The diagram below shows the typical bandpass of these 3 types.  This diagram presents a simplified representation of the filter bandpasses; see the diagrams from the various vendors for specifics on their filter response.  The x axis is the wavelength of light across the visual range from violet (400 nm) to deep red (700 nm).  The y axis is the percentage of the light that the filter passes at that wavelength.  The Oxygen-III and Hydrogen –Beta & - Alpha labels mark the emission lines of oxygen and hydrogen.

Broadband filters, which are also called light pollution filters, are not considered to be nebula filters.  They have a much wider passband designed to aid with deep-sky observing in moderately light-polluted skies by blocking the most common wavelengths of light pollution - that produced by low pressure sodium and mercury vapor outdoor lamps - while providing for transmission of the rest of the visual spectrum.  Broadband filters can help with deep sky observing to some extent but don’t expect them to magically make the sky dark through the eyepiece of a scope.  The first key point to remember about filters is that they do not make objects brighter, only dimmer!  What they can do is improve contrast making an object easier to see and will often bring out more detail.

 The second two types in the diagram are what are considered to be nebula filters: Narrowband and Line.  Narrowband filters pass light in a region that encompasses both hydrogen-beta and oxygen-III lines.  Some narrowband filters such as the Lumicon UHC and the Thousand Oaks have a hydrogen alpha bandpass while the Orion Ultrablock does not.  Line filters are very narrow filters which pass a specific emission line or set of lines.  The O-III filter is by far the most widely used line filter.

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