Band pass filter can separate a band of monochromatic light, the ideal transmittance of band-pass filter through the bandwidth is 100%, while the actual band-pass filter pass band is not the ideal square. The actual band-pass filter generally has a center wavelength λ0, a transmittance T0, a half width of the pass band (FWHM, a distance between two positions where the transmittance in the pass band is half the peak transmittance), the cutoff range and other key parameters to describe.

Bandpass filter is divided into narrow-band filter and broadband filter.

In general, a very narrow bandwidth or high cut-off steepness will make the product more difficult to process; meanwhile the pass band transmittance and cut-off depth is also a contradictory indicator

Hyperion Optics' band-pass filters are composed of a stack of equally spaced dielectric layers. The number of layers and thicknesses are calculated with excellent cut-off depth (typically up to OD5 or higher), better steepness and a high transmittance (70% narrowband, 90% broadband).