Baader glass substrates are of true optical quality. Most other filters are merely made from raw flame-polished, "optically flat", or sometimes use a top quality commercially polished filter glass which is fine for camera filters, but can result in wavefront deformations that damage image sharpness and contrast when used with telescopes. Baader Planetarium filters are made from striae-free substrates, and actually fineoptically polished flat to within 1/4 wave accuracy over the entire surface, plane parallel to within 30 seconds of arc!
We are also happy to offer the Baader 2" Blue Dielectric Coated Filter as an internal Energy Rejection Filter for use with Daystar rear mounted solar Calcium H-Line filter systems. We have tested the filter with refractors up to 152mm and found the resulting filtered light to be cool and safe for use as an internal ERF while maintaining a high level of optical quality for the optical system. Please contact us for further details.
