The new William Optics Zenithstar 126, at a stowed length of 970mm, is a reasonably compact telescope for its aperture. The relatively short focal length, particularly in conjunction with the optional 0.8X focal reducer (yielding f/6.2), delivers wide visual fields and deep-sky astro-images. At the same time the Ohara FPL-53 objective yields excellent control of false color for high power work.
The FPL-53 substrate used in its objective has dispersion characteristics not much different from that of the much vaunted fluorite crystal, and so is termed a synthetic fluorite. This permits the employment of a fairly fast f/7.7 while delivering superb chromatic aberration suppression.
The generously large illuminated circle of 43mm covers a full-frame DSLR camera sensor, a diagonal angular coverage of just some 2.5° (nearly 3.2° at f/6.2). And the guaranteed Strehl ratio of 0.92 or better assures diffraction limited performance.
For the wide field astro-imager particularly, William Optics offers an optimised 0.8X focal reducer/flattener, yielding a fast f/6.2. Other of their field flatteners are compatible when adjusted appropriately, if one does not wish to shorten the focal length. Aiding in the determination of when to check for focus drift, the focuser knob has a handy built-in thermometer. Critical focus is assessed using the included Bhatinov mask cover, and is afforded by the co-axial 10:1 fine focus knob. The sturdy 3.3" rack-and-pinion focuser employs a helical rack that will not slip under heavy loads, nor will the focuser sag or otherwise shift.