Celestron OIII Narrowband Filter

The 2-inch Celestron OIII (oxygen III) band-pass filter that allows the 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.

Celestron 93624 OIII filter

I used this filter extensively in visual observation by ‘blinking’ it in and out between the eye and the eyepiece, a technique used in observing O-III planetary nebula. The use of the filter results in enhanced contrast between the sky and the nebula.

Night Sky in Focus 
© Anthony Urbano | Bacoor, Philippines

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