"Less is more!" Better a few filters with high optical performance produced for astronomical observations than whole mountains of filters with mediocre quality.
The Baader colour filters are carefully prepared for amateur astronomical interests. The glass are coplaner fine optically polished. These filters exceed the quality of the usual "raw polished" (hot flamed) coloured glass filters.
Because they are fine optically polished, these filters can be at any point in the mean path - far ahead of the focal point (for example, in front of a binocular approach!) without causing defects (astigmatism) or to degrade the image otherwise in any way!
The parallelism of the optical surfaces is excellent with 30 arcseconds. Double images are absolutely excluded. For each filter colour, the transmission curve is supplied as a measurement protocol.
Colour filters are often identified with a Kodak Wratten number (W-point). Baader colour filters were collected by astronomical experience and correspond to the respective wavelength range following filter by Wratten nomenclature: Baader-red filter ≅ W25, Baader-Orange filter ≅ W21, Baader-yellow filter≅ W12, Baader-green filter≅ W58, Baader-light blue filter ≅ W80A, Baader-dark blue filter≅ W38A
These filters are screwed into the filter thread of eyepieces or planetary imaging cams (Skyris). A thread at either end of the filter allows the filters to be combined with each other or with other filters (for example with a Baader UV / IR infrared cut filter).
Developed by Baader Planetarium the coating is a 7-layer broadband coating with extremely low residual reflection. The term "Group" indicates that the respective most effective anti-reflection layer system was calculated for each type of glass of the filter.
This means that the anti-reflection layers of different colour filters are different. They are calculated to provide the maximum for the respective filtered colour transmission values.
Both sides of the filter are coated with 7-layer AR coating with only 0.25% residual reflection per surface. This is the most that has ever been provided for colour filters. The filter discs are screwed into the blackened aluminium frames and are delivered within a filter. Each filter is designed for multiple applications.