Brightwell Nightline H-beta filter 1.25 in, premium grade

Specifications

Description

The Nightline H-beta is a narrowband nebula filter in a 1.25 in threaded cell. It passes a band about 12 nm wide centered on the hydrogen-beta emission line at 486 nm and blocks most other visible light. Peak transmission is about 85 percent at the center of the passband, so the view is noticeably dimmer than an unfiltered view.

Emission nebulae shine most strongly at specific wavelengths, while the sky background and artificial lighting spread light across the visible spectrum. A narrow passband centered on the hydrogen-beta line blocks much of that background and passes the nebula's light, which increases the contrast between the two. The nebula itself does not become brighter. The sky around it becomes darker, so faint hydrogen-emitting regions near brighter structures become easier to see. The effect is greatest under moderately dark skies, where background glow is weaker.

Hydrogen-beta emission is strong in regions such as the Flame Nebula and the Horsehead Nebula in Orion, where you can view the glowing gas near Alnitak. Many emission regions in the Milky Way, including parts of the Cygnus region, also respond well. The filter passes little of the oxygen-III light at 496 and 501 nm, so you should not expect much from the Veil Nebula or from planetary nebulae that rely on oxygen emission. Galaxies, star clusters, and reflection nebulae shine in a broad range of colors, so on those targets the filter mainly dims the view.

The filter screws into the barrel of any 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal. The glass has a multi-layer interference coating on one side and an anti-reflection layer on the other. Handle the filter by its cell, and store it in its case when not in use.

About this configuration

The Brightwell Nightline H-beta filter 1.25 in is offered in several configurations, and the notes below describe what this particular one includes. 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. Anti-reflection coatings on both faces reduce halos around bright stars in the field.

A plastic case is light and stacks with other filter cases in an accessory box. The 2026 edition carries the glass over unchanged and updates small parts such as the case and the labels. A filter does not make objects brighter; it darkens the sky background more than the target, which raises contrast.

What's in the box

• H-beta filter in 1.25 in threaded cell
• Plastic storage case
• Plastic storage case

Compatibility notes

• Threads into 1.25 in eyepieces, diagonals, and filter wheels (M28.5 x 0.6).
• Most useful for emission regions that glow in hydrogen-beta light, under moderately dark skies.