These four element oculars feature the classic symmetrical doublet design which is very famous for field correction (Image view is very sharp from the centre to the edge). Multi-coated and black coloured edges of lenses deliver a crisp, high contrast image (specially priced for Planetary viewing). It’s field of view is 52° panorama for F/ratios as low as F/4.5. (44° for the 40mm Supper Plossl). These eyepieces are excellent performers with telescopes of all types. It also has a thread for photo-visual filters.