 The major breakthrough in the 1700s, was the discovery of two and even three lens telescopes and increased spread of reflecting telescopes and their designs.In this period reflectors used metal mirrors not metal coated class, which was not pioneered until the next century.The main telescope technologies during this period were refractors with non-achromatic objectives (single lens), speculum metal reflectors, refractors with achromatic doublets objective (doublet lens), and apochromatic triplets (after 1760s) objectives.