OK, if you look at the technical data for EFKE R25 film at: http://www.jandcphotography.com/efkedata.htm My question is, what effect will a #25 red filter have with this film? A red filter will pass it's own wavelength, which this film is not very sensitive to and it will block the lower blue wavelengths. If you look at the spectral sensitivity chart for this film, this leaves just about the green wavelengths with some red and whatever blue isn't filtered out. How would this look in landscapes in the sierras, for instance on a sunny day? Black skies, light evergreen trees, lots of contrast? Apparently only light within 500 - 600 nm will be hitting the film. Would a #12 yellow filter be a better choice so as not to give pitch black skies? What about close-ups of rocks and trees? I have read that shadows consists mostly of blue light, so a red filter would make the shadows thinner in the negative - no matter what the exposure, correct? After all if the red filter is removing the blue wavelengths, it doesn't matter how long one leaves the shutter open, the light from the shadows will not hit the film. EFKE PL 100 is much more red-sensitive so light from 500 - almost 700nm will be hitting the film with a Red #25 filter on so more light will be striking the film overall - green and well into the red. Is this correct or do I have this all wrong? I am going out tomorrow photographing in the sierras concentrating on granite rock and I was wondering what EFKE 25 with a #25 red filter would produce if the full frame is just a well illuminated piece of granite rock. Will it enhance texture strongly or will the negative be too contrasty? Thanks.