Editing Filters (section)

=== Broadband vs Narrowband ===
----When imaging with a mono camera, there are two main methods by which to obtain color.  One method is through “broadband” imaging (also called RGB imaging), and the other is through “narrowband” imaging.  In a broadband image, color is collected through filters that are provided by the astrophotographer, and mimick the Bayer array.  The color filters used are red, green, and blue.  Broadband imaging provides a significant increase in resolution of a given sensor, because during an exposure the entire chip is being utilized to collect the light.  In a OSC camera, only the pixels under a given color are being used, which, depending on color, is 25% or 50% of the total number of pixels.  So, by broadband imaging with a red, green, and blue filter, you are increasing the effective resolution of your image by 25%, 50%, and 25%, respectively, as compared to a OSC camera with the same sensor.  Of course, using this method, the filters need to be purchased and maintained separately from the camera, more for the astrophotographer.

Narrowband imaging is an entirely different technique.  Whereas broadband imaging says “I'm going to collect ALL wavelengths of light between 600-700nm and call that red” in order to get color, narrowband imaging says “I'm going to pick ONE wavelength, say 656.3nm, and call that red.”  Therefore, when narrowband imaging, the astrophotographer is essentially picked one wavelength of light he/she would like to record, and providing a filter that does exactly that.  The most common wavelength of light that is imaged in this method is hydrogen alpha (Ha) which gives off light of 656.3nm.  There are many astronomical objects that give off this light, and so there are many “Ha” targets available for a narrowband imager.  Unfortunately, since this light is limited to a single wavelength, often very long exposures are needed in order to collect enough light such that the signal to noise ratio is high enough to generate a good image.  This is why an expensive, high quality, mono-CCD is used with narrowband imaging.  Other common narrowband wavelengths are shown in figure 2, such as oxygen three (OIII) at 495.nm, and 500.7nm.  Do note there is some 'width' to which what wavelengths a narrowband filter lets through. I.e. 7nm, 3nm.