The Baader Semi APO filter combines both the Neodymium Skyglow and Fringe Killer filters into one. The result is a filter that drastically increases contrast and cuts out the blue and NIR ends of the spectrum, eliminating false colour present in many achromatic refractors. As most budget refractors are not very well corrected at these wavelengths, this filter allows you to make the most of the optics without changing the overall colour of the image. The optical surface is fine-optically polished so that there is no loss of sharpness at high magnifications, even when the filter is positioned far in front of the focal point. They can even be put in front of a binoviewer without introducing astigmatism. The Fringe Killer coating is similar to a minus-violet filter, except it does not alter the colour balance. To achieve this, the filter has plasma-enhanced dielectric coatings with almost 50 layers on each side. In addition to this, the is Baader's 7-layer Phantom Group anti-reflection coatings. Note: Baader Neodymium filters are only 1mm thick, so will change backfocus requirements when used with more common 2-3mm thick imaging filters. This is because the absorption of the extra neodymium ions would be too great in thicker glass, which would lead to less brilliance in the resulting image. Available in either 1.25" or 2" mounted. The filter cell is threaded on both ends so that multiple filters can be stacked. All Baader filters (excluding 100 x 100mm) come in stackable labelled filter boxes which can be attached to each other to form a sturdy filter library. Specifications Transmission range Multiple bands - see spectrum image Type of filter Bandpass Usage Contrast enhancement, colour correction, IR-Cut AR-coating Phantom Group coating, planeoptically polished Filter thickness 1 mm (without cell), 6 mm with cell Filter size 1.25" / 2" mounted SKU BA2458398 (1.25"), BA2458399 (2")
