"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|Freedom from ghost images, even when stacked|Striae-free substrates are polished parallel to within 30 seconds of arc to avoid wedge errors|Finest 7-layer hard multi-coatings on both faces feature 0.25% residual reflections|Extremely high transmission results in maximum contrast and isolation of planetary details, even with smaller telescopes|Efficiencies of the bandpass filters (Green) achieve 70%|Carefully designed spectral characteristics. Filters may be stacked without image degradation or ghosting, in order to provide even narrower passbands, or combine with any of the other Baader filters for interesting possibilities|No reduction in sharpness, even at high magnifications or when using the filter far ahead of the focal plane|With the 2" size, only one filter is needed for binoviewing. Only Baader colored filters have the optical quality necessary for use this far ahead of the focal plane"