The filter has the dimensions of 10x 10cm, weighs 47.5gr and is 2mm thick, so it matches the filter holder of the same company. It is made of anti-reflective glass and allows to eliminate the noise due to artificial lights (i.e. the yellow part that appears at the bottom in the photographs of the Milky Way, due to the artificial lights of the city). The difference without the filter is remarkable, in fact even with a good post production process, the artificial light remains, while with the filter it is completely cut off. In the case of long exposures for the Milky Way, the amount of light captured by the sensor decreases slightly but the raw output is rich in information and allows you to recover the Milky Way and all the starry sky. It is possible to remedy this (i.e. capture more light) by using a star tracker or by taking more shots (in my case, without star tracker, with a f2.8 at 11mm, the maximum time for not obtaining the movement of the stars is 30 seconds). Even in the city it does its job by eliminating that yellowish gradient in the sky and bringing out the beauty of the night lights.