"whisky-dave" wrote in message
...
So what is the advantage of RAW, and what is the equivalent in film.

It is very approximately the equivalent to going back to the negative and
printing it at a different exposure or with different colour-correction
filters so you map a different part of the wide exposure latitude of the
negative onto the more restricted latitude of the print. Many automatic
printmaking shops have their machine set to clip the brightest 5% of the
print (the darkest part of the neg) to white and the darkest 5% to black
(thus losing detail at those two extremes) because this produces more
contrasty, less muddy prints.

For digital, some cameras are set to do the same sort of thing when going
from the sensor image to the JPG, as well as to apply some sharpening and
JPG compression, whereas AFAIK the raw file is not lossy compressed, is not
sharpened and often doesn't have any white balance correction; you are left
to do all those things to your own preference using proprietary RAW -
JPG/TIFF/PNG software that comes with the camera or with packages such as
Photoshop which can read various cameras' RAW formats. Some cameras' RAW
files actually have the suffix DNG (digital negative) because that is
effectively what the file is - what the sensor saw before any in-camera
corrections.

My SLR
does and I have set it to take both JPG and RAW for every photo. I
still
underexpose by 1/3 stop on both cameras for the benefit of the JPG, but
I don't think it affects the RAW (I could be wrong on that).

It should affect both but 1/3 of a stop isn't really much unless you are
on the limit.

a 1/3rd of a stop surely with digital this should be expressed as 0.33333
of a stop and what is a stop in digital terms ;-)

As with film photography, 1 stop is a halving/doubling of the amount of
light getting through the lens (eg f 5.6 - f8) or a halving/doubling of the
shutter speed. Maybe 1/3 stop should be expressed as 0.33 recurring, as you
say :-)