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As an adjunct to the Tangents blog, the intention with this forum is to answer any questions, and allow a diverse discussion of topics related photography. With that, see it as an open invitation to just climb in and start threads and to respond to any threads.
On camera bouncing from far away walls using high ISO
I started a thread on DPR posting a picture where I used a wall that was about 30 feet away to create directional light on my subject on a very overcast afternoon. I'm pretty sure the flash did what I asked it to do but other posters questioned it and it's been suggested that the flash did not contribute to the exposure.
The subject is my wife and I think I know how my wife look under flat lighting

I purposely chose F2.8 @ ISO3200 to max the range of my flash. I wanted to get some reassurance as to wether I did the right thing and the flash did in fact contribute to the light pattern on my subject. I think there's no better place to ask than here

FWIW here's a link to the thread:
http://forums.dpreview.com/forums/readflat.asp?forum=1025&message=37372358
Comments
Your final image seems to have turned out fine in any case.
I shoot action sports with fill flash at ISO 3200 at ranges in excess of 60 feet quite often, mostly to keep better, more consistent skin tones and WB under field lights and battle the rainbow color effects of lights cycling in many HS gyms ... both bounced and direct.
Here is an example of two frames from the same series where on the left, the first frame of the series, has noticeable fill, and on the right, the last frame of the series, received no flash as the flash had not fully recycled ... the difference is subtle ... but noticeable ...
http://www.butchmiller.com/forum/FP_Fill.jpg
Here's an earlier thread, where I bounced flash off a wall outside. The wall was about 5 car lengths away, and the bounce flash does make a difference.
http://neilvn.com/tangents/2009/05/15/high-iso-is-no-substitute-for-good-light/
It isn't the greatest photo, but it does show the difference.
Here is another thread with a relevant image.
I bounced the flash off a far wall inside a museum.
http://neilvn.com/tangents/2008/07/11/a-light-touch/
I couldnt tell you the first thing about light physics and know very little inverse square whatever. Truth is....dont care. I cant think of this in middle of session. Just have to call on experience and understanding camera settings and how they work together.
Just happen to know from experience that at 2.8 and ISO 3200...flash goes a looooong way.
I also know, that wont work at ISO800. I also know it wont even work at ISO3200 and say f5.6. It the combo that made it possible. You can pick up flash from one endzone to the other on football field at ISO3200 and say f1.8 or f1.4.
Dont cut yourself too short, just that you may have never tried those settings and bouncing from walls that far. I have cause you get in a pinch and you'd bounce off anything.
I bounced off a group of 4 people wearing very light cloths once in an open field.
Just asked, stand here and close your eyes, this is gonna be bright. But it worked.
So no, you dont need to learn more light physics....just grab your camera and see what works.
The average top of the line hot shoe flash units have a Guide Number of 100-120 ... This should give you settings in the neighborhood of f/11 at a distance of 10 feet at ISO 100 when using direct flash firing at full power ... So bouncing a total distance of 60 feet at ISO 3200 is well within the output capabilities of the flash including factoring in the reflective efficiency of the surface you are using to bounce the light.
I just noticed this post from 2011, AGC1976 the fill flash did exactly what you wanted it to do, look at the catch light in her eyes.
Quin