Astrophotographically optimized lens telescopes (astrographs) consist either of primary optics, combined with a flattener or reducer, or of multi-part (4 to 6 lens) optical designs that enable optimal geometric and chromatic correction. The focal ratio is very short (mostly f / 3.5 - f / 5.6), which shortens the exposure times.
The apochromatic refractor with 130 mm aperture and 910 mm focal length offers an image free of chromatic aberration and also allows astrophotography with all common correctors.