Askar 3nm Colour Magic Ultra Ha/OIII E1 Filter - 2"

Dual-Bandpass Imaging with 85% Peak Transmittance

Designed for one-shot color cameras, the Ultra E1 captures the two most important emission lines simultaneously, drastically reducing total imaging time. By passing light at both 656.6nm (Ha) and 500.7nm (OIII) with 85% efficiency, you gather data for both the red and blue-green structures of targets like the Veil Nebula or the Rosette Nebula (NGC 2237) in a single set of exposures. This dual-band approach streamlines your workflow without compromising signal strength.

3.7nm & 4.0nm Bandwidths for Extreme Light Pollution Rejection

The defining feature of this filter is its extremely narrow full-width at half-maximum (FWHM). The 3.7nm band for Ha and 4.0nm for OIII aggressively reject unwanted light, including severe urban light pollution and natural skyglow. This surgical isolation of the nebula's signal creates a jet-black sky background, making faint, wispy details pop with dramatic contrast even from city backyards.

OD5 Blocking and 30" Parallelism for Halo-Free Stars

Optical precision extends beyond the passbands. The filter provides ≥OD5 blocking across the wide 200-1100nm spectrum, ensuring that stray UV and IR light, which can cause halos on bright stars, never reaches the sensor. A parallelism of 30 arcseconds guarantees the filter will not introduce distortions or degrade the sharpness of your optical system, maintaining pinpoint stars across the field of view.

Askar 3nm Ultra vs. Wider Dual-Band Filters: Contrast and Star Size

Compared to filters with 7nm or wider bandpasses, the Askar 3nm Ultra E1 offers a significant advantage in signal-to-noise ratio under light-polluted skies. The trade-off for this extreme contrast is a slight reduction in star brightness and potentially longer sub-exposure times to achieve the same signal level.

• Askar 3nm Ultra E1: Delivers maximum nebula contrast by eliminating more background light. It is the superior choice for imaging from Bortle 7-9 locations or during bright moon phases.
• Wider Dual-Band Filters: Capture signal faster and often produce smaller, more natural-looking stars, as very narrow filters can sometimes slightly bloat the brightest stars due to diffraction effects. They are excellent for dark sky sites where light pollution is less of a concern.