Brightwell Nightline H-beta filter 2 in

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 standard grade uses the same coating design as the higher grades, with wider tolerances on flatness. Standard grade glass suits visual observing at low and medium magnification. A standard coating suits visual use, where small reflections between filter and eyepiece rarely show.

A padded pouch is easy to open with cold fingers, which helps when you swap filters during a session. This is the 2024 edition, which revised the cell knurling and the case insert of the Nightline line. Check the size in the specifications against your eyepiece barrels, star diagonal, or filter wheel before you choose.

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.