Pellucid Clearwater UHC nebula filter 2 in, observatory grade

Specifications

Description

The Clearwater UHC is an ultra-high contrast nebula filter in a 2 in brass cell with an M48 x 0.75 thread. It passes a band about 28 nm wide that covers the doubly ionized oxygen lines at 496 and 501 nm and the hydrogen-beta line at 486 nm, and it also passes the hydrogen-alpha line at 656 nm. Most other visible wavelengths are blocked, including much of the broadband glow produced by artificial lighting.

Emission nebulae concentrate their light at these discrete wavelengths, while the sky background spreads its glow across the spectrum. By blocking the background and passing the nebula's light, a UHC filter increases the contrast between the two. The nebula itself does not become brighter, but the surrounding sky becomes darker, which allows you to see faint outer structure that would otherwise be lost in the glow.

Useful targets include the Orion Nebula, the Lagoon and Trifid nebulae, the Swan Nebula, the North America Nebula with a wide-field instrument, and planetary nebulae such as the Ring and the Dumbbell. Under moderately dark skies, the filter works best in telescopes of 100 mm aperture or larger, where the wide field of a 2 in eyepiece suits extended nebulae. Galaxies, star clusters, and reflection nebulae emit across a broad range of colors, so on those targets the filter mainly dims the view. Stars also take on a slight greenish tint because the passband sits in the blue-green part of the spectrum.

The cell threads onto 2 in eyepieces and 2 in filter adapters, so confirm that the thread matches your accessory before use. The glass carries a multi-layer interference stack on one side and an anti-reflection layer on the other. Keep the filter in its padded case when it is not in use to protect the coatings from dust and abrasion.

About this configuration

The Pellucid Clearwater UHC nebula filter 2 in is offered in several configurations, and the notes below describe what this particular one includes. 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 Clearwater 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.

The filter ships in a clear plastic case that keeps dust off the glass between sessions. This is the 2024 edition, which revised the cell knurling and the case insert of the Clearwater line. The transmission figures in the specifications apply to every configuration of the Clearwater line.

What's in the box

• UHC filter in 2 in threaded brass cell
• Padded storage case
• Test report with measured transmission curve
• Plastic storage case

Compatibility notes

• Threads onto 2 in eyepieces and 2 in filter adapters (M48 x 0.75).
• Most effective in telescopes of 100 mm aperture and larger.