Astronomik Filters HSO 6nm 1.25" (85953)

H-alpha Filter: This filter is designed for photographing hydrogen nebulae from both light-polluted areas and dark sky locations. It greatly increases 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, whether you are in areas with strong light pollution or under dark skies. It enhances 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, this filter delivers maximum signal at the desired wavelength while blocking all other light, resulting in an extremely dark sky background.

OIII Filter: The 6 nm OIII filter is ideal for maximizing contrast between galactic nebulae and the sky background. Its narrow half-width and high transmission in the OIII line ensure that only the target signal is passed, while unwanted light is blocked, creating a very dark background for enhanced detail.

The 6 nm half-width is specially optimized for CCD and CMOS sensors with very low dark current. These filters are the best choice for locations with extreme light pollution, or whenever faint objects need to be captured in star-rich regions of the sky.

Choosing the Right Half-Width:
When photographing under dark skies, images from DSLRs or many cooled CCD cameras are usually limited by the camera's dark current rather than the sky background. In these situations, narrower filters do not provide 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.

If you use a camera with exceptionally low dark current and good cooling, 6 nm filters offer all their benefits: they suppress sky brightness even more, allowing for longer exposures and deeper images. With the narrower half-width, stars appear smaller and fainter stars may disappear, but this is ideal for Milky Way regions with many stars, as faint nebulae can be shown in high contrast without getting lost among the stars.

Summary:

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

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

Specifications

• Half-value width: 6 nm

• Frame: 1.25"

• Mount material: Aluminium

• Optical coating: MRF

• Connection to telescope: 1.25"

• Number of filters: 3

• Type: Line filter

• Series: HSO