The Celestron H-alpha, H-beta & OIII imaging filter for the RASA 8" allows high transmission of light from emission nebulae while blocking light pollution, helping to make your images pop with detail off the black sky background with superior contrast.

Fortunately, many sources of light pollution have relatively discreet emission spectra; they emit primarily at specific wavelengths of light. By strategically blocking these “bad” wavelengths, the filter essentially eliminates the effect of light pollution while letting the “good” wavelengths of light associated with the emission nebula pass through to the camera.

You’ll notice much higher contrast in your images immediately, even if imaging from your light polluted backyard! And since the transmission at the key wavelengths is so high, the nebula will not be dimmed—only the background will be blacker.

The transmission spectrum for the Ha-Hb-OIII Imaging Filter is 85% or greater at key wavelengths (486nm, 496nm/501nm, 656nm) and less than 0.5% transmission elsewhere. Because of this, it will not work well on broadband emission objects, such as galaxies and star clusters.

Other similar imaging filters on the market have much narrower bandpasses at the critical Ha-Hb-OIII wavelengths, but these filters will actually block much of the incoming Ha-Hb-OIII light for an F/2 optical system. This is because the light is coming into the filter at a steeper angle, which causes a spectral shift. Using filters not designed specifically for use at F/2 will cause some of the light from the nebula to be blocked, resulting in a dimmer image.

The Celestron Ha-Hb-OIII Imaging Filter for the RASA 8 was custom engineered to work at F/2, so none of the “good” light from the nebula is inadvertently blocked by the filter.

The filter fits directly into the internal filter mount in the RASA 8’s front lens cell, where the optical window normally mounts. By removing the clear window and replacing it with the filter, optical performance for the entire system is maintained.

Each filter comes with a plastic storage case to safely store the filter or the placeholder glass that came with your RASA when not in use. You will also receive a spectral transmission graph unique to your specific unit, verifying its performance.

Specifications