Brightwell Nightline H-beta filter 2 in, observatory grade

Specifications

Description

The Nightline H-beta is a narrowband nebula filter in a 2 in threaded cell. Its passband is about 12 nm wide and centred near the hydrogen-beta line at 486 nm, with a peak transmission of about 85 percent. It blocks most of the rest of the visible spectrum, including the doubly ionized oxygen lines at 496 and 501 nm and much of the glow from artificial lighting.

Emission nebulae shine at the hydrogen-beta wavelength, while the sky background spreads its light across the spectrum. By passing the nebula's light and blocking most of the background, the filter raises the contrast between the two. The nebula does not become brighter, but the sky around it darkens, so faint outer filaments can become visible. Hydrogen-beta emission is weaker than hydrogen-alpha, so the gain is smaller than with a deep-red filter. You will notice the effect most under moderately dark skies with a telescope of 150 mm aperture or more. Good targets include the outer regions of the Orion Nebula, the Rosette Nebula, and the Veil Nebula.

A hydrogen-beta filter does not help with galaxies, star clusters, or reflection nebulae, which emit across a broad range of wavelengths. On those targets the filter mainly dims the view, and stars appear bluish. Planetary nebulae such as the Ring Nebula respond to it, but a broader UHC or OIII filter often suits them better. The filter screws into the barrel of any 2 in eyepiece, the nosepiece of a 2 in diagonal, or a 2 in filter cell. The glass is coated on one side with a multi-layer interference stack and on the other with an anti-reflection layer.

About this configuration

The Brightwell Nightline H-beta filter 2 in is offered in several configurations, and the notes below describe what this particular one includes. The observatory grade comes with a measured transmission curve for the individual filter in the box. Observatory grade glass has the tightest flatness tolerance in the Nightline line, which suits imaging with long focal lengths. Hard-sputtered layers keep their passband stable over time, which matters if you compare images taken years apart.

An aluminum case with a foam insert keeps the filter safe during travel to a dark site. The 2026 edition carries the glass over unchanged and updates small parts such as the case and the labels. The transmission figures in the specifications apply to every configuration of the Nightline line.

What's in the box

• H-beta filter in 2 in threaded cell
• Plastic storage case
• Test report with measured transmission curve
• Aluminum storage case

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter cells (M48 x 0.75).
• Works best in telescopes of 150 mm aperture and larger under moderately dark skies.