These defects become manageable at large focal ratios — most Schiefspieglers use f/15 or longer, which tends to restrict useful observation to the Moon and planets.
這些缺點在長焦比的望遠鏡上很容易處理－多數Schiefspiegler的焦比是f/15或更大，往往限制了只適用於月球和行星的觀測。