Nice mounted air-spaced achromatic glass telescope objective. Both elements are coated with an AR coating. Clear lens diameter of 90mm with a focal length of 500mm (F/5.5). Front barrel diameter is 90mm (ID) and 99mm (OD), rear barrel is 100mm (ID) and 105mm (OD). The entire assembly is 63mm long and flange has a diameter of 116mm. These are brand new and will make a great wide field scope!