I have been testing this 2-inch Celestron OIII (oxygen III) narrowband filter, which according to the specifications, isolates 496 nm and 501 nm lines emitted by planetary and emission nebula.
The filter looks like a polished mirror that allows some green light that corresponds to the light emitted by emission and planetary nebula to pass through but blocks everything else including most light pollution. It results in enhanced contrast between the sky and the nebula.
I have used this filter extensively in visual observation by “blinking” it in and out between the eye and the eyepiece, a technique used in observing emission and planetary nebula. I wanted to know if I could also use this filter to photograph OIII targets with an unmodified DSLR and a telescope and the results look good.
I am only beginning to discover narrowband imaging and I hope to use this OIII filter to photograph targets even in severely light-polluted sky.
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Night Sky in Focus | Astronomy and Amateur Radio © Anthony Urbano | Manila, Philippines