Brightwell Nightline H-beta filter 2 in, premium 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

This listing covers one configuration of the Brightwell Nightline H-beta filter 2 in, defined by its grade, coating, case, and edition year. The premium grade uses polished glass with tighter flatness tolerances, which helps at high magnification. Premium grade filters are checked for the position of the passband before they leave the factory. Hard-sputtered layers keep their passband stable over time, which matters if you compare images taken years apart.

A padded pouch is easy to open with cold fingers, which helps when you swap filters during a session. The 2023 edition uses the same coating design as later years, with small differences in the cell markings. 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
• Padded pouch

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.