Astronomik Filters HSO 6nm 36mm (85956)

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 designed for capturing sulfur emission regions, suitable for both light-polluted locations and dark-sky sites. It dramatically 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 provides maximum signal at the desired wavelength while blocking all other light, ensuring an extremely dark background.

OIII Filter: The 6 nm OIII filter greatly increases the contrast between galactic nebulae and the sky background. Its narrow half-width and high transmission in the OIII line allow the filter to deliver maximum signal at the target wavelength while blocking unwanted radiation, resulting in a very dark background and enhanced details.

The 6 nm half-width is perfectly suited for CCD and CMOS sensors with particularly low dark current. These filters are especially recommended for use in areas with strong light pollution or whenever faint objects must be recorded in regions of the sky with many stars.

Choosing the Right Half-Width:
When imaging under dark skies, both DSLRs and many cooled CCD cameras are limited by the camera’s dark current rather than sky brightness. In such cases, further narrowing the filter does not reveal more details in the object. The 12 nm filters are generally easier for finding tracking stars, especially for cameras with built-in tracking sensors.

If your camera has very low dark current and good cooling, the 6 nm filters provide maximum benefits: they offer stronger sky suppression, allow for longer exposures, and produce deeper images. The narrow half-width makes stars smaller and may cause faint stars to disappear, which is especially useful in star-rich regions like the Milky Way—faint objects remain visible with high contrast without being lost among the stars.

Summary:

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

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

Specifications

• Half-value width: 6 nm

• Filter size: 36 mm

• Frame: Ring

• Mount material: Aluminium

• Optical coating: MRF

• Number of filters: 3

• Type: Line filter

• Series: HSO