A group of dedicated amateur astronomers has recently tested the new Orion refractor telescope. They found that it allowed them to see planetary details clearly, while the features appeared blurred through their 10-inch (approximately 25-centimeter) Schmidt-Cassegrain telescopes. Despite the 10-inch telescopes having larger apertures and gathering more light than the 5-inch (approximately 13-centimeter) Orion, the astronomers concluded that any serious amateur astronomer should choose the Orion for planetary observation. Which one of the following most seriously weakens the argument?