Hi all,

I've read up on RA-4 optical printing recently; haven't had the chance to try it yet for lack of chemicals but I hope to change that in the next couple of months and get my colour process all at-home and analogue. However, I have some questions about achieving correct colour balance and how is that even possible with a single adjustment of the enlarger light-colour?

Compare it to making a scan, where I pick RGB values for both the black- and white-points, thereby changing the colour balance independently for the low and high values in the image. That means I can correct for any mask colour as well as any lighting conditions that the image might have been exposed with.

Now consider what happens with RA-4; say the (daylight) film was exposed in daylight. You correctly set the enlarger colour and that will result in neutral shadows and highlights, the mask correctly cancels out and everyone is happy. Now what happens when I expose the film under tungsten light? I can dial in a bunch more Y and some M to neutralise the image, but won't it mean I can neutralise either the shadows or the highlights but not both?

Perhaps I am overthinking this or I'm confused about how the colour mask works; is it actually possible to correct for arbitrary lighting conditions (assuming continuous spectrum, nothing truly nasty) while printing?

Or must I do all the corrections pre-exposure, just as one would with chromes? Because that would really suck; I can do the colour corrections in a hybrid process but would like the resolution obtainable from optical printing, not to mention a desire to control/implement everything possible myself and that there are images I'd prefer not to send to a lab.