things about digital is that you can take all sorts of test pictures virtually for free, and you get immediate feedback from them.

In my experiment on my XT, using evaluative (ambient) metering in relatively dim light with flash resulted in the background being exposed 1 stop darker than it would have been with CWA or Partial (ambient) metering. The camera did this apparently because it expected the flash to provide the bulk of the lighting, and didn't want to overexpose the subject by using too much ambient.