>>This actually matters a lot, because other than this, mirrors are superior to refractive glass lenses in almost every way No. Reflective designs (mirrors) ar

>>This actually matters a lot, because other than this, mirrors are superior to refractive glass lenses in almost every way No. Reflective designs (mirrors) are usually of the casigrain type, and casigrain designs offer very narrow but limited zoom range field of views. This is at the cost of obscuration of the secondary mirror. Note that there are still refractive elements (lenses) in a casigrain design. This very narrow fov is why such designs are prefered in telescopes and other narrow fov application areas. The majority of lens designs are refractive and this should give you an indication that a statement such as mirrors are superior to refractive designs simply is not true. Edit - added application areas