Orion’s 120mm f/5 Refractor Telescope Optical Tube, which I will refer to for the rest of the article as the 120ST, has been around since the 1990s when they introduced their low-cost fast achromatic refractor line made by Suzhou Synta in China – this line also included the (sadly-discontinued) ShortTube 80 and the far less popular ShortTube 90.
In addition to being available as an optical tube, the 120ST is sold with Orion’s AstroView EQ mount for a convenient, portable and upgradeable complete observing package. An identical, rebranded and recolored optical tube is also sold with a lightweight alt-azimuth mount, erecting prism and 50mm finderscope as the Sky-Watcher StarTravel 120 AZ3.
The 120ST is a 120mm (4.72”) f/5 achromatic doublet refractor. Being a large f/5 achromat, there is quite a lot of chromatic aberration displayed on the Moon, planets, and bright stars. This scope is really meant for low-power, wide-field deep-sky viewing, and not much else. However, images at high and moderate magnifications of the Moon and planets are acceptable for the casual observer. Although they have severe chromatic aberration, the optics in the 120ST I used were certainly at least diffraction-limited, perfectly acceptable if not above average for ...