As 'Lock Exposure' is a time-saving compromise and the locked exposure
not necessarily the ideal exposure for every frame, would it not be
better if 'Lock Film Base Colour' could be set independantly, without
first locking the exposure? This way the base colour could be
accurately determined and locked without being limited to a fixed
exposure for every frame. Or is the relationship between exposure and
film base colour such that varying the exposure make this impossible?

Ricky.

Hello, Stephen Rogers
you wrote...

There are two reasons to use different exposure for different frames of
the same film type:
- The scanner maximum density is lower than the film maximum density
- The scanner produces high noise in the dark parts.

The maximum density of color negative film is relatively low, so point
one shuld be of no concern, at least with a dedicated film scanner
(slide density is far higher than color negative density).

If the scanner has low noise anyway, point two is of no concern, too.
The better way to reduce dark area noise would be a long exposure pass
anyway.

--
Erik Krause
Digital contrast problems: http://www.erik-krause.de/contrast

Hello, Ricky
you wrote...

This can be done, if you scan raw files to disk first (with individual
exposure) and scan from disk then (pro version only).

That depends on your scanner. If the ratio between exposure and film
base color is linear, you can use one film base color setting for
different exposures. But may be, you have to normalize film base color
to prevent clipping. Please read my tutorial (sorry, still draft
only!) at http://www.erik-krause.de/tutorial/part3.htm paragraph 2.
'Scanning without Clipping' for more information.

--
Erik Krause
Digital contrast problems: http://www.erik-krause.de/contrast