Aurel Clarion H-beta filter 2 in

Specifications

Description

The Clarion H-beta is a hydrogen-beta line filter in a 2 in threaded cell. Its 24 nm passband, centered on 486 nm, is wider than that of most H-beta filters, which lets through more light while still darkening the sky background substantially.

The wider passband makes the Clarion H-beta easier to use in medium telescopes. In a 200 mm Dobsonian under dark skies, it can show the glow of IC 434 behind the Horsehead Nebula and the brighter parts of the California Nebula. In large telescopes, the extra light makes these objects easier to hold with direct vision.

The trade-off is contrast. A wider passband lets through more sky background than a narrow filter, so under bright suburban skies the effect is smaller. The Clarion H-beta works best at rural and dark sites.

Use a low-power eyepiece with the filter, so the exit pupil is large and the view stays bright. Find the target without the filter first, then add it, since the filter dims field stars along with the background.

The 2 in cell threads into eyepieces, diagonals, and filter wheels. It can stay in a 2 in diagonal while you change eyepieces, which is convenient for comparing views at different magnifications.

The glass is float glass with a multi-layer interference coating on one side and an anti-reflection layer on the other. Clean it with a blower and, if needed, lens fluid on a soft tissue.

The Clarion H-beta suits observers who want to try the Horsehead and the California Nebula without the cost of a narrow-band filter made on polished glass.

About this configuration

This listing covers one configuration of the Aurel Clarion H-beta filter 2 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. Hard-sputtered layers keep their passband stable over time, which matters if you compare images taken years apart.

A padded pouch is easy to open with cold fingers, which helps when you swap filters during a session. The 2025 edition keeps the same transmission figures as the earlier years of the Clarion line. The transmission figures in the specifications apply to every configuration of the Clarion line.

What's in the box

• H-beta filter in 2 in threaded cell
• Plastic storage case
• Padded pouch

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter wheels (M48 x 0.75).
• Most effective in telescopes of 200 mm aperture and larger under dark skies.