Essential for slides, warmers counteract the blue cast of light under trees or overcast skies; they also give a healthy glow to portraits. Their designation is usually taken from Kodak's Wratten filters, numbered, in increasing strength, 81A, 81B, 81C, etc. In b&w at the maximum (81EF), they add dramatic contrast between clouds and sky. We used the B+W KR-3 [81C] warming filter ($70, street). For info: www.schneideroptics.com; 800-228-1254.