High-quality, apochromatically corrected optics with small opening ratio.
Apochromatic refractors (ED APOs) belong to the upper class of refracting telescopes. They can focus three colors (RGB) in the same point by the integration of correction lens(s) (ED elements). This makes the image virtually free of color errors. A special reducer-lens combination reduces the aperture ratio by a factor of 0.75x.