Because panchromatic black-and-white film is sensitive to all visible wavelengths, colored optical glass filters placed before the lens alter how colors render into gray values.
1. Classic B&W Contrast Filter Selection Matrix
| Filter Type | Wratten Number | Exposure Filter Factor | Visual Photographic Effect |
|---|---|---|---|
| Light Yellow | #8 (K2) | +1 Stop (2×) | Natural sky correction; clouds pop against soft gray skies |
| Medium Orange | #16 or #21 | +1.66 Stops (3×) | Darkens blue skies moderately; penetrates haze; softens skin blemishes |
| Deep Red | #25 (A) | +3 Stops (8×) | Dramatic almost-black skies; stark white clouds; wood effect foliage |
| Deep Green | #58 | +3 Stops (8×) | Lightens green plant leaves; enhances Caucasian lips; natural outdoor portraits |
| Infrared (IR) | #87 (R72) | +5 to +6 Stops (32×) | Total Wood Effect: luminous white foliage against pitch black sky |