Baader Semi-APO filter designed for achromatic refractor owners and removes most chromatic aberration effects in violet and yellow colors, leaving a natural full bar range. The high transmission of light and the already mentioned neutral color make it virtually unnoticeable in use. In fact, Semi-APO combines the characteristics of Baader Neodynium Moon & Skyglow (lunar - planetary) filters and slightly reinforced Fringe Killer (eliminating chromatic aberration), but removing much more violet.
It is noted that the image and contrast are sharpened, which is particularly evident when observing such planets as Mars or Jupiter.
The filter has been supplemented with UV / IR Cut coatings, which makes it cut off the infrared and ultraviolet band, increasing the resolution of the obtained images in the sky photography.
In total, it is the most powerful lunar - planetary filter from Baader's stables and the most recommended by us.
(measurements on the Varian Cary 100 spectrophotometer, July 2015)