Diffusion filters: used to scatter light and reduce image resolution – to soften hard edges.
Fog filters: used to scatter light from the bright part of the image to the dark part, creating a foggy effect over the picture.
Graduated filters/grads: filters with neutral density or color on one part of the glass, graduating to clear glass.
Low contrast filters: used to reduce the contrast of a scene – useful when shooting in exteriors with heavy contrast.
Matte: an opaque mask placed in front of the lens to black out a portion of the image. Whatever part is blocked is filled later with another image element – such as a mountainous vista - which is shot separately.
Net: a hair net used as a form of diffusion.
Neutral density filters: colorless filters in a range of densities, used to reduce the amount of light entering the lens when the intensity is too great for the film stock or the required f-stop. Can be used in the camera or over windows.
Pola screen: used to polarize light and eliminate reflections in glass, glare from a bright light source and flares (if used at certain angle). Is also used to deepen the color in a blue sky and make the clouds “pop” out.