In article <425blf$mme@net.auckland.ac.nz>, boonl@ccu1.auckland.ac.nz says...
>I have an inflatable softbox and IMHO the light coming out of
>it is still as harsh as if it was not there.
>Now, I am thinking of getting an umbrella to diffuse the
>light coming from the flash. What I need to know is how the
>size of the umbrella influence the coverage and level of
>diffusion.
>Also, can similar effect be obtained by using one of those
>attachment placed on the head of the flash to bounce the
>light? It just looked to small to give a good area coverage.

I am not a believer in the existence of "diffused light", at least
when it comes to the influence of a "diffuser" on a compact flash
on the softness of shadows. The softness of a shadow (edge) is
related to the size of the light source (an umbrella can sure help
here, or a bounce off a wall or ceiling), the distance of the
light source from the subject, and the distance of the subject
from the surface on which the shadow is cast. Adding a "diffuser"
to a small light source that does not significantly enlarge the
light source does little (everything else being equal) except
reduce flash efficiency (and increase the angle of coverage of
the flash - useful for super-wide lenses). The extra light
reflected off surrounding surfaces back to the subject is
generally too weak relative to the direct light from the flash
to have much effect. When the flash is used where there can be no
reflections (like outdoors), "diffusion" is clearly useless.
(I wonder how many batteries could have been saved if people
realized how little effect the little white card taped behind the
head of almost every news photographer's flash has [except on
recycle time and flash reach].) A quick test to get an idea if
a new flash add-on doo-dad is going to help (though it is a little
hard on the eyes), is to point the flash with and without the
add-on device at yourself at arms length, fire the flash, and
compare the sizes of the afterimages. You may be surprised to
see roughly equal size afterimages from the flash alone, and
with the many mini "softboxes", reflectors, etc. that are foisted
on us poor photographers.... In order for softboxes and reflectors
to work, there needs to be sufficient distance between the light
source and the "diffuser" or reflector for the transmitted or
reflected light to become a much larger light source than the
original flash alone.
Hope this helps.