Astronomik H-alpha 12nm XT Clip-Filter

The Astronomik H-alpha 12nm XT Clip-Filter is a premium narrowband emission-line filter engineered for imaging hydrogen nebulae from both light-polluted and dark observation sites. It isolates the H-alpha emission line at 656nm, dramatically enhancing contrast between hydrogen-alpha-emitting objects and the sky background — while blocking sodium (Na) and mercury (Hg) vapour lamp emissions, LED light maxima, natural airglow, and moonlight from UV through IR.

The XT (Extra Thin) version is coated on an ultra-thin 0.3–0.5mm substrate, specifically designed for wide-angle lens astrophotography. This significantly reduces optical aberrations that standard clip-filters can introduce at the edges of widefield images, delivering sharp, crisp stars all the way to the corners.

⚠ WARNING: This filter MUST NOT be used for solar observation.

Why 12nm FWHM?

The 12nm Full-Width-Half-Maximum bandpass is the ideal choice for DSLR and mirrorless cameras with CMOS sensors, CCD cameras with normal-to-high dark current, and imaging from suburban or dark-sky locations. It also passes more guide stars than narrower alternatives (6nm / 4nm), making it the preferred option for cameras with integrated or dual guiding sensors. In low light-pollution areas, the background signal is typically limited by sensor dark current rather than skyglow — so a narrower FWHM provides no additional benefit.

Choose Your Coating: MFR or MaxFR

Both coatings deliver exceptional out-of-band blocking from UV to IR, extremely high contrast, minimised stray light, zero halos, and needle-sharp stars.

MaxFR variants are available for Canon EOS R, Nikon Z, Nikon XL, and Sony Alpha 7 mounts.

Choose Your Camera Mount

Select the clip-filter variant that matches your camera body. Each clips directly into the camera's lens mount — no tools, no camera modifications, no adapters required. All lens functions (focus, aperture, image stabilisation) remain fully operational.

* Nikon D780 & D850: after a firmware update, electronic-contact lenses require a workaround (tape over lens contacts) or use of manual-focus lenses / T-adapters only.

Advantages of the Clip-Filter Design

• Installs and removes in seconds — no tools or camera modifications needed, even in the dark
• All lens functions (focus, aperture, IS) remain fully operational
• Works with both camera lenses and telescopes
• Eliminates the cost of oversized front-mounted filters for large lenses
• No back-focus shift — unlike filter drawers or holders between body and lens
• Compatible with fast astrographs (e.g. Vixen R200SS, Takahashi Epsilon) where filter wheels can't be used
• Doubles as a sensor dust shield during long exposures

XT (Extra Thin) Technology

Standard clip-filters can introduce star elongation in the outermost corners when used with very short focal length lenses. The XT series solves this with an ultra-thin 0.3–0.5mm substrate — significantly reducing aberrations while maintaining the highest optical quality: finely polished, striae-free, stress-free, bubble-free glass suitable for the most demanding imaging applications.

XT filters use the same durable coating technology as all Astronomik filters — extremely scratch-resistant, humidity-proof, and backed by a 10-year warranty.

Technical Specifications

Known Incompatibilities

• Canon EOS R mount: Not compatible with RF 35mm F1.8 IS Macro STM, RF 85mm F1.2L USM, Extender RF 1.4x, Extender RF 2x
• Canon EOS APS-C: Not compatible with Canon EF-S series lenses (third-party, M42, and T2 adapters are fine)
• Nikon Z: Not compatible with Nikon Z TC-2.0x teleconverter
• Canon EOS Ra: Compatible but not recommended — the Ra shows strong halos around bright stars even without a filter
• Canon EOS 5D Mark IV, 5DS, 5DS R, 6D Mark II: Not compatible with EOS XL clip-filter

What's in the Box

• 1× Astronomik H-alpha 12nm XT Clip-Filter (in selected mount variant and coating)
• High-quality protective filter box
• Individual spectral measurement data label