Brightwell Nightline UHC nebula filter 1.25 in, observatory grade

Specifications

Description

The Nightline UHC is an ultra-high contrast nebula filter in a 1.25 in threaded cell. 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. It blocks most other visible light, 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 faint outer regions become visible.

Good targets include the Orion Nebula, the Lagoon and Trifid nebulae, the Swan Nebula, the North America Nebula in a wide-field telescope, and planetary nebulae such as the Ring and the Dumbbell. The effect is strongest in telescopes of 100 mm aperture or more and under moderately dark skies.

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. It also makes stars appear greenish, since the passband sits in the blue-green part of the spectrum.

The filter screws into the barrel of any 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal. The glass is coated on one side with the multi-layer interference stack and on the other with an anti-reflection layer.

For many observers, a UHC filter is the first nebula filter to buy, because it works on a wide range of emission and planetary nebulae.

About this configuration

All configurations of the Brightwell Nightline UHC nebula filter 1.25 in share the same filter glass design; the options change the grade, the coating, and the case. The observatory grade comes with a measured transmission curve for the individual filter in the box. Observatory grade glass has the tightest flatness tolerance in the Nightline line, which suits imaging with long focal lengths. With anti-reflection layers on both sides, less light bounces between the filter and the eyepiece or camera sensor.

An aluminum case with a foam insert keeps the filter safe during travel to a dark site. This is the 2024 edition, which revised the cell knurling and the case insert of the Nightline line. A filter does not make objects brighter; it darkens the sky background more than the target, which raises contrast.

What's in the box

• UHC filter in 1.25 in threaded cell
• Plastic storage case
• Test report with measured transmission curve
• Aluminum storage case

Compatibility notes

• Threads into 1.25 in eyepieces, diagonals, and filter wheels (M28.5 x 0.6).
• Most effective in telescopes of 100 mm aperture and larger.