Brightwell Dawnline light pollution filter 2 in, observatory grade

Specifications

Description

The Dawnline light pollution filter 2 in is a broadband filter in a 2 in threaded cell. It reduces transmission of the strongest emission lines from older street lighting, including the sodium line near 589 nm, while passing a wide portion of the visible spectrum. Stars and deep-sky objects keep a close approximation of their natural color, with a moderate loss of overall brightness.

Sky glow from artificial lighting does not always come from narrow lines, so the effect of this filter depends on the type of lamp near your observing site. It gives the greatest improvement under low-pressure sodium and mercury-vapor lighting. Under modern white LED lighting, whose spectrum is broad and continuous, the improvement is smaller. By reducing the background glow, the filter raises contrast, so the nebula itself does not become brighter. Under suburban skies, faint galaxy arms and the outer edges of large nebulae can become easier to trace.

Good targets include the Andromeda Galaxy, the Pleiades, the Double Cluster, and the Orion Nebula. Emission nebulae respond more strongly to narrowband filters such as UHC or OIII, which block more of the background, so this filter suits broadband targets. The filter dims the view, and it is most useful in telescopes of 6 in aperture and larger under moderately light-polluted skies.

The filter threads into 2 in eyepieces, 2 in diagonals, and 2 in filter adapters with M48 x 0.75 threads. Handle the glass by the cell edges and store it in its case when not in use, since contact with other optics can scratch the coatings.

About this configuration

This listing covers one configuration of the Brightwell Dawnline light pollution filter 2 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 Dawnline 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 plastic case is light and stacks with other filter cases in an accessory box. 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 2 in threaded cell
• Plastic storage case
• Test report with measured transmission curve
• Plastic storage case

Compatibility notes

• Threads into 2 in eyepieces, diagonals, and filter adapters (M48 x 0.75).
• Most effective in telescopes of 6 in aperture and larger under light-polluted skies.