The Baader Planetarium FCFG-2 Green Bandpass Filter has a bandpass at 500 nm and is designed for 2" eyepieces. It has 70% transmission efficiency and is superb for bright planet and cometary details. It can be placed anywhere in the optical path without introducing astigmatism or other defects. Baader Planetarium astronomy filters by far supersede the mediocre quality of common "flame polished" color filters. A fine optical polish and 2 mm thick glass allows these filters to be inserted anywhere into the optical path without introducing astigmatism or other defects. For instance, they can be used in front of a binocular viewer without degrading the image in any way.Substrates are free of striae and plane-parallel polished to within 30 seconds of arc. This eliminates any double images or ghosting due to wedge errors in the glass. The filter cell features the largest clear aperture of any telescope filter on the market for complete freedom from vignetting at any focal length.The front "crown" incorporates milled notches, which makes handling and threading the filter an easy operation in the dark. All surfaces are treated with a 7-layer Multi-Coating, featuring a mere 0.25% residual reflection. It is the most elaborate coating ever applied onto amateur color filters, resulting in a filter free of any false reflections under any incident angle of light. Light is the hottest commodity for all planetary observation.Especially during high magnification work