Pellucid Glasshaven light pollution filter 1.25 in, observatory grade

Specifications

Description

The Glasshaven light pollution filter is a broadband filter in a 1.25 in threaded cell. It transmits most of the visible spectrum while blocking part of the light emitted by sodium and mercury vapor street lamps, which contribute much of the glow over towns and cities. Its peak transmission of about 88 percent keeps the view bright enough for stars, planets, and the Moon, so you can leave it in place for general observing rather than switching to a different filter for each target. The filter is intended for use under suburban and urban skies, where the sky background is brightest.

Light pollution adds a diffuse glow that spreads across the sky background and lowers contrast for faint objects. By reducing the wavelengths that make up that glow, the filter darkens the background more than it dims extended objects that emit across a wide range of colors. Galaxies, globular clusters, and open clusters often show more structure under suburban skies with this filter in place. Emission nebulae respond differently, because a UHC or OIII filter usually gives more contrast on those targets than a broadband filter does, and you may find it useful to carry both.

Stars and planets keep their natural colors, although the filter reduces the total light reaching your eye, so faint stars and dim detail will appear slightly fainter than in an unfiltered view. Use it with a telescope of 100 mm aperture or larger when you are looking for faint outer structure in galaxies. Allow your eyes about 15 minutes of dark adaptation after you change the filter, and keep the glass clean, since dust and fingerprints can reduce contrast more than the filter itself does.

The filter threads into any 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal. Both faces of the glass carry an anti-reflection coating, which limits the light lost at each surface and reduces internal reflections.

About this configuration

All configurations of the Pellucid Glasshaven light pollution 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 Glasshaven 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.

The aluminum case protects the filter from crushing in a crowded accessory box. The 2023 edition uses the same coating design as later years, with small differences in the cell markings. The transmission figures in the specifications apply to every configuration of the Glasshaven line.

What's in the box

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

Compatibility notes

• Threads into 1.25 in eyepieces, diagonals, and filter wheels (M28.5 x 0.6).
• Suited to telescopes of any aperture, with the greatest effect under suburban and urban skies.