I made a quick test a couple of days ago, just photographing a projected 6x7 Velvia. I have published CCD and drum scans of the same slide on this thread.
I don't know what I think...
Putting the image on the light table and using a macro lens would give a better result. Although using a glass mount for the slide (GP) film flatness is an issue in projection.
I can post raw images later this week if anyone is interested.
I had an interesting chat with an engineer with a motion picture scanning company.
He told me that macro lenses just don't do the job well enough and to approach the qualities
of a drum scanner systems have to do three flash exposures and need to be heavily built systems
with precision thermal/humidity control and custom optics as well as 4 edge frame pressure plate.
In his opinion a repro stand with a still camera and macro lens however high end will only
be a high volume, but low quality scanning alternative. Great for volume documentation, but not a high
image quality system.
Some customized systems use dichroic filters and 9 monochrome exposures. Doing color balance analogically before
digitizing makes a significant difference.
Well it's back to scanners.