Pellucid Spectra UHC nebula filter 2 in, observatory grade

Specifications

Description

The Spectra UHC is an ultra-high contrast nebula filter in a 2 in threaded cell, made on polished optical glass. Its 22 nm passband covers the hydrogen-beta and doubly ionized oxygen lines between 486 and 501 nm, with peak transmission of about 95 percent, and it also passes the hydrogen-alpha line.

The narrow passband darkens the sky background strongly while keeping most of the light from emission nebulae. Under suburban and rural skies, the Spectra UHC shows the outer loops of the Orion Nebula, the dark lanes in the Lagoon Nebula, the Eagle Nebula around M16, and the full shape of the North America Nebula in wide-field telescopes.

The polished substrate keeps the filter optically flat, so it adds no visible distortion at high magnification. That matters when you observe small planetary nebulae, such as the Cat's Eye or the Eskimo, at 200x or more, where the filter can show shells and structure around the bright inner regions.

The multi-layer coating is hard-sputtered on one side, with anti-reflection coatings on both faces. The 2 in cell threads into eyepieces, diagonals, and filter wheels with the standard M48 thread.

Like all nebula filters, the Spectra UHC dims stars and gives them a greenish tint, and it does not help with galaxies or star clusters. Keep it for emission and planetary nebulae, and observe other targets without it.

The 2 in size suits telescopes with 2 in focusers, where it can stay in the diagonal while you change eyepieces.

About this configuration

The Pellucid Spectra 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 Spectra line, which suits imaging with long focal lengths. The standard coating is applied to the filter side of the glass, with a single anti-reflection layer on the back.

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 Spectra line. The transmission figures in the specifications apply to every configuration of the Spectra line.

What's in the box

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

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter wheels (M48 x 0.75).
• Most effective in telescopes of 150 mm aperture and larger under rural or suburban skies.