To add to Warren's excellent explanation, when you take density range
to power of 10 you get the film range, 10**2.7=500 = 9 stops
(2^^9=512). This again is mapped to an exposure range, which is wider
for negatives and hence have more compression. A scanner is basically
an A/D converter which converts the levels of film intensity into bits.
The difference between bit levels is the quantization error, which
would be seen as a small difference in color from one bit to the next.
Since slide film has less exposure range for similar density range, it
would have more resolution in color separation when scanned, unless of
course you use more bits in the scanner, like 12 bits .vs. 8 bits.
However, the noise will be amplified more with the higher compression
range of negative film compared to slide film.
So, we come back to basic knowledge, if you have a high contrast scene,
negative film will work better, a low contrast scene and slide film is
better; scanned or not scanned.
One thing I have noticed when scanning fuji Reala film, slight
variations in exposure can result in color shifting when scanned
(LS-2000). I have wondered if the 4th layer in Reala makes this film
more difficult to scan? When it does scan correctly, it looks great.
Maybe I don't have it adjusted correctly.
Aside: My folks recently visited and my dad left me with some
ektachrome and kodachrome slides he took in the 1950's (55, 56, 57) for
me to scan. The ektachrome has definitely shifted to the red while the
kodachrome has not. It appears as though the kodachrome has faded and
there is some fungus in places. Is kodachrome more susceptible to
fungas than ektachrome? It will be a challenge to scan and correct
these slides.
Wayne
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