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This is a real dilemma - they

This is a real dilemma - they could make two sensor types, one with narrow-bandpass colour filters, one with broad spectrum RGB. You would end up with a low ISO sensor offering maximum colour discrimination and Delta-E accuracy (but of course the potential for greater Delta-E errors if software conversion was not precisely matched to the transmission curves); and a high ISO sensor where the overlapping curves could reduce colour discrimination, relying on software to restore it.

I always felt that the RGB filters used on the KM7D/5D were narrower in band than the filters used on the same sensor by Nikon (D70 etc), allowing the lower ISO 100 setting and also giving the distinctive colour of the 7D/5D. I have also always thought that Canon's (early) RGB filters must be weak, helping reduce noise but giving a colour quality I never liked as much. The wide gamut captured by Canon models compared to the 7D/5D also points to this - narrow cut filters will, of course, limit the overall gamut but improve discrimination and accuracy within that gamut.

Did you mean green and blue are perfectly balanced in tungsten light, not green and red?

I have a large stock of ex-Minolta 85B (daylight to tungsten) conversion filters here, never been able to sell them. I gave away 200 40.5mm ones last week (40.5mm is not much use!). I may try the 85B in daylight, using the camera's tungsten preset, to see if it has some benefits.

David