Efke 25 red sensitivity & exposure correction

Take a look at this spectral sensitivity graph:

http://www.jandcphoto.com/index.asp?PageAction=Custom&ID=1

Notice that KB 50 is almost the same but KB 100 goes almost to 700nm.

I've shot this film with a yellow filter but want to go with a red filter. If I do that it looks like I'll have some trouble with underexposure. Should I just use another film with the red filter or has somebody done this and has a correction factor to use? I'm shooting 35mm so am attracted to very slow fine grain films.

Thanks,

Doug

The Efke is orthochromatic as far as I know, meaning it wouldn't work well with a red filter (you're filtering out all of the usable wavelengths).

For slow, fine grained films, I'd probably use the Ilford PanF+ for these instances. I used to use Agfa APX25 (rest in peace), and liked Efke KB-25 except for the filter problems. Then I used the PanF for a while. Now I don't mind the grain so much anymore.

- Thom