These are superb and only available here at Surplus Shed! Glass, air-spaced achromatic optics, multi-coated! 153mm clear diameter with a focal length of 1200mm making this an f/7.8. Mounted in an aluminum barrel. The lens elements can be easily removed (if you want) by unscrewing the retaining ring. An incredible price that may not last long!! NEW! This objective will make a quality refractor scope or an awesome binocular telescope if you get two. The larger the diameter of the objective, the more light that gets captured and the more you will be able to see.