Aurel Clarion UHC filter 31 mm, observatory grade

Specifications

Description

The Clarion UHC filter is an unmounted 31 mm round nebula filter for filter wheels and filter drawers. Its 28 nm passband covers the hydrogen-beta and doubly ionized oxygen lines, and a second passband transmits the hydrogen-alpha line in the red.

Used with a color camera, the Clarion UHC records emission nebulae with high contrast against a darkened sky. The combination of a blue-green and a red passband keeps a natural-looking balance between hydrogen and oxygen regions, so nebulae such as the Lagoon, the Trifid, and the Orion Nebula show their familiar colors.

Under light pollution and moonlight, the filter makes it possible to image emission nebulae on nights that would otherwise be too bright. It works with one-shot color cameras and, in a filter wheel, alongside other filters for monochrome cameras.

The filter is less suited to galaxies and star clusters, which shine across the spectrum. For those targets, use a broadband filter or no filter. Stars recorded through the Clarion UHC appear with a slight color shift, which processing can correct.

The 31 mm size fits filter wheels designed for unmounted 31 mm filters and covers smaller camera sensors. Check your sensor size and filter wheel spacing before you choose.

The glass has a multi-layer interference coating on one side and an anti-reflection coating on the other, which keeps halos around bright stars small in stacked images.

The Clarion UHC suits imagers with small sensors who want to capture emission nebulae from suburban sites with a single filter.

About this configuration

This listing covers one configuration of the Aurel Clarion UHC filter 31 mm, defined by its grade, coating, case, and edition year. 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 Clarion 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. This is the 2023 edition of the Clarion line, the earliest version that is still listed in the catalog. The transmission figures in the specifications apply to every configuration of the Clarion line.

What's in the box

• UHC filter, unmounted 31 mm round
• Plastic storage case
• Test report with measured transmission curve
• Padded pouch

Compatibility notes

• Fits filter wheels and holders that accept 31 mm unmounted filters.
• Covers sensors up to about 4/3 in size in typical filter wheel spacing.
• Pairs with one-shot color cameras and with monochrome cameras in a filter wheel.