Optical telescopes: two basic types are reflecting-collect light through mirrors refracting -collect light through lens focus point- where the light meets at one point focus length- where image of the object is formed Telescope size Big telescope=more light captured Angular resolution- a measure of the sharpness and clarity of an image (high resolution=shaper images) capture more details magnification=capture more details with the size of the image . onced used glass plates to collect data but now uses an CDC- which are highly effective electronic light detectors to collect data Earth atmosphere makes it difficult to gather clear images seeing- a measure of smearing of light from celestial objects due to turbulent layers of air in the atmosphere adaptive optics- backside of deformable mirror with attractors that change the mirror shape • A telescope’s most important function is to gather as much light as possible. When possible, it also resolves (reveals details) and magnifies an object. • Reflecting telescopes, or reflectors, produce images by reflecting light rays from concave mirrors to a focal point or focal plane. • Refracting telescopes, or refractors, produce images by bending light rays as they pass through glass lenses. Glass impurity, opacity to certain wavelengths, and structural difficulties make it inadvisable to build extremely large refractors. Reflectors are not subject to the problems that limit the usefulness of refractors. • Earth-based telescopes are being built with active optics and adaptive