Aurel Dusk Ridge UHC nebula filter 1.25 in, observatory grade

Specifications

Description

The Dusk Ridge UHC is an ultra-high contrast nebula filter in a 1.25 in threaded cell, designed for observers using Aurel Dobsonians and other visual telescopes with 1.25 in eyepiece barrels. Its passband is about 25 nm wide and sits in the blue-green part of the spectrum, covering the doubly ionized oxygen lines near 496 and 501 nm and the hydrogen-beta line at 486 nm, with a narrower response to hydrogen-alpha in the deep red. Most other visible wavelengths are blocked, including much of the orange and yellow glow from street and sodium lighting.

Emission nebulae radiate at these specific lines, while the sky background is spread across the spectrum. By suppressing the background and passing the nebula's light, the filter raises contrast without making the nebula brighter. Under moderately dark skies, you may see faint outer regions and dust lanes that remain hidden in an unfiltered view. Good targets include the Lagoon Nebula, the Trifid Nebula, the Eagle Nebula, the Crescent Nebula, and planetary nebulae such as the Ring and the Dumbbell. The effect is most noticeable in telescopes of 100 mm aperture or more, where the light gathered from faint nebulae is greater.

Galaxies, star clusters, and reflection nebulae emit across a broad range of wavelengths, so on those targets the filter only dims the view. Stars also take on a greenish tint because of the passband. Thread the filter into the barrel of any 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal, and seat it fully before observing. One side carries a multi-layer interference stack and the other an anti-reflection layer, which keeps stray reflections low in the light path.

Because it works on many emission and planetary nebulae, this filter suits observers who want a single accessory for deep-sky nebula work. Keep it in the supplied case when not in use to protect the coated surfaces from dust, moisture, and fingerprints, and handle it by the edge of the cell rather than the glass.

About this configuration

All configurations of the Aurel Dusk Ridge UHC nebula filter 1.25 in 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 Dusk Ridge 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.

A padded pouch is easy to open with cold fingers, which helps when you swap filters during a session. This is the 2024 edition, which revised the cell knurling and the case insert of the Dusk Ridge line. Check the size in the specifications against your eyepiece barrels, star diagonal, or filter wheel before you choose.

What's in the box

• Dusk Ridge UHC filter in 1.25 in threaded cell
• 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).
• Most effective in telescopes of 100 mm aperture and larger.