Astronomik Filters HSO 12nm 31mm (85950)

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

Thanks to its narrow 12 nm half-width and almost 100% transmission at the H-alpha line, this filter provides much greater contrast than broadband filters. The 12 nm half-width is specifically optimized for use with typical CCD and CMOS sensors.

Even in large cities, images taken with cooled CCD cameras are usually limited by dark current rather than sky brightness. Therefore, making the filter even narrower does not necessarily reveal more detail in the object. The H-alpha 12 nm filter also makes it easier to find tracking stars for most cameras with built-in tracking sensors. The advanced MFR coating technology enables the filter to be used on instruments with aperture ratios 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 contrast between sulfur emission regions and the sky background. With its 12 nm half-width and nearly 100% transmission in the SII line, it offers significantly greater contrast than broadband filters. Like the H-alpha filter, it is optimized for CCD and CMOS sensors and helps in finding suitable guide stars for cameras with built-in tracking sensors.

OIII Filter: This narrowband filter is tuned to the OIII line at 500.1 nm, making it ideal for observing and imaging OIII regions in both light-polluted and dark sky locations. The OIII filter increases contrast between certain astronomical objects—such as supernova remnants and planetary nebulae—and the background sky. Its narrow half-width and high transmission outperform wider-band filters. The filter blocks emission lines from mercury and sodium lamps as well as airglow, while allowing both OIII lines to pass with very high transmission. It can be used with telescopes from 150 mm aperture at medium magnification, and with any lens or telescope diameter for astrophotography.

Choosing the Right Half-Width:
When imaging under dark skies, both DSLR and many cooled CCD cameras are limited by the camera’s dark current, not by sky brightness, so using a narrower filter does not necessarily add detail. The 12 nm filters make it easier to find tracking stars, especially for cameras with built-in tracking sensors.
For cameras with very low dark current and strong cooling, or for imaging faint objects in light-polluted locations, the 6 nm filters offer even stronger sky suppression and higher contrast, though it can make tracking stars harder to find.

Summary:

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

• 6 nm filters are best for highly light-polluted sites, cameras with extremely low dark current, and for achieving maximum contrast with faint objects.

Specifications

• Half-value width: 12 nm

• Filter size: 31 mm

• Frame: Ring

• Mount material: Aluminium

• Optical coating: MRF

• Number of pieces: 3

• Type: Line filter

• Series: HSO