Aurel Dusk Ridge light pollution filter 1.25 in, observatory grade

Specifications

Description

The Dusk Ridge light pollution filter is a broadband filter in a 1.25 in threaded aluminum cell. It transmits most of the visible spectrum across a band about 120 nm wide and reduces the intensity of the narrow emission lines produced by many outdoor lamps, including the 589 nm sodium doublet and the mercury lines near 546 nm and 436 nm. Because the passband is wide, stars keep their natural colors, and galaxies, star clusters, and reflection nebulae remain visible with only a modest loss of brightness.

Artificial lighting spreads some of its output across the spectrum and concentrates the rest in a few lines. Sodium and mercury vapor lamps emit most of their light at specific wavelengths, so a filter that removes those lines lowers the sky background without dimming the whole field. Under suburban skies, the background becomes darker and faint outlines of extended objects become easier to see. Under dark rural skies, the improvement is smaller. You will notice the greatest difference when the target sits low over a city, where sky glow is strongest.

Thread the filter into the barrel of a 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal, and keep the glass free of fingerprints and dust. Because the filter is broadband, it dims the view somewhat, so it suits targets where contrast matters more than brightness. Store it in its case when not in use to protect the coatings from abrasion and moisture.

About this configuration

This listing covers one configuration of the Aurel Dusk Ridge light pollution filter 1.25 in, 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 Dusk Ridge line, which suits imaging with long focal lengths. 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 2023 edition uses the same coating design as later years, with small differences in the cell markings. A filter does not make objects brighter; it darkens the sky background more than the target, which raises contrast.

What's in the box

• Light pollution filter in 1.25 in threaded cell
• Plastic storage case
• Test report with measured transmission curve
• Padded pouch

Compatibility notes

• Threads into 1.25 in eyepieces, diagonals, and filter wheels (M28.5 x 0.6).
• Useful in telescopes of any aperture, with the largest gains under urban skies.