Askar 6nm Colour Magic Super Ha/OIII D1 Filter - 2"

The Askar D1 filter is designed for astrophotographers using one-shot color (OSC) cameras in light-polluted areas. It allows you to capture two key nebula emission lines, H-alpha and OIII, in a single exposure, which dramatically increases image contrast and reveals details that would otherwise be lost to skyglow.

This is a deliberate design choice to balance signal strength with contrast. The tighter 6.5nm OIII bandpass provides excellent rejection of light pollution around that wavelength. The slightly wider 8.5nm H-alpha bandpass allows for slightly more signal collection, which can be beneficial for capturing fainter hydrogen structures in deep-sky objects.

It will perform exceptionally well. The Orion Nebula is extremely rich in both H-alpha and OIII emissions. The Askar D1 will isolate these signals, enhancing the red nebulosity and bringing out the blue-green structures in the core, all while suppressing skyglow. This allows for greater control over the bright Trapezium region while capturing the faint outer loops.

While you can, it's not the ideal application. A monochrome camera would capture both H-alpha and OIII signals on the same frame, preventing you from processing them separately. For monochrome imaging, using individual H-alpha and OIII filters provides far more flexibility and control over the final color image.

Yes. The filter's optical design has been tested to minimize band-shift and maintain high transmittance on systems as fast as f/1.9. This makes it a very capable choice for fast astrographs like the RASA, allowing you to take full advantage of the instrument's light-gathering power without significant signal degradation.

Halos are minimized through a combination of factors. The ≥OD5 blocking and anti-reflection coatings reduce stray light, while the 30" parallelism specification ensures that light passes through without creating internal reflections that can cause halos and other artifacts around bright stars.