Introducing the William Optics GT81iv Refractor Telescope

We provide an introduction to the new William Optics Gran Turismo 81 (GT 81) 3-element APO refractor (478 mm focal length) and the new adjustable-length field flattener and focal reducer, the William Optics FLAT6Aiii (reduces the focal length to 384 mm). The first night out with the new scope is used to dial in the correct length for the FLAT6Aiii to provide a flat field and to identify focuser backlash and fine and coarse focuser step size s using the  Pegasus Astro FocusCube 2 and the Bahtinov focus error metric.