Also, the bottom of a focuser tube that protrudes into the light path can throw a big spike. Mirrors on three point supports that are flexing will usually present diffraction rings that are somewhat triangular shaped, rather than perfectly round. If so, then the mirror cell may be at fault. An oddly shaped diffraction ring may indicate that the mirror is being held too tightly pinched at one or more spots. If there is one big spike or a bright lane of distortion reaching out across an otherwise round diffraction pattern, you could have air currents in the tube.
Good eyepieces make a significant contribution to image quality.
Reasonable cost Some very good eyepieces meet only two or three of these, but if cost is no object, then you can easily find an eyepiece that meets the first four criteria. But they don t show any more detail than some simpler and less expensive designs, particularly the Orthoscopic, which has been around for many years and is often regarded as the best choice for planetary observing. Because there are just four optical elements, the throughput of light is greater than in some complex designs with up to nine elements. Ultrascopic and the Celestron Ultima are reasonably priced eyepieces of basically similar design that also do a fine job. Tele Vue eyepieces are expensive, but you can t go wrong with any of their products.