Struan, so you're suggesting taking 3 exposures with 3 filters successively? That is very interesting and completely new to me. I know that Ives did something similar, but this was with separation negatives and a screen w/ 1/3 of the surface transparent, which was shifted by thirds for the successive, filtered exposures.

The 3 filter idea makes sense though, and I thank you for mentioning it! I have a handful of Wratten filters, one of which is "deep blue monochromat". I suspect that this kind of narrowband filter would be ideal, though the exposures would of course we epicly long.

Very cool...