Aurel Lodestar H-beta filter 31 mm, observatory grade

Specifications

Description

The Lodestar H-beta filter is a narrowband nebula filter for observers who want to isolate the hydrogen-beta emission line at 486 nm. It is supplied as 31 mm unmounted round glass with a bandpass of about 12 nm, centred on the hydrogen-beta line, and a peak transmission of roughly 88 percent. Because the glass has no cell, you mount it yourself in a 31 mm retaining ring, a filter holder, or a drop-in slot in a filter wheel.

Hydrogen-beta emission is considerably fainter than hydrogen-alpha, so this filter shows its effect most clearly on bright emission regions such as the Orion Nebula and the Rosette Nebula, and in telescopes of moderate to large aperture. Under moderately dark skies, the narrow band suppresses the sky background across most of the visible spectrum, which raises the contrast of the nebula's own glow. Many observers pair it with an OIII filter, which passes the oxygen lines at 496 and 501 nm, so that the two filters together cover more of the emission spectrum in a single session.

The filter does not help with galaxies, star clusters, or reflection nebulae, which emit across a broad range of wavelengths or reflect starlight. On those targets it mainly dims the view. Stars are strongly reduced in brightness, since most starlight falls outside the passband. Handle the glass by its edges, keep the coated faces free of fingerprints, and store it in a dust-free sleeve when it is not in use.

The glass is coated on one face with a multi-layer interference stack that defines the passband and on the other face with an anti-reflection layer. Check the rim for any orientation marking before you mount the filter.

About this configuration

All configurations of the Aurel Lodestar H-beta filter 31 mm 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 Lodestar line, which suits imaging with long focal lengths. 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. The 2023 edition uses the same coating design as later years, with small differences in the cell markings. The transmission figures in the specifications apply to every configuration of the Lodestar line.

What's in the box

• H-beta filter, 31 mm unmounted glass
• Protective paper sleeve
• Test report with measured transmission curve
• Padded pouch

Compatibility notes

• Requires a 31 mm mounting ring, filter holder, or filter wheel slot, as the glass is not mounted.
• Most effective in telescopes of 100 mm aperture and larger.