Refracting telescopes use a lens to focus light. The Swedish 1-m Solar Telescope, with a lens diameter of 43 inches, is technically the largest, with 39 inches clear for the aperture. The second largest refracting telescope in the world is the Yerkes Observatory 40 inch (102 cm) refractor, used for astronomical and scientific observation for over a century. The next largest refractor telescopes are the James Lick telescope, and the Meudon Great Refractor.
Most are classical great refractors, which used achromatic doublets on an equatorial mount. However, other large refractors include a 21st-century solar telescope which is not directly comparable because it uses a single element non-achromatic lens, and the short-lived Great Paris Exhibition Telescope of 1900. It used a 78-inch (200 cm) Focault siderostat for aiming light into the Image-forming optical system part of the telescope, which had a 125 cm diameter lens. Using a siderostat incurs a reflective loss. Larger meniscus lenses have been used in later catadioptric telescopes which mix refractors and reflectors in the image-forming part of the telescope. As with reflecting telescopes, there was an ongoing struggle to balance cost with size, quality, and usefulness.
List This list includes some additional examples, such as the Great Paris telescope, which also used a mirror, and some solar telescopes which may have more complicated optical configurations. The SST has an optical aperture of 98 cm (39.37"), although the lens itself is 110 cm (43.31"). It is a single element lens whereas most of this list are doublets, with a crown and flint lens elements.
Name/Observatory Location at debut Modern location name or fate Lens diameter Focal length Built Comments Image Great Paris Exhibition Telescope of 1900 Paris 1900 Exposition Dismantled 1900 125 cm (49.21") 57 m (187 ft) 1900 Fixed lens, scrapped. Aimed via a 2 m reflecting siderostat Swedish 1-m Solar Telescope,ORM La Palma,Spain - 110 cm (43") total diameter