Some other telescope manufacturers use Takahashi refractors as collimating instruments for larger telescopes. Most are classical Great refractors, which used achromatic doublets on an equatorial mount. In 2000, Meade added small 60mm and 70mm achromatic refractors to its ETX line. The era slowly came to end as large reflecting telescopes superseded the great refractors. Refractors were the earliest type of optical telescope. The lenses used in the internal optics are triplet refractors. The company also produced refractors and reflectors with silver-covered mirrors. Refractors suffer from residual chromatic and spherical aberration. Pioneering work on astrophotography was done with great refractors. Bowman's Best started in 1994 and was the first Bowman product to have refractors. Lighting manufacturers use borosilicate glass in their refractors. No larger refractors could be built because of gravity's effect on the lens. Many early discoveries of the Solar System were made with singlet refractors. Apochromatic refractors have objectives built with special, extra-low dispersion materials. In "Legends", large gems called Refractors are used as a power source.