Pellucid Glasshaven light pollution filter 1.25 in, premium 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

The Pellucid Glasshaven light pollution filter 1.25 in is offered in several configurations, and the notes below describe what this particular one includes. The premium grade uses polished glass with tighter flatness tolerances, which helps at high magnification. Premium grade filters are checked for the position of the passband before they leave the factory. 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 2023 edition of the Glasshaven line, the earliest version that is still listed in the catalog. 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
• Padded storage pouch
• Padded pouch

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.