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H- Alpha & Calcium K Filters

H- Alpha & Calcium K Filters

If you're interested in viewing solar prominences, solar flares, solar corona, and other unusual details using your exisiting telescope, then a Solar Hydrogen-Alpha (H-alpha) Filter is a perfect choice.  These high quality filters are designed for blocking all light except for the h-alpha wave length.  This is an important emission line for solar observation, as the Sun's surface layer contains a high proportion of hydrogen.  The H-alpha filter allows safe observation of the entire solar disc, providing superb views of prominences, chromosphere, and surface details such as sunspots, plagues, flares, filaments, and granulation.  They are meant for both visual observing and astrophotography.

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An H-Alpha filter for solar viewing is not to be confused with a hydrogen-alpha filter meant for astronomy.  A solar Ha filter is designed for a specific bandpass and is created with multiple layers of vacuum deposited coatings.  It also corresponds with the aperture of the equipment being used.  H-Alpha filters are traditionally designed for a refractor telescope and work in conjunction with a blocking (or energy rejection) filter that is also based upon the focal length of the telescope.  The general rule of thumb is to first add 100 to the blocking filter aperture and then keep your telescope's focal length within that limit.  For example, a 6mm blocking filter would be best for telescopes with 600mm or shorter focal length.

Because the Sun is dynamic, fast-moving events will often place the bandpass of light just above or below a specific “setting”.  For that reason, a solar h-alpha filter comes with a device, or “tuner”, that allows the filter to be shifted slightly to capture the event.  This is also the purpose of an etalon.  With H-alpha solar viewing, the narrower the bandpass of the filter, the greater the details can be observed.  To achieve this, filters can be “stacked”, which means placing two filters on top of each other to further fine-tune your view.  Double stacking is particularly popular for photography.  

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