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All telescopes collect light and focus the magnified image on a single point. We classify telescopes by their intended application and by their optical design. The two main applications are terrestrial (spotting) and astronomical. The two principle optical designs are reflecting and refracting. Reflecting telescopes use curved, front-surface mirrors to collect light rays and focus them on a single point. Refracting telescopes use curved lenses to collect light and magnify the image by bending the rays as they pass through glass of different composition and thickness.