Flash and exposure

[wintoid]

OK I've got a question, and I have an example image which you can see at http://simon.pietroni.co.uk/exposure_question.jpg

This image was shot indoors using a 300d with a 24-85 lens and a 550ex flashgun bounced off a low ceiling. The EXIF information looks like this:

ISO 100
Shutter 1/100
Aperture f10.0
Flash exposure compensation +2.0
Focal length 85mm (on a 24-85mm zoom)
C1 claims it was shutter priority, but in fact it was shot in manual mode

(incidentally I typed all the EXIF info manually, is there some way to extract it from the image in a "pastable" format?).

Now, to get this image to look as bright as it does, I had to use FEC +2.0 and also dial in 2.15 exposure compensation in C1SE. This sort of thing ALWAYS happens to me with the 24-85mm zoom, and almost never happens with my 50mm 1.4 prime at similar settings.

So my question is this... my flashgun obviously completely failed to generate enough light at f10 1/100s, and only with 4 EVs of adjustment (is that the right term?) was the image bright enough. What have I done wrong? Is it just that f10 1/100s doesn't let much light in and this is to be expected? It seemed to me that my target (my daughter Katie) was close enough to be reasonably lit even with a small aperture.

Any advice would be gratefully appreciated!

[scottbergerphoto]

At f/10, you have reduced the effective distance of your flash to 55/10=5.5M or about 15 feet.
Distance = GN/F stop
When you bounce off the ceiling you have to add the distance to the ceiling and from the ceiling to your subject. You also lose light due to the diffusion off the ceiling and the fact that the flash head doesn't zoom in bounce position. You are exceeding the capacity of your flash. You need to use a wider aperture or a higher Iso or both. If you increase the Iso to 200, the distance will increase by 1.4X and if you go to 400 by 2X.
Regards,
Scott

[wintoid]

Thanks for that info Scott. Considering you say that I was exceeding the capacity of the flash, would you say that the +2 FEC I dialled in probably didn't actually do anything, because the flash was already firing at full power?

I just went and set up a shot of a cuddly toy at the same spot as the example I posted, and shot it with the 24-85mm and the 50mm using the same settings, and actually it was about as bright with both lenses, so that was obviously a misconception of mine. However, I did try removing the skylight filter from the 24-85mm and found that the image became noticeably brighter.