Eh???? Can somebody explain this?

I took 2 photos. One with bounced flash (off the ceiling) and one with direct flash (2 flashes - 420ex and 430ex). The bounced flash photo came out lighter and brighter. See what I mean....

Now can anybody explain this? Taken minutes apart and only the flash orientation was changed.

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No exifs in the pictures...

Anyway, three suggestions

1) direct flash causes specular reflections that may fool the exposure metering slightly

2) In direct flash mode, the metering may take into acount the actual focus distance if the lens reports this back to the camera. Lables on the cups seem fairly well exposed

3) light fallof will make the background underexposed in direct flash mode. Bounced gives a larger light source (possibly at a greater distance from subjet/background) and thus reduces light falloff.

EDIT: I see now that you are using two flashes. I assume in ETTL mode. In this case, point 2 is probably not an issue here...

Looking a bit closer at the lables, they seem to be roughly equally exposed in both pictures, so assuming that this is what you wanted to be exposed properly, both direct and bounced give similar results.

The differences in the picture can then be attributed to different light qualities, direct flash gives a strong light fall off and is more sensitive to the orientation of surfaces. eg, the paper in direct flash is almost parallell to the light sources and is thus not well illuminated (underexposed) despite being closer to the light sources than the cups.

lederK wrote in post #4657897
1) direct flash causes specular reflections that may fool the exposure metering slightly.

That would be my first guess.

lederK wrote in post #4657897
No exifs in the pictures...

Anyway, three suggestions

1) direct flash causes specular reflections that may fool the exposure metering slightly

2) In direct flash mode, the metering may take into acount the actual focus distance if the lens reports this back to the camera. Lables on the cups seem fairly well exposed

3) light fallof will make the background underexposed in direct flash mode. Bounced gives a larger light source (possibly at a greater distance from subjet/background) and thus reduces light falloff.

EDIT: I see now that you are using two flashes. I assume in ETTL mode. In this case, point 2 is probably not an issue here...

And this would be my explanation (and isn't a guess, either )

With direct lighting the distance from the light to the plastic cups is much shorter than to the background relative to each other.

When the light is bounced off the ceiling, the light to cup distance and the light to background distance are relatively the same and hence the equal lighting of both.

rhys, after carefully examining both pictures, my advice is DON'T DRINK THE WATER!!!

j/k
Mike

MT Stringer wrote in post #4658312
rhys, after carefully examining both pictures, my advice is DON'T DRINK THE WATER!!!

Too late.... I drank it in a moment of thoughtlessness and was in absolute agony for a few hours. Then when I came to I found I'd changed gender while I'd been unconscious... That's when I started having cramps too - lol.

The only things I can think of are:
1. The camera is metering off the reflections in direct flash mode and off the scene in bounce flash mode.
2. The direct flash is producing a specific illumination that's illuminating only the front of the scene and the bounce is illuminating all of the scene. (this doesn't make sense though when light travels so darned fast!)

Leo is right, but I'm not wrong.
The "5 days" sheet of paper is still brighter in the bounced shot, and it's closest to the lights.

Curtis N wrote in post #4658362
Leo is right, but I'm not wrong.
The "5 days" sheet of paper is still brighter in the bounced shot, and it's closest to the lights.

Yes, but have you considered the placement of the flash and the angle at which the light is hitting that piece of paper? His flashes are set too low. IIRC, the same comment was made about his ginger bread house picture, too.

Curtis N wrote in post #4658362
Leo is right, but I'm not wrong.
The "5 days" sheet of paper is still brighter in the bounced shot, and it's closest to the lights.

Well, as I wrote earlier, this is expected due to the large angle between the incident light onto the paper and the normal direction of its surface. The light only graces the paper surface and thus the the incident light intensity over the surface is low.

Curtis N wrote in post #4658362
Leo is right, but I'm not wrong.
The "5 days" sheet of paper is still brighter in the bounced shot, and it's closest to the lights.

That's probably because the flashes were on their little feet, two feet away from the 5 Days sheet and standing on the table. Thus the sheet was probably not quite in the direct flash illumination path. Here's a photo of the flash setup...

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PacAce wrote in post #4658222
And this would be my explanation (and isn't a guess, either )

With direct lighting the distance from the light to the plastic cups is much shorter than to the background relative to each other.

When the light is bounced off the ceiling, the light to cup distance and the light to background distance are relatively the same and hence the equal lighting of both.

Agree. (Let us assume camera to subject =8', camera to b/g = 16'; and indirect flash aimed upward about 45 degrees from camera 4' above floor to items about 4' above floor.)

Direct: falloff of light due to Inverse Square = -2EV from 8' to 16' (f/8 to f/16 is -2EV)

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)

...therefore bounce light results in less distance fall-off to the background items

Agree here, too. The white paper is brighter in the bounced light photo simply because of the angle of incidence of the light striking the paper; the light is much more at an acute angle to the paper surface and little comes back to the lens, compared to the more perpendicular angle from the bounce allowing more light to be reflected back to the lens.

Camera to subject 4 feet. Camera to background 7 feet. Flashes to subject 18". Ceiling 7'.

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.