In article <4aib8k$pd5@apakabar.cc.columbia.edu>, sridhara@cumbij.bioc.columbia.edu says...
>I bought one of those flash diffusers (a white cube shaped piece of >plastic that snaps onto the flash head) for my 283. (the main purpose >being to create soft effects). (....)

A cheaper solution is a styrofoam cup inverted over the upturned flash
head (advantages: cheap, easy to remove, provides a way to get the
light source above the lens with verticals, reduces the flash output
about a stop [useful for close shooting at wide apertures with fast
films], widens flash coverage to cover fisheye lenses, raises the light source height in horizontal photos without using a bracket).
With either (or any) add-on, there should be no need to compensate
with TTL or Auto mode, just Manual mode.
>>>>))))) BUT! The world is full of hooey, and one bit of hooey is
the business about "diffusing" flash - in most situations, unless
you VERY noticeably change the light source size and/or location,
there will be no difference in the photos when using all these
add-ons that the manufacturers pretend work. "Diffusion" is a myth
- unless there are very close and efficient reflective surfaces for
the wider spread of light to reflect from, virtually all of the
light comes from the flash (and it doesn't matter whether it is "diffused" or not). If you put on a reflector, diffuser, mini-softbox (which just has a hot-spot in the middle of a larger area), etc.,
THERE WILL BE NO DIFFERENCE in the photos at most distances (except
for a loss in flash power, and maybe a broadening in flash angle).
Sorry! If you can (truly) increase the light source size to something
over a foot, you will see a softening of shadow edges for subjects
up to several feet away, but the effect will be very subtle at much greater distances. Try diagramimg the distance and light rays,
(in scale) and you will see why the above is true. If you still don't
believe it, try shooting two identical pictures, one with, one without
the "diffuser". (Then you, too, can laugh at all those press photographers shooting flash outside or in big rooms with their
flashes aimed up with a [little] white card behind...[wasting battery
power].)
Hope this helps.