Brightwell Nightline UHC nebula filter 31 mm

Specifications

Description

The Nightline UHC nebula filter 31 mm is an ultra-high contrast nebula filter supplied as an unmounted 31 mm glass disc, for use in a holder or cell sized for 31 mm glass. It passes a band about 25 nm wide that covers the doubly ionized oxygen lines at 496 and 501 nm and the hydrogen-beta line at 486 nm, and it passes the hydrogen-alpha line in the deep red. Most other visible light is blocked, including much of the glow from artificial lighting.

Emission nebulae shine at those specific wavelengths, while the sky background glows across the spectrum. By blocking the background and passing the nebula's light, a UHC filter raises the contrast between the two. The nebula does not get brighter, but the sky around it gets darker, so you may see faint outer regions that were lost in the glow of the sky. Good targets include the Orion Nebula, the Lagoon and Trifid nebulae, the Swan Nebula, and planetary nebulae such as the Ring and the Dumbbell.

A UHC filter does not help with galaxies, star clusters, or reflection nebulae, which shine in a broad range of colors. On those targets it simply dims the view. Stars appear greenish through it, since the passband sits in the blue-green part of the spectrum. Because the glass is unmounted, handle it by its edges, keep the coated face clean, and store it in its sleeve when not in use. The effect is strongest in telescopes of 100 mm aperture or more and under moderately dark skies.

Set the filter in its holder with the coated side facing the eyepiece, as marked on the glass edge, and confirm that it sits flat without pinching. Compare the view with and without the filter at the same magnification to judge its effect on your target, since the change is most apparent on faint extended nebulae. Filters of this type work well at low to moderate magnification, where the nebula fills a larger part of the field.

About this configuration

The Brightwell Nightline UHC nebula filter 31 mm 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. Hard-sputtered layers keep their passband stable over time, which matters if you compare images taken years apart.

The padded pouch protects the filter from knocks and fits in a jacket pocket at the telescope. The 2025 edition keeps the same transmission figures as the earlier years of the Nightline line. The transmission figures in the specifications apply to every configuration of the Nightline line.

What's in the box

• UHC filter, unmounted 31 mm glass
• Protective plastic sleeve
• Padded pouch

Compatibility notes

• Designed for 31 mm unmounted filter holders and cells; it does not thread.
• Most effective in telescopes of 100 mm aperture and larger.