Colour / exposure limitations of negative / slide scanners

[Adder]

At the mo I'm scanning a pile of negatives and slides using a HP 4470c
scanner with the HP XPA adaptor for slides and negs

black and white negs look good, no exposure adjustments needed, clear and
sharp

colour slides need the highlights increased by 100. darker slides are a
lot more difficult, midtones also need increasing, the result is not as
good.

colour negs can scan pretty well at the same settings as black and white
negs, but with a greenish cast.

I remember seeing slides that other people had scanned on scanners, it
seems to be very difficult to get a good slide scan

assuming here there are known limitations for colour scanning with
domestic gear, like maybe the lightsource is not white enough or the CCD
just doesn't respond linearly? any clues?

 

[Jim]

At the mo I'm scanning a pile of negatives and slides using a HP 4470c
scanner with the HP XPA adaptor for slides and negs

black and white negs look good, no exposure adjustments needed, clear and
sharp

colour slides need the highlights increased by 100. darker slides are a
lot more difficult, midtones also need increasing, the result is not as
good.

I have scanned lots and lots of slides. It is rare indeed to find one that
doesn't need some minor adjustments.
Which emulsions are you scanning. Not all slides keep well.

colour negs can scan pretty well at the same settings as black and white
negs, but with a greenish cast.

The greenish cast usually comes from fade. Especially bad ones for such are
all Kodak negative films between Kodacolor II and Gold (except Ektar).

I remember seeing slides that other people had scanned on scanners, it
seems to be very difficult to get a good slide scan

Not for me, but I don't use the HP scanner

assuming here there are known limitations for colour scanning with
domestic gear, like maybe the lightsource is not white enough or the CCD
just doesn't respond linearly? any clues?

That is a rash assumption. There are simply too many variables to make such
an assertion. The causes could range from poor profiles, inadequate
scanners, and poor emulsion types.
Jim