Even if the ceiling is white it's still not a mirror and will absorb a
lot. Since I have a flash meter I decided to do a little experiment.
Test conditions: Shooting from either 8 feet or 12 feet and measuring
straight-on. Or bouncing off an 8-foot ceiling at the midpoint between
flash and subject. The ceiling is white, unpainted plaster with a brush
textured swirl pattern.
Since the flash was only about 3 feet below the ceiling the additional
distance traveled was not far. By guide number calculations, using
distance only, the additional exposure would be less than one stop. The
measured exposure in both instances, however, was approximately two
stops more for bounce vs straight-on.
I didn't try it but I think if I was angling off both ceiling and wall
as I normally do with indoor TTL shots it would probably require at
least 3 and perhaps 4 stops more exposure.
One slightly disconcerting outcome of this experiment was that I tested
two T-32's and both gave me the same results with the flash meter.
However, both were a full stop below what would have been indicated in
the straight-on shots using guide number instead of the meter. Don't
know why yet.
Chuck Norcutt
Woburn, Massachusetts, USA
Piers Hemy wrote:
> I think that is correct Bill, with the further rider that we assume the
> ceiling is white - if it isn't, you aren't going to get much bounced back.
> Keep in mind that you want to aim the flash so the reflection hits the
> subject. I suggest you either bracket the exposures or get a flash meter!
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