Eh???? Can somebody explain this?

Looking at the foreground paper and the flash position, could it be that the paper was beyond the angle of the flash? I was using something like 50mm to concentrate solely on the glasses and the paper. Does the flash zoom head work when it's off camera?

Curtis N wrote in post #4658855
I understand why the paper is brighter in the bounced shot, relative to the rest of the image.

But E-TTL doesn't know or care where the light is coming from. It's just measuring what gets reflected. And E-TTL exposed both the foreground and the background of the bounced shot brighter than the direct flash shot. The differences in overall exposure between these two shots is much more dramatic than the relative differences within each image.

There is a reason that E-TTL underexposed both the foreground and the background with direct flash, and my money is still on the specular highlights in the glasses.

I agree. I had this same problem the other day when I was photographing some people in front of a wall with a picture frame. I was bouncing flash off the ceiling and using a bounce card. The light from the bounce card reflected directly off of the picture frame and caused E-TTL to underexpose the flash exposure.

Do you think changing the metering would be any help? I notice the camera was on centre-weighted average. It's so hard to tell what these metering symbols mean on the display. I'm all for dumping symbols and getting text messages - so much clearer. Pity the idiots at Canon don't think so.

The camera's ambient metering mode doesn't matter. The flash metering mode probably will have an effect, if my theory is correct.

Try switching from Evaluative to Average E-TTL metering (via custom function on the camera).

Wilt wrote in post #4658692
Indirect: falloff of light due to Inverse Square = -1EV (light bounces and travels 11' to subject, light bounces and travels 16' to background items (f/11 to f/16 is -1EV)

To nitpick: not quite. inverse square law only applies to point sources of light (ie those that give harsh shadows). Bouncing light creates a limited surface source of light and the falloff depends (roughly) on the relation distance/(radius of light source).

At: source radius>>distance -> almost no light fallof
At: source radius<<distance -> inverse square

/lk

This IS a very interesting thing!

More data:
Camera - XT
Lens - 17-85 IS
Focal length 50mm.
Shutter speed 1/200th
Aperture f8 in pic 2 (I did that because I was bouncing off the ceiling and knew that the flash power would be vastly reduced)
Aperture f14 on the first picture.

lederK wrote in post #4659138
To nitpick: not quite. inverse square law only applies to point sources of light (ie those that give harsh shadows). Bouncing light creates a limited surface source of light and the falloff depends (roughly) on the relation distance/(radius of light source).

At: source radius>>distance -> almost no light fallof
At: source radius<<distance -> inverse square

/lk

Not disputing what you state, as I know this is true. But it seems to overly complicate the topic of lighting far beyond what the majority on POTN are ready for!

In the bounce example, the foreground is indeed a bit brighter than the background area, so I'm sticking to my oversimplified explanation for now!

Curtis N wrote in post #4658855
I understand why the paper is brighter in the bounced shot, relative to the rest of the image.

But E-TTL doesn't know or care where the light is coming from. It's just measuring what gets reflected. And E-TTL exposed both the foreground and the background of the bounced shot brighter than the direct flash shot. The differences in overall exposure between these two shots is much more dramatic than the relative differences within each image.

There is a reason that E-TTL underexposed both the foreground and the background with direct flash, and my money is still on the specular highlights in the glasses.

I agree with your analysis about the relative underexposure of the direct flash.

rhys wrote in post #4659053
I'm all for dumping symbols and getting text messages - so much clearer. Pity the idiots at Canon don't think so.

But not everyone reads English and it so greatly complicates product design when they have to incorporate language selection! Symbols can be universal, but they are hard to select, in a lot of cases, to be intuitive!

Wilt wrote in post #4659793
I agree with your analysis about the relative underexposure of the direct flash.

I tend to agree. I had this problem at a wedding. I reckon direct flash needs +1 EV

Wilt wrote in post #4659813
But not everyone reads English and it so greatly complicates product design when they have to incorporate language selection! Symbols can be universal, but they are hard to select, in a lot of cases, to be intuitive!

They have language selection anyway - might as well make it worthwhile.

Rhys when you changed aperture the flashes realise this and adjust there output accordingly so that shouldn't be a factor. I'm with curtis and think the reflections off the cups have fooled the ETTL into underexposing.

Welby wrote in post #4660172
Rhys when you changed aperture the flashes realise this and adjust there output accordingly so that shouldn't be a factor. I'm with curtis and think the reflections off the cups have fooled the ETTL into underexposing.

Oh I'm not disagreeing that the flash knew the aperture had been changed. As I said, I changed the aperture only in order to allow for the extra distance - flash - ceiling - subject and to allow for absorbtion of the light by the ceiling.

I tend to agree that reflections could have fooled the flash but check this out... Why have I got the same issue with dark images here - I had to give this a +2 ev in DPP to get it to look somewhat reasonable.

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Curtis N wrote in post #4658855
I understand why the paper is brighter in the bounced shot, relative to the rest of the image.

But E-TTL doesn't know or care where the light is coming from. It's just measuring what gets reflected. And E-TTL exposed both the foreground and the background of the bounced shot brighter than the direct flash shot. The differences in overall exposure between these two shots is much more dramatic than the relative differences within each image.

There is a reason that E-TTL underexposed both the foreground and the background with direct flash, and my money is still on the specular highlights in the glasses.

Curtis, I'm not disputing the fact that the specular highlight caused the subject to be slightly underexposed compared to the image shot with the bounce flash. However, is that what really made the bounced picture look brighter? Or is it the fact that the background is lit up very well, just like the forground, as well as the fact that the foreground is more evenly lit by the bounced light, that makes the image look brighter? Wasn't that what rhys was asking, "why the bounced flash picture looks brighter than the direct flash picture"?

Looking at it again, I wonder whether the bounced picture just has more even illumination.

rhys wrote in post #4660321
Oh I'm not disagreeing that the flash knew the aperture had been changed. As I said, I changed the aperture only in order to allow for the extra distance - flash - ceiling - subject and to allow for absorbtion of the light by the ceiling.

I tend to agree that reflections could have fooled the flash but check this out... Why have I got the same issue with dark images here - I had to give this a +2 ev in DPP to get it to look somewhat reasonable.

That's because most of the subject is white so the flash is going to underexpose as should be expected unless you use +FEC.