At 16:37 9/1/02, John Gruffydd wrote:
Proper diffused light can only be got from a very large light source.
Covering the flash with tissue does not increase the light source size, so
basically all it does is to decrease the flash guide number.
Incorrect! See remarks below.
(Tissue *is* useful when using direct flash with a wide angle lens that
can't be covered by the basic flash).
A large light source can be got by bouncing the flash from a large surface
or through a large diffuser.
Correct.
Unfortunately the tissue "myth" seems to have been perpetuated like the
idea that focal length affects the perspective - it does not. Only camera
to subject distance affects perspective.
1. The "tissue" is not a "myth." I've used it with decent effectiveness,
albeit quite a number of years ago using a white cotton handkerchief. More
recently I've used the same technique with the 21mm/ND2 white diffusion
panel on a T-32. It has limitations and doesn't work under all
conditions. Using a flat diffusion or ultra-wide angle panel over the
front of a flash head works best with greatest effect in small spaces such
as those found in the average home if it has white, or very nearly white,
ceilings and walls. It does not work well in large, cavernous spaces or
areas with dark walls such as wood paneling. How does it work? It's what
you stated about using bounce. By spreading the light over a very wide
angle, the ratio of direct illumination to that from bounce shifts. More
of it comes from bounce. In smaller spaces with white or very light
colored ceilings and walls, the amount from bounce increases. It's also
why this method has much less effect in large, cavernous spaces or those
with dark ceilings and walls. Used under the proper conditions, it *does*
work.
2. You are quite correct that focal length does not affect perspective,
but you've left out the most important part of managing perspective *using*
focal length. Perspective management is a combination of focal length and
camera position relative to the principal subject. After a decision about
principle subject magnification on the film is made, its perspective is
managed by changing focal length *and* moving camera position
proportionately to maintain the same principle subject magnification.
-- John
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