Aluminum 102mm DoubletFeatures The Explore Scientific AR Series telescopes are classic air spaced, crown and flint, doublet achromatic f 6. 5 refractors with a superior class optical figure. Whether you choose the AR102 (4"), AR127 (5") or AR152 (6") model, you will be impressed by the stunning images revealed to you at the eyepiece, and all at a small fraction of the price you'd pay for a comparably sized apochromat refractor. Designed to handle the rigors of public star