Brightwell Nightline UHC nebula filter 2 in

Specifications

Description

The Nightline UHC nebula filter 2 in is an ultra-high contrast nebula filter in a 2 in threaded cell. Its passband is about 25 nm wide and covers the doubly ionized oxygen lines at 496 and 501 nm and the hydrogen-beta line at 486 nm, while the hydrogen-alpha line in the deep red also passes. Most other visible wavelengths are blocked, including much of the glow from artificial lighting. The glass transmits about 90 percent of light within the passband.

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 itself does not get brighter, but the sky around it darkens, so faint outer regions can become visible. Comparing the view with and without the filter at the eyepiece shows how much of the surrounding nebulosity was hidden by sky glow.

Good targets include the Orion Nebula, the Lagoon and Trifid nebulae, the Swan Nebula, the Veil Nebula, and the North America Nebula in a wide-field telescope. Planetary nebulae such as the Ring and the Dumbbell also respond well. The benefit is clearest in telescopes of 100 mm aperture or more under moderately dark skies, where the wide field of a 2 in eyepiece takes in the larger emission regions at once.

A UHC filter does not help with galaxies, star clusters, or reflection nebulae, which shine across a broad range of colors. On those targets it simply dims the view. Because the passband sits in the blue-green part of the spectrum, stars appear greenish through the filter. The filter threads into the 2 in filter cell of a diagonal or the nosepiece of a 2 in eyepiece, and the glass carries an interference coating on one side and an anti-reflection layer on the other.

About this configuration

The Brightwell Nightline UHC nebula 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. With anti-reflection layers on both sides, less light bounces between the filter and the eyepiece or camera sensor.

A plastic case is light and stacks with other filter cases in an accessory box. This is the 2023 edition of the Nightline line, the earliest version that is still listed in the catalog. The transmission figures in the specifications apply to every configuration of the Nightline line.

What's in the box

• UHC filter in 2 in threaded cell
• Plastic storage case
• Plastic storage case

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter wheels (M48 x 0.75).
• Most effective in telescopes of 100 mm aperture and larger.