Editing Filters (section)

=== UV-IR cut filters ===
----A UV-IR filter is a filter designed to limit the amount of light that makes it to the sensor to a certain predefined area of the visible and infrared spectrum.  Recall figure 1.  There is still plenty of light that has a wavelength less than 400nm (we call this ultra-violet), or greater than 700nm (we call this infrared, sometimes referred to as “deep infrared” or “deep IR”).  Since the astrophotographer likely does not want this light to hit his/her sensor (for various reasons that are beyond the scope of this entry), it needs to be filtered out.  That filtering is done by the UV-IR cut filter.  This filter is a single filter that, just like a light pollution filter, will not allow light with a wavelength less than 400nm, or greater than 700nm to pass.  Therefore, all light that DOES pass through this filter must be in an appropriate wavelength range, which is what the astrophotographer desires.  There are many UV-IR cut filters available, many of which will “cut out” light at different values.  For example, some will allow light of 699nm to pass, but 700nm is not allowed, while other filters will allow 700nm to pass, but 715nm is not allowed.  The varying values of the “cut off” point is a user selectable option.

Of course, there is no reason the UV-IR cut filter must be one piece of glass.  It is completely possible to only use an IR cut filter which will “cut out” all IR light (i.e. light with a wavelength greater than 700nm), but let all light less than 700nm pass.  The same can be said for the UV side of the spectrum.