If you hold these filters up to the light, you can easily see a line where the colors meet. To keep this line from being obvious in your photo, align it with a natural separation line or dark area in the scene. Also avoid using a small aperture with a wide-angle lens, or the dividing line may show as a fuzzy line in your photo. Not all subjects will look attractive with all filter colors. Experiment with different colors before you shoot.
Graduated filters have a colored area that gradually changes in density and a clear area.
Position the clear area over the part of the scene that you want to reproduce realistically, and use the colored part to add color to the rest of the scene. For example, you could use a blue graduated filter to add color to an unattractive gray sky. With graduated filters, as with dual-color filters, you can vary the position of the colored areas by rotating the filters and experimenting until you get the effect you want. Star filters turn point sources of light and specular highlights into stars. The stars are created by cross-hatched lines engraved on the surface of the filter.