Pellucid Spectra H-beta filter 1.25 in

Specifications

Description

The Spectra H-beta is a line filter in a 1.25 in threaded cell that passes a 9 nm band centered on the hydrogen-beta line at 486 nm. It is a specialized filter, used for a small number of nebulae that shine mainly in hydrogen-beta light and respond poorly to UHC and OIII filters.

The best-known target is the Horsehead Nebula in Orion, a dark cloud seen against the faint glow of IC 434. The H-beta filter darkens the sky enough to show the glow behind the Horsehead in telescopes of 250 mm aperture and larger under dark skies. Other targets include the California Nebula, IC 5146 (the Cocoon Nebula), and parts of the Orion Nebula.

Because so few objects benefit, many observers buy an H-beta filter only after they own a UHC or OIII filter. For the targets where it works, though, the difference can be large: a nebula that is invisible without the filter can become visible with it.

The narrow passband dims stars strongly, so finding the target before you add the filter helps. Large exit pupils work best: use a low-power eyepiece that gives an exit pupil of 5 to 7 mm.

The filter is made on polished optical glass with hard-sputtered coatings on one side and an anti-reflection layer on the other. The 1.25 in cell threads into eyepieces and diagonals.

In small telescopes, the dim view limits the filter's use. In a wide-field refractor with a low-power eyepiece, the California Nebula is a reachable target under very dark skies.

About this configuration

This listing covers one configuration of the Pellucid Spectra H-beta filter 1.25 in, defined by its grade, coating, case, and edition year. 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. The hard-sputtered coating resists scratches and humidity, so the filter tolerates cleaning better over the years.

The padded pouch protects the filter from knocks and fits in a jacket pocket at the telescope. This is the 2023 edition of the Spectra line, the earliest version that is still listed in the catalog. Check the size in the specifications against your eyepiece barrels, star diagonal, or filter wheel before you choose.

What's in the box

• H-beta filter in 1.25 in threaded cell
• Padded storage pouch
• Padded pouch

Compatibility notes

• Threads into 1.25 in eyepieces and diagonals (M28.5 x 0.6).
• Works best with low-power eyepieces that give an exit pupil of 5 to 7 mm.