High quality optical Prism inside rather than a mirror which makes your image clear and sharp More comfortable viewing orientation as you observe from above, filter thread for any 1.25 inch filter; accepts standard 1.25 inch eyepieces Protective coating on the mirror to ensure a long life; metal barrel for secure seating in the focuser This is a great diagonal for daytime terrestrial use and night time astronomy applications for telescopes or spotting scopes 1.25 inch 45 degree mirror star diagonal for refractor telescopes with 1.25 inch connector and not recommended for reflectors Whether it's the Moon, Jupiter or a beautiful nebula - in order to enjoy observing at the telescope you should always be comfortable. In many telescopes, that is only possible by using a star diagonal - which directs the image upwards by 45.This Astromania star diagonal has a 1.25" metal barrel. The chrome finish not only looks good, but is also practical, as the star diagonal always remains firmly attached to the focuser. The clamping screws lock the barrel firmly in place without scoring the nosepiece, as is the case with many cheaper products. In short - this barrel will keep your star diagonal in condition for virtually forever.The mirror has had everything that is possible optimised, within this price range, to ensure you enjoy a bright image - even at higher magnifications. It is the link between your eye and the telescope - and is hence just as important.Sometimes you do not want to have to re-install a filter every time you use a new eyepiece. Perhaps you might want to observe the Moon today with a range of eyepieces - but with the same filter? That is also possible due to the filter thread provided in the star diagonal.