Brightwell Dawnline light pollution filter 2 in

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 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. The standard coating is applied to the filter side of the glass, with a single anti-reflection layer on the back.

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 Dawnline line. 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 2 in threaded cell
• Plastic storage case
• Padded pouch

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.