Astronomik Filters HSO 12nm 36mm (85951)

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

With its narrow 12 nm half-width and nearly 100% transmission at the H-alpha wavelength, this filter achieves significantly higher contrast than broadband filters. The 12 nm half-width is perfectly suited for typical CCD and CMOS sensors.

In most urban environments, images taken with cooled CCD cameras are usually limited by dark current rather than background sky brightness. As a result, using filters with an even narrower half-width does not necessarily reveal more detail. The H-alpha 12 nm filter also makes it easier to find tracking stars, which is useful for cameras with built-in tracking sensors. The advanced MFR coating technology allows use on any instrument with an aperture ratio as fast as f/3. Astronomik H-alpha filters are not suitable for solar observation.

SII Filter: The SII filter is designed to boost contrast between sulfur emission regions and the sky background. With its 12 nm half-width and high transmission near 100% in the SII line, it delivers much greater contrast than broadband filters. Like the H-alpha filter, it is optimized for CCD and CMOS sensors and helps in locating guide stars with cameras that have tracking sensors.

OIII Filter: This narrowband filter is tuned to the OIII emission line at 500.1 nm and is suitable for observing and photographing OIII regions in both light-polluted and dark sky conditions. The OIII filter enhances contrast between specific astronomical objects—mainly supernova remnants and planetary nebulae—and the sky background. Thanks to its narrow half-width and high transmission, it outperforms wider-band filters. It is effective for telescopes from 150 mm aperture at medium magnification, as well as for astrophotography with any lens or telescope diameter.

The filter blocks emission lines from mercury and sodium lamps, as well as airglow, allowing only the two OIII lines to pass through with very high transmission.

Choosing the Right Half-Width:
When shooting under dark skies, both DSLR and many cooled CCD cameras are limited by their own dark current, not by the sky brightness. In this case, narrower filters will not show more details. The 12 nm filters are easier for finding tracking stars, which is especially helpful for cameras with built-in tracking sensors. The 6 nm filters are best for cameras with very low dark current and strong cooling, or for imaging faint objects in light-polluted locations. These offer even more suppression of sky brightness and higher contrast, though faint stars may disappear, and tracking stars can be harder to find.

Summary:

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

• 6 nm filters are ideal for heavily light-polluted locations, advanced cooled cameras, or when maximum contrast for faint objects is needed.

Specifications

• Half-value width: 12 nm

• Filter size: 36 mm

• Frame: Ring

• Mount material: Aluminium

• Optical coating: MRF

• Number of filters: 3

• Type: Line filter

• Series: HSO