Dichroic filters are far more accurate and efficient in their ability to block unwanted wavelengths when compared to gel and glass absorption filters. Short and long wavelength pass dichroic filters act as the names imply and allow transmission of only narrow bands of short or long wavelengths, reflecting the unwanted wavelengths. Bandpass dichroic filters are the most common and are designed to transmit selected wavelengths in the visible region. In this graph we have plotted the wavelengths that are transmitted by the filter versus the percentage of transmission. This filter is much more effective than the glass or lacquered gel magenta filter discussed above because there is virtually no passage of unwanted wavelengths and secondary transmission is almost nonexistent.
Notch filters are effectively the opposite of bandpass dichroic filters.
To use the example illustrated in the plot, a notch filter would pass the red and blue color wavelengths that are blocked with the bandpass filter. Dichroic filters are commonly used for a number of applications including specialized filtration for optical microscopy and photography. This allows the photographer a high degree of color correction control over photographic prints. Color Correction - Photographers and microscopists often must make slight corrections in the color of the illumination in photographic enlargers and microscope optical paths to insure accurate color rendition. Although we refer to the Kodak filters here, there are a wide variety of manufacturers that produce these filters made with dyed gels or dichroic glass.