Astronomik Filters HSO 12nm 50mm (85952)

H-alpha Filter: This filter is ideal for photographing hydrogen nebulae from both light-polluted areas and dark sky locations. It greatly enhances the contrast between objects glowing in H-alpha light and the sky background.

With a narrow 12 nm half-width and nearly 100% transmission at the H-alpha wavelength, this filter offers significantly greater contrast than broadband filters. The 12 nm half-width is optimized for use with typical CCD and CMOS sensors.

In large cities, images taken with cooled CCD cameras are usually limited by dark current, not by the brightness of the sky. Therefore, using filters with an even narrower half-width does not reveal additional object details. 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 allows use on any instrument with an aperture ratio as fast as f/3. Note that Astronomik H-alpha filters are not suitable for solar observation.

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

OIII Filter: This narrowband filter is tuned to the OIII emission line at 500.1 nm and is suitable for both observation and imaging of OIII regions in either light-polluted or dark sky conditions. The OIII filter increases contrast between specific astronomical objects—such as supernova remnants and planetary nebulae—and the background sky. 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 completely 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, images taken with DSLRs and most cooled CCD cameras are limited by the camera’s dark current, not by sky brightness. In this case, using a filter with a smaller half-width will not show more object details. The 12 nm filters make it easier to find 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 highly light-polluted locations. These filters provide even greater sky suppression 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 best for heavily light-polluted areas, advanced cooled cameras, or when maximum contrast for faint objects is needed.

Specifications

• Half-value width: 12 nm

• Filter size: 50 mm

• Frame: Ring

• Mount material: Aluminium

• Optical coating: MRF

• Number of filters: 3

• Type: Line filter

• Series: HSO