1. Optolong Clear Sky Filter Introduction

• A screw on filter with the easiest installation way like UV filter.
• Supress light pollution to make the night sky clearly.
• Enhance the contrast of images.
• To bring up the colors, fascinating experience.

2. Coating Technology

·Multi-layers anti-reflection coating
·Non-cementing optical substrate coating
·Optolong L-Pro filter adopts precision coating based on Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL(central wavelength) no deviation affected by temperature change.
·Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band.

Optolong 77mm Clear Sky Round Mounted Filter

The Clear Sky Filter is Optolong's newest light pollution filter. This filter is specifically designed to eliminate wavelengths responsible for artificial light pollution, such as Na and Hg light pollution. As shown in the photos above, this filter dramatically increases contrast and prevents excess light from reaching your camera sensor. With the Optolong Clear Sky filter, there is no wavelength shifting or gradient images. You are left with a true-color, high-contrast image.

Housed in a round 77mm CNC-machined cell, the Clear Sky filter can be threaded directly onto the front of your camera lens, like a UV lens. The filter itself is made of premium optical glass for quality you can see.

Optolong Clear Sky Filter Performance 

I. The Milky Way on the land of snow, imaged by 拂晓_718 (China)

Camera：Canon 5DS modified
Lens：Canon 35mm f/1.4 II
Filter：Optolong Clear Sky
Sky: f2.8 240s iso640
Land: f2.8 90s iso2000

II. Milk Way by Yuri Beletsky who used Optolong Clear Sky

III. Stone Forest under the Milk Way by Yule俞乐

Stone Grotoes 

by Optolong Clear Sky 

IV. Summer Milky Way at Cameron Highlands, imaged and processed by Sammax Chong (Malaysia)

Nikon D750,Samyang FishEye 12mm 

Optolong Clear Sky filter

ISO1600,30s,F2.8, 

8stacked

About Optolong

While Optolong is a relative newcomer to the astronomy industry, they are no strangers to optics and filters. Optolong is a division of Yulong Optics Company, a high tech company specializing in optical filter design and production. Their products include bandpass filters, flourescence filters, edge filters, longpass and shortpass filters, beam splitters, anti-reflection coatings, optical mirrors and, of course, astronomical filters.

Established in 1999 and based in Kunming City, China, Optolong/Yulong provides nearly 2000 types of optical filter coatings annually to customers worldwide in a wide variety of industries and applications.