The William Optics GuideStar 61 with the patented Bahtinov Mask Cover has been created to have the best combination of versatility and portability of every instrument they've ever offered. It produces fine, sharp images when paired with any DSLR camera for astrophotography or wildlife photography. The GuideStar 61 is useful for both visual applications and lunar photography when used with a separately sold Field Flattener 61 as it has a large image circle. This APO refractor is a superb instrument you'll be able to appreciate for many years to come!
Compared to the older FPL-51 ED glass, the FPL-53 glass employed by the objective lens has a distinct advantage. ED and SD glass dispersion plays a crucial role in determining overall color correction. "Partial dispersion" of a specific glass is measured by the Abbe Index number. Pure fluorite has the highest partial dispersion of any material at about 95 V. The partial dispersion of FPL-53 glass is extremely close to this, so close in fact that FPL-53 glass has been referred to as synthetic fluorite.
Superior FPL-53 glass material, the most expensive glass currently available, lets designers at William Optics obtain the finest color correction.
When you purchase a telescope from William Optics, you can be assured that your instrument was tested on their Interferometer. Furthermore, each telescope is individually star tested by William Optics professionals to guarantee the ultimate in optical quality.