The Optolong L-eXtreme F2 filter is specially designed for bright (F2, F3) telescopes such as the RASA telescope. It is mainly for use with colour astronomy cameras and DSLR cameras. It is essentially two narrow-band filters in one: it has one passband optimised for the H-alpha wavelength range (656.3 nm) with a bandwidth of 7 nm and another in the OIII range (500 nm.) Most diffuse nebulae are "brightest" in these two ranges. The two narrow transmission ranges filter out light pollution or distracting moonlight, making them uniquely effective in reducing background light for urban astrophotographers
.The filter has a narrow design, only 5 mm thick (without thread). Made of high quality Schott glass, its surface is coated with multiple layers of anti-reflective coatings.
The Optolong l-eXtreme F2 filter offers a real alternative for those who have a color camera but want to get shots similar to narrow-band photos.