Positive About Negatives: Using Filters with Redscale #1

I must start by saying I do not shoot a ton with redscales. But when I do, I mostly treat the film as BW stock - searching visually strong shapes and striking architectures to complement the effect making it monochrome like. I like the strong red tone that redscaled Ektar gives - almost a post apocalyptic look. However I was bored of shooting contrasty photos with heavy orangy/red tones and wanted to do something different this time.

You may notice some scratches in the images - I attribute this to the fact that redscale film is running through the camera backwards and is easily scratched. Also saw some uneven development marks - could be a development time issue due to lack of consistent agitation. But it gives an interesting look to the photos and I don't really mind them. I could have fixed in post but chose not to.

Nikon F3 w/ 50mm 1.4 Nikkor

This time I wanted to experiment with the Blue filter and shot a few using that as well - and the only 35mm camera with a blue filter on it was my favorite 35mm the Nikon F3.

It was great timing to get the hand-rolled Redscale for this shoot, from Denise - I was planning to overexpose 3-5 stops to really get the subtle brown/orange tones and was planning to roll my own Kodak Gold 400. Denise saved me some work!

This time I was experimenting with the Blue 80A filter because I had found from previous experience that it brought out the Reds nicely leaving a greenish/orange tone that I found pretty different and refreshing for a redscale.

Some background on understanding a Redscale will help us predict the final look with filters:

Rescale has two filters built-in -

(1) An Orange/Magenta base and an anti-halation layer, which blocks more blue and green light than it does red.

(2) A yellow filter that blocks most of the blue light from the blue emulsion.

We need the yellow filter because

the green layer is actually quite sensitive to blue light,
and sometimes the red layer is a little as well (e.g. see the tech details for Kodak Portra, page 8 has the spectral sensitivity graph)

So in the normal arrangement

you get blue on top,
then the filter, so that the red and green emulsions are exposed to only the red and green light.

That extra sensitivity where it's usually not wanted is a big part of the redscale look. For something white, normally you'd get equal exposure for red, green and blue - With redscale, it works a little differently:

Orange base colour leaves more red light than blue and green.
Red emulsion gets exposed by lots of red light, some green light, and a tiny bit of exposure from blue.
Green emulsion gets lots of exposure from green light, and a fair amount from blue, but there's not as much green and blue light (thanks to orange base)
Most blue light is filtered by yellow filter.
Very little or no exposure of the blue emulsion takes place.

So white turns out with quite a bit of red and some green;

red + green = yellow

technically, it's subtractive color,

red emulsion -> cyan dye,
green emulsion -> magenta dye,
white light - cyan - magenta = yellow,

which you can see in the clouds in a lot of pictures below.

We can guess what stacking filters on top of this will do by remembering what sort of light each filter lets through.

Red is probably simple: it cuts out essentially all green and blue light, so you'd be exposing the red emulsion to only red light. At a guess, probably not that different from shooting normal film with a red filter.
Orange is probably similar, since it still cuts a lot of green, and all blue.
Yellow filters cut out the blue light, which contributes to exposure of the green emulsion, so likely cuts down on the amount of yellow in the final result, and would probably eliminate any of the residual blue you get with some films.
Blue filters let through only blue light, which mostly exposes the green emulsion, then is filtered out:

This might be interesting, as you'd get a lot more green than red in the final result, but it's going to need even more exposure over normal red scale, maybe 3-4 stops extra in total (i.e., ISO 400 shot as if it was ISO 50).