Astronomik Filters HSO 6nm 2" (85954)

H-alpha Filter: This filter is ideal for photographing hydrogen nebulae, whether you are working in light-polluted areas or under dark skies. It significantly enhances the contrast between objects that emit H-alpha light and the background sky.

SII Filter: The SII filter is suitable for imaging sulfur emission regions from both light-polluted locations and dark-sky sites. It greatly 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 maximizes the signal at the desired wavelength while blocking unwanted light, ensuring an extremely dark sky background.

OIII Filter: The 6 nm OIII filter is designed to dramatically increase the contrast between galactic nebulae and the sky background. With its narrow half-width and high transmission in the OIII line, it delivers maximum signal at the target wavelength and effectively blocks all other radiation, resulting in a very dark sky background.

The 6 nm half-width is specially optimized for CCD and CMOS sensors with very low dark current. These filters are the preferred choice for locations with heavy light pollution or whenever faint objects need to be captured in areas of the sky with many 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 rather than the sky brightness. In these cases, a narrower half-width does not reveal more object detail. The 12 nm filters are generally easier to use for finding tracking stars, especially with cameras that have built-in tracking sensors.

For cameras with extremely low dark current and strong cooling, 6 nm filters offer all their advantages: they provide even stronger suppression of sky brightness, allowing for longer exposures and deeper images. The narrow half-width means stars become tiny and faint stars may disappear, but faint objects remain high in contrast—even in star-rich regions like the Milky Way.

Summary:

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

• 6 nm filters are best for highly light-polluted locations, for cameras with very low dark current, or when faint objects need maximum contrast.

Specifications

• Half-value width: 6 nm

• Frame: 2"

• Mount material: Aluminium

• Optical coating: Multiple coatings

• Connection to telescope: 2"

• Number of filters: 3

• Type: Line filter

• Series: HSO