The FSQ series telescopes are designed with the Astro-imager in mind. Featuring a four-element lens system made with superb ED glass the FSQ produces a virtually flat field across a large image circle. In models other than the FSQ series, the image circle is defined as the circle in which light intensity is 60% or greater. However, because of the outstanding performance of the FSQ series, for these models, the image circle is defined as the area where star images are 30 microns or less.
In all FSQ telescopes, the light intensity across the image circle is greater than 70%. The FSQ-85ED and FSQ-106EDX4 each contain 2 ED elements. The FSQ-130ED contains 3 ED elements. While ideal for astrophotography, these telescopes also make outstanding visual instruments.