Astronomik H-alpha 12nm CCD 27mm, unmounted (SKU: 10212327 / 8h00mh)

Astronomik H-alpha 12 nm 27 mm unmounted filter (Astronomik, SKU: 10212327) is a narrowband filter for imaging nebulae emitting light from hydrogen H-alpha at 656 nm. Its 12 nm full width at half maximum increases the contribution of the selected emission relative to the sky background, both at dark sites and under light pollution.

The filter suppresses light outside the useful passband, from UV to IR. It can be used for monochrome imaging or to build composites from exposures taken through several emission-line filters. Exposure time and channel balance depend on the brightness of the individual lines, camera sensitivity and sky conditions.

The 12 nm passband preserves more starlight than narrower versions, which can help when guiding uses light passing through the filter. It is a useful entry into narrowband imaging; a narrower passband does not always help when the exposure background is mainly limited by camera noise.

The 27 mm version is supplied unmounted and without a protective ring. Its 1 mm glass requires a suitable holder in a filter wheel or drawer. The holder must match the filter diameter and thickness without applying excessive pressure to the glass.

The H-alpha filter is not a solar filter and must not be used for observing or imaging the Sun.

Key features

• passband: H-alpha, 12 nm full width at half maximum
• suppression of unwanted out-of-band light from UV to IR
• recording of one emission-line channel for later combination
• coating: Astronomik MFR
• durable coatings resistant to scratching and moisture

Included items

• filter: Astronomik H-alpha 12 nm 27 mm unmounted filter
• protective filter box

Technical specifications

• manufacturer: Astronomik
• manufacturer product code: 10212327
• type: H-alpha narrowband emission-line filter
• full width at half maximum (FWHM): 12 nm
• guaranteed transmission: over 90% at the H-alpha line at 656 nm
• typical transmission: 96% at the H-alpha line at 656 nm
• out-of-band blocking: from UV to IR
• coating: Astronomik MFR
• recommended focal ratio range: f/3–f/∞
• diameter: 27 mm
• construction: unmounted, without protective ring
• mechanical thickness: 1 mm
• glass thickness: 1 mm
• material: finely polished optical glass
• optical quality: diffraction-limited
• coating resistance: to scratching, moisture and ageing
• parfocality: with standard Astronomik filters using 1 mm glass
• quality control: individual measurement of spectral response

Selective H-alpha imaging helps reveal nebular structure with a reduced sky-background contribution.

Product code: FILAST27-8H00MH_AIK