Chroma H-beta Filter - 5nm

Isolating the 486.1 nm H-beta Line with a 5 nm Bandpass

The Hydrogen-beta emission line at 486.1 nm comes from nebulae rich in ionized hydrogen, and a narrowband filter is needed to separate it from nearby blue and green spectral lines (Chroma). This filter uses a 5 nm bandpass to isolate the H-beta signal, increasing contrast on targets like the California Nebula (NGC 1499), IC 434 behind the Horsehead Nebula (Barnard 33), and the Cocoon Nebula (IC 5146).

Stable Performance Down to f/2: A Measured 1.7 nm Shift

While officially designed for systems f/4.0 or slower, measured data shows this 5 nm filter holds its transmission well in faster telescopes. At f/4, the center wavelength shifts just 0.5 nm to 485.6 nm with 99.5% peak transmission. In an extremely fast f/2 system, the center wavelength moves only 1.7 nm to 484.4 nm, with 97.3% peak transmission. The 486.1 nm H-beta line stays inside the half-maximum band (481.7 to 487.0 nm at f/2), though close to its red edge.

Research-Grade Build: 3.0mm Substrates and Better Than 0.25 Wave/inch Wavefront

Chroma's astronomy filters are built in Vermont, USA, using durable sputtered hard coatings on a single 3.0 mm thick glass substrate with no laminations. The rear surface features an anti-reflection coating to prevent ghosting, while the transmitted wavefront of better than 0.25 waves/inch helps preserve the sharpness of your telescope's optics.

• Sputtered Hard Coatings: Built to withstand humidity changes and temperature swings and remain spectrally accurate in centre wavelength and bandpass (Chroma).
• Parfocal Design: At 3.0 mm thick, this filter is parfocal with other Chroma astronomy filters (except LoGlow), eliminating the need to refocus when switching between LRGB and other narrowband channels.
• Single Substrate: One substrate with no laminations; the rear anti-reflection coating prevents ghosting and maximizes transmission.

Sizing for Every System: From 1.25" Mounted to 50mm Square

Chroma offers the 5nm H-beta filter in six sizes. Mounted versions include standard 1.25" (M28.5x0.6 thread) and 2" (M48x0.75 thread) cells. For larger filter wheels, unmounted round filters are available in 31 mm, 36 mm, and 50 mm diameters, along with a 50 x 50 mm square option.

Chroma 5nm vs. 3nm H-beta: Throughput vs. Contrast

Choosing between a 5 nm and a 3 nm filter involves a direct trade-off between signal throughput and background rejection. The 5 nm H-beta filter is the more versatile and forgiving option, especially for imagers with a wide range of telescopes.

• 5nm Bandwidth (This Filter): Offers higher signal throughput and is significantly more tolerant of the blue shift that occurs in fast focal ratio systems (f/5 and faster). For beams faster than f/3, use 5 nm or wider bands.
• 3nm Bandwidth: Provides higher contrast by rejecting more background skyglow and starlight. However, it is far more sensitive to focal ratio-induced blue shift, which can push the emission line to the edge of the passband and reduce signal. It performs best in systems at f/5 or slower and under heavily light-polluted skies.