Astronomik Filters HSO 6nm 50mm (85957)

H-alpha Filter: This filter is designed for photographing hydrogen nebulae in both light-polluted environments and dark-sky locations. It greatly enhances the contrast between objects that emit H-alpha light and the surrounding sky background.

SII Filter: The SII filter is ideal for capturing sulfur emission regions, whether you are shooting from light-polluted areas or dark skies. It significantly increases the contrast between objects glowing in the sulfur line at 672 nm and the sky background.

By combining a narrow 6 nm half-width with nearly 100% transmission in the SII line, the filter provides maximum signal at the target wavelength while blocking all other unwanted light, ensuring an extremely dark background.

OIII Filter: The 6 nm OIII filter dramatically boosts contrast between galactic nebulae and the sky background. Its narrow half-width and high transmission in the OIII line maximize the desired signal while effectively blocking all other wavelengths, resulting in a very dark background for enhanced detail.

The 6 nm half-width is perfectly suited for CCD and CMOS sensors with especially low dark current. These filters are the top choice for locations with heavy light pollution or whenever faint objects must be captured in regions of the sky crowded with stars.

Choosing the Right Half-Width:
When shooting under dark skies, images from DSLRs and many cooled CCD cameras are limited by the camera’s dark current, not by sky brightness. In this case, narrowing the filter’s half-width further will not show more object detail. The 12 nm filters are generally easier for finding tracking stars, especially with cameras that have built-in tracking sensors.

For cameras with exceptionally low dark current and good cooling, 6 nm filters offer maximum benefits: stronger suppression of sky brightness, longer possible exposures, and deeper images. The very narrow bandpass makes stars appear tiny, and faint stars may vanish—an advantage in star-rich regions like the Milky Way, where faint nebulae can stand out in high contrast.

Summary:

• 12 nm filters are recommended for DSLRs and cameras with higher dark current.

• 6 nm filters are best for very light-polluted sites, cameras with extremely low dark current, or for capturing faint objects that require maximum contrast.

Specifications

• Half-value width: 6 nm

• Filter size: 50 mm

• Frame: Ring

• Mount material: Aluminium

• Optical coating: MRF

• Number of filters: 3

• Type: Line filter

• Series: HSO