Aurel Dusk Ridge light pollution filter 1.25 in

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

All configurations of the Aurel Dusk Ridge light pollution filter 1.25 in share the same filter glass design; the options change the grade, the coating, and the case. 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 plastic case is light and stacks with other filter cases in an accessory box. The passband in the 2024 edition matches the other years; the changes concern the housing only. Check the size in the specifications against your eyepiece barrels, star diagonal, or filter wheel before you choose.

What's in the box

• Light pollution filter in 1.25 in threaded cell
• Plastic storage case
• Plastic storage case

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.