Optolong new item-Clear Sky Filter,front facing 77mm,no dark-corner.
Optolong Clear Sky Filter is the first new item in 2017 from Optolong Optics Co.,Ltd.Clear Sky blocks the city Na and Hg light pollution so that improve contrast effectively.The main point of this filter that differ with other filter, its front facing,77mm, you can twist it in front of camera lens directly like UV lens. More important is its performance, no wavelength shifting , no color gradient through the images(result).
This type suits for any lens what UV lens fit.
Below images are from famous astrophotographer Vincent Cheng-不动明王( HongKong) on January 9th.2017.
The left one without filter, the middle image with Optolong Clear Sky Filter single JPEG frame, the right image with Optolong Clear Sky Filter 62frames stacked.