Sky watcher startravel 102t 102mm 4 f500 short tube achromatic refractor optical tube assembly the compact sky watcher startravel series are two element air spaced multi coated objective achromatic refractors and are well proven performers for rich field views of star fields clusters nebulae bright galaxies planets the moon and the sun with correct safety filtering as well as giving excellent terrestrial views these wide field short tube telescopes are also highly portabl